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I was in my garden a few days ago and found the flower shown in the pictures. Can anybody tell me what this flower is?
Location: Germany / northrhine westfalia
Date: February 2017 Season: Winter
[Edit]: My neighbour thinks it is a Anemone hupehensis (en.wikipedia.org/wiki/Anemone_hupehensis), could be right.
I think it is Anemone hupehensis. We have this species in our garden, and the seeds and dead leaves look very similar to the ones in your picture. The leaves are large,jagged and palmate and they have beautiful flowers in the summer/autumn (I've seen red, pink and white). The fruits/seeds also look very distinctive and cotton-like. The species is originally from Asia/China.
Here is a picture of the fruits/seeds:
(Hard to find good ones, this from Instagram page http://www.ipopam.com/tag/höstanemoner)
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Biology, study of living things and their vital processes. The field deals with all the physicochemical aspects of life. The modern tendency toward cross-disciplinary research and the unification of scientific knowledge and investigation from different fields has resulted in significant overlap of the field of biology with other scientific disciplines. Modern principles of other fields—chemistry, medicine, and physics, for example—are integrated with those of biology in areas such as biochemistry, biomedicine, and biophysics.
What is biology?
Biology is a branch of science that deals with living organisms and their vital processes. Biology encompasses diverse fields, including botany, conservation, ecology, evolution, genetics, marine biology, medicine, microbiology, molecular biology, physiology, and zoology.
Why is biology important?
As a field of science, biology helps us understand the living world and the ways its many species (including humans) function, evolve, and interact. Advances in medicine, agriculture, biotechnology, and many other areas of biology have brought improvements in the quality of life. Fields such as genetics and evolution give insight into the past and can help shape the future, and research in ecology and conservation inform how we can protect this planet’s precious biodiversity.
Where do biology graduates work?
Biology graduates can hold a wide range of jobs, some of which may require additional education. A person with a degree in biology could work in agriculture, health care, biotechnology, education, environmental conservation, research, forensic science, policy, science communication, and many other areas.
Biology is subdivided into separate branches for convenience of study, though all the subdivisions are interrelated by basic principles. Thus, while it is custom to separate the study of plants (botany) from that of animals (zoology), and the study of the structure of organisms (morphology) from that of function (physiology), all living things share in common certain biological phenomena—for example, various means of reproduction, cell division, and the transmission of genetic material.
Biology is often approached on the basis of levels that deal with fundamental units of life. At the level of molecular biology, for example, life is regarded as a manifestation of chemical and energy transformations that occur among the many chemical constituents that compose an organism. As a result of the development of increasingly powerful and precise laboratory instruments and techniques, it is possible to understand and define with high precision and accuracy not only the ultimate physiochemical organization (ultrastructure) of the molecules in living matter but also the way living matter reproduces at the molecular level. Especially crucial to those advances was the rise of genomics in the late 20th and early 21st centuries.
Cell biology is the study of cells—the fundamental units of structure and function in living organisms. Cells were first observed in the 17th century, when the compound microscope was invented. Before that time, the individual organism was studied as a whole in a field known as organismic biology that area of research remains an important component of the biological sciences. Population biology deals with groups or populations of organisms that inhabit a given area or region. Included at that level are studies of the roles that specific kinds of plants and animals play in the complex and self-perpetuating interrelationships that exist between the living and the nonliving world, as well as studies of the built-in controls that maintain those relationships naturally. Those broadly based levels—molecules, cells, whole organisms, and populations—may be further subdivided for study, giving rise to specializations such as morphology, taxonomy, biophysics, biochemistry, genetics, epigenetics, and ecology. A field of biology may be especially concerned with the investigation of one kind of living thing—for example, the study of birds in ornithology, the study of fishes in ichthyology, or the study of microorganisms in microbiology.
- Plant Chemistry
- Plant Evolution
- Plants and Humans
- Plant Parts
- Seed Dispersal
As the botanists with UntamedScience add more information this year, we will also add educational videos to these pages. Be patient with us though, these pages are all under construction …
Plant Classifications: Meaning and Types
In this article we will discuss about the Meaning and Types of Plant Classifications.
Meaning of Plant Classification:
Plant Classification is the arrangement of plants into groups and categories for a clear understanding, proper study and effective organization. According to Radford (1986) “classification is the arrangement of groups of plants with particular circumscriptions by rank and position according to artificial criteria, phenetic similarities, or phylogenetic relationships”.
The early civilization of India, Egypt and China who had a fair knowledge of plants used both as food as well as medicinal purposes, also practiced a sort of plants taxonomy.
Vrikshayurveda compiled by parasara before the beginning of the christian era is one of the earliest Indian works, which deals with plants in a scientific manner and follows a classification largely based on comparative morphology of plants, and it was considered to be more advanced than the one developed in Europe before 18th century.
Several families known as ganas are clearly distinguished in Vrikshayurveda, which are easily recognizable even today. As for example, it mentions the flowers of Samiganyam as bypogynous with a gameosepalous calyx, five petals of different sizes and the fruit a legume with the seeds on the side. This evidently indicates to the family Leguminosae.
A plant classification system has predictive value and provides an index to information storage and retrieval on that plant. Since systematics today is very much a reflection of the past, a historical review revealing the historical period and the technologies available during the historical periods needs to be summarized.
Types of Plant Classification:
A. Evolutionary Classifications:
(i) Charles Darwin (1809-1882):
His famous work includes On the Origin of Species by Means of Natural Selection (1859). Darwin was strongly influenced by observations during the voyage of the H.M.S. Beagle to the Galapagos Islands. His observation on the differences in animals (e.g. fishes) and plants on different islands prompted his mechanism for evolutionary change, i.e. natural selection.
Darwin thought then that the earth was much older than 6000 years and that evolutionary change occurs through gradual, accumulated differences. At the same time another scientist, Alfred R. Wallace, was working in the East Indies and developed a very similar theory i.e. theory of evolution.
Both theories were presented at the meetings of the London Linnaean Society in 1858, and this concept of evolutionary change was embraced by most scientists, including Haekel whose Tree of Life (1866) depicted all taxa (Protists, Plants, and Animals).
(ii) George Bentham (1800-1884) and Sir Joseph D. Hooker (1817-1911):
Genera Plantarum was published after Darwin’s Origin of Species, but it was not possible to change the system to reflect new evolutionary concepts despite the fact that both Bentham and Hooker were great champions of this theory. Bentham and Hooker’s system is post- Darwinian in chronology but pre-Darwinian in concept.
They named 200 families and 7,569 genera, with fabulously detailed, often original descriptions. Many herbaria in the world are still arranged according to this system. They recognized monocots and dicots and began the latter with the polypetalous plants.
B. Phylogenetic Classifications:
He is not considered a major figure in systems of plant classification, but he was the first professor of botany at U.S. University. His most famous work includes A Manual of Botany of the Northern United States (1848). Gray’s Manual of Botany was published later by M. L. Fernald.
(ii) Adolph Engler (1844-1930) and K. A. E. Prantl (1849-1893):
The first phylogenetic systems came from Botanical Garden in Berlin. Engler and Prantl believed that the plant classification system should reflect the evolutionary history and their greatest work Die Naturlichen Pflanzenfamilien, adopted a system that proceeded from simple structures to complex.
Unisexual, cone-like flowers (catkins) were considered to be primitive (alder, birch, etc.). This was the first major phylogenetic classification. This system is used today in many herbaria and floras and very useful for a modern taxonomist, but the concepts of what is primitive and advanced has changed today.
(iii) Charles Edwin Bessey (1845-1915):
He was a student of Asa Gray and he developed a set of “dicta” (rules) stating which characters are primitive and which are advanced in flowering plants. Not all are considered correct today but many are. The Magnolia type flower was considered primitive, not the unisexual catkin-bearing plants. His published work is The Phylogenetic Taxonomy of Flowering Plants.
(iv) John Hutchinson (1884-1972):
He worked at Kew Gardens and published The Families of Flowering Plants and Genera of Flowering Plants. He considered woody and herbaceous to be of fundamentally different evolutionary trends. Not much of this plant classification is used today.
(v) Robert F. Thorne (1920 to present):
He works at Rancho Santa Anna Botanical Garden in Claremont, CA. His work includes A Phylogenetic Classification of the Angiosperm.
(vi) Armen Takhtajan (1910 to present):
He was initially at Lenningrad, but now spends most time at New York Botanical Garden. His work Flowering Plants: Origin and Dispersal was an influential early work. A revision of this classification appeared in 1997 as Diversity and Classification of Flowering Plants.
(vii) Rolf Dahlgren (1932-1985):
He worked at the University of Copenhagen. His work includes A Revised System of plant Classification of the Angiosperms.
(viii) Arthur Cronquist (1919-1991):
He worked most of his life at the New York Botanical Garden. Many of his ideas are Besseyan with some influence from Takhtajan. His most famous work includes An Integrated System of plant Classification of Flowering Plants (1981), which has been revised in 1988 and is much adopted today.
ABC Model of Flower Development | Plants
In this article we will discuss about the ABC model of flower development.
The ABC model of flower development in angiosperm demonstrates the presence of three classes of genes that regulate the development of floral organs. The genes are referred to as class A genes, class B genes and class C gene. These genes and the interaction between them induce the development of floral organs.
Many literatures on molecular genetics and Internet Websites provide articles on ABC model. In the following essay the basic concept of ABC model will be discussed in brief. The analysis of ABC model is based on the use of molecular genetics and formulated on the observation that mutants induce right floral organs to develop in wrong whorls.
In the flower of angiosperms there are usually four concentric whorls of organs, i.e. sepal, petal, stamen and carpel that are formed in whorl 1, whorl 2, whorl 3 and whorl 4 respectively, the whorl 1 being on the peripheral side.
In the whorl 1 class A genes when expressed induce the development of sepals. The interaction between class A and class B genes induce the development of petals in the whorl 2. Stamens are formed in the whorl 3 as a result of interaction between class B and class C genes.
In the whorl 4 class C gene induces the formation of carpel. So the summary of ABC model is: class A genes together and class C gene alone are responsible for the development of sepals and carpel respectively. The class B genes and class A genes function cooperatively to determine the development of petals. The class B genes and class C gene act together to induce the development of stamens (Fig. 30.12).
Coen et al. (1991) formulated the ABC model. While analyzing the mutations affecting flower structure Coen et al. identified the class ABC genes that direct flower development. They also formulated the molecular models of how floral meristem and organ identity may be specified. They have shown that the distantly related angiosperm plants use homologous mechanisms in pattern formation of floral organs. Ex. Arabidopsis thaliana and Antirrhinum majus.
The following two have led to formulate ABC model:
(1) The discovery of homeotic mutants (homeotic genes identify specific floral organs and help the organ to develop in respective whorl. The homeotic mutant has inappropriate expression—that is, it induces right organ to develop in wrong whorl. As for example — petals emerge in the whorl where normally stamens develop).
(2) The observation that each of the genes that induce the formation of an organ in a flower has an effect on two groups of floral organs, i.e. sepal and petals or petals and stamens.
Class A, B and C genes are homeotic genes. They determine the identity of different floral organs and induce the organs to develop in their respective whorls.
The homeotic mutants have defects in floral organ development and induce the right organs to develop in wrong whorls/place, i.e. one floral organ develops in the whorl, which is the normal position of another floral organs. Petals, for example, develop in the whorl where stamens are normally to be formed.
In each whorl of a flower there is one or more homeotic genes and their cooperative functions determine the organ to be formed in that whorl. For example, the activity of class A genes is restricted to whorls 1 and 2. The class B genes have function in whorls 2 and 3. The class C gene functions in whorls 3 and 4.
Another way of describing the function of class A, B and C genes is that—in whorl 1, the class A gene-function alone determines the formation of sepals in whorl 2, class A and B gene-functions both determine the formation of petals in whorl 3, class B and C gene-functions both determine the emergence of stamens and in whorl 4, class C gene-function alone determines the carpel formation.
In Arabidopsis there are two genes in class A, two genes in class B and one gene in class C (Table 30.1). The most characteristic feature of these homeotic genes is in the identification of floral organs and in the determinacy of position / whorl of their emergence in a floral meristem. The two genes of class A and the two genes of class B act cooperatively.
The function of class A genes is confined to whorls 1 and 2. Similarly the function of class C gene is restricted in whorls 3 and 4. This can be interpreted in another way. In the whorls 1 and 2 the function of class A genes prevents class C gene from functioning in the same whorls. Similarly the function of class C gene prevents class A genes from functioning in the whorls 3 and 4.
Any mutation in class A genes with defects in floral organ development will invite class C gene to express in whorls 1 and 2. The class C gene, in class A mutants, will express in whorls 1 and 2 in addition to the normal whorls 3 and 4.
Similarly any mutation in class C gene with defects in floral organ development will lead to the encroachment of the function of class A genes. The class A genes will express in the whorls 3 and 4 in addition to the normal whorls 1 and 2.
The following three examples of homeotic mutant genes will illustrate the above discussion (Fig. 30.13):
(1) The flower of Arabidopsis with class A mutants, such as apetala 1(ap 1) shows the following pattern of floral organs (Fig. 3.13.II): whorl 1 shows bract-like structure with carpelloid characteristics whorl 2 shows stamens whorl 3 shows stamens and whorl 4 shows carpel.
The pattern of floral organ formation in whorls 1 and 2 is changed. In ap 1 mutants the activity of two genes of class A is lost. So the class C gene expressed in whorls 1 and 2 in addition to whorls 3 and 4. As a result carpelloid organ developed in whorl 1 and stamens formed in whorl 2. In the whorls 3 and 4 stamens and carpel respectively are formed similar to wild type (Fig. 30.13.I).
(2) Example: Flower of Arabidopsis with class B mutant, such as apetala 3 (ap 3): The flower shows sepals only both in whorls 1 and 2, while the whorls 3 and 4 show carpel only (Fig. 30.13III). Class B mutant contains loss-of-function genes and as a result class A genes express in whorls 1 and 2 and class C gene alone expresses in whorls 3 and 4. In ap 3 mutants in whorl 2, sepals are formed instead of petals and in whorl 3, carpel is formed instead of stamens.
(3) In Arabidopsis the class C gene contains the sole gene agamous (ag). Arabidopsis flower with agamous (ag) mutant consists of many sepals and petals. The reproductive organs – stamens and carpel are not formed in the whorls 3 and 4. Class C gene with ag mutant contains loss-of-function gene. As a result class A genes express in whorls 3 and 4 in addition to 1 and 2. In ag mutant sepals and petals are formed in whorls 3 and 4 instead of stamens and carpel. The literature of Howell provides the scan electron micrograph of flower phenotypes of the floral homeotic mutants of class A, B and C genes.
In Arabidopsis it was observed that in all the mutants one homeotic gene remains functional in each whorl. The flower with class ABC triple mutant shows sepals in each whorl. In ABC triple mutant, the genes required for floral organ formation become nonfunctional. As a result sepals or leaves are formed in each whorl, as homeotic mutants specify no floral organs. This observation led Botanists to regard ‘flowers as modified leaves’ on the basis of molecular genetics.
The important feature of ABC model is that it can predict the type of floral organ to be induced to develop in any whorl. Krizek et al. (1996) was successful to induce any one of the four different floral parts in whorl 1 of Arabidopsis flower. This became possible by genetic manipulations of right combination of homeotic selector genes.
The ABC model appears to be simple, but a completely different picture is obtained when it is analyzed on the basis of molecular genetics and in molecular terms.
The analysis includes the structure of different classes of homeotic genes, the homeotic mutants, the co-operative function between homeotic genes, mutual exclusion in the expression of class A and C genes in the same whorl, the identification of floral homeotic genes and their isolation by cloning, the production of MADS box protein by homeotic mutants, the study of genes that mediate the interaction between floral meristem and floral organ development, presence or absence of different classes of transcription factors etc., the details of which can be obtained in the literatures on molecular genetics.
Arabidopsis thaliana belongs to the family Brassicaceae and has become the model organism for understanding the genetics and molecular biology of flowering plants like mice and Drosophila in animal researches due to following reasons:
(i) It has five chromosomes (n = 5) and so this small-size-genome is advantageous in gene mapping and sequencing.
(ii) The size of plant is small and so can be cultivated in a small space and requires modest indoor facilities.
(iii) It has rapid life cycle and takes about six weeks from germination to mature seeds.
(iv) An individual plant produces several thousand seeds.
(v) ‘The Arabidopsis genome is among the smallest in higher plants, with a haploid size of about 100 megabases (mb) of DNA. With a small genome size it was expected that there would be fewer problems with gene duplication’— Howell.
(vi) It is easily transformable with T-DNA mediated transformation.
In 2004 ABCE model has been formulated. The characterization of sepallata 1, 2, 3 triple mutants in Arabidopsis has led to the above formulation. It is regarded that the class E genes have important role in the development of floral organs.
How Plants Grow
Figure 1. There must be an area of growth, similar to how the bones in your fingers, arms, and legs grow longer. There is, and it is called the apical meristem, which is shown here.
Most plants continue to grow throughout their lives. Like other multicellular organisms, plants grow through a combination of cell growth and cell division. Cell growth increases cell size, while cell division (mitosis) increases the number of cells. As plant cells grow, they also become specialized into different cell types through cellular differentiation. Once cells differentiate, they can no longer divide. How do plants grow or replace damaged cells after that?
The key to continued growth and repair of plant cells is meristem. Meristem is a type of plant tissue consisting of undifferentiated cells that can continue to divide and differentiate.
Apical meristems are found at the apex, or tip, of roots and buds, allowing roots and stems to grow in length and leaves and flowers to differentiate. Roots and stems grow in length because the meristem adds tissue “behind” it, constantly propelling itself further into the ground (for roots) or air (for stems). Often, the apical meristem of a single branch will become dominant, suppressing the growth of meristems on other branches and leading to the development of a single trunk. In grasses, meristems at the base of the leaf blades allow for regrowth after grazing by herbivores—or mowing by lawnmowers.
Apical meristems differentiate into the three basic types of meristem tissue which correspond to the three types of tissue: protoderm produces new epidermis, ground meristem produces ground tissue, and procambium produces new xylem and phloem. These three types of meristem are considered primary meristem because they allow growth in length or height, which is known as primary growth.
Figure 2. Microphotograph of the root tip of a broad bean show rapidly dividing apical meristem tissue just behind the root cap. Numerous cells in various stages of mitosis can be observed.
Secondary meristems allow growth in diameter (secondary growth) in woody plants. Herbaceous plants do not have secondary growth. The two types of secondary meristem are both named cambium, meaning “exchange” or “change.” Vascular cambiumproduces secondary xylem (toward the center of the stem or root) and phloem (toward the outside of the stem or root), adding growth to the diameter of the plant. This process produces wood, and builds the sturdy trunks of trees. Cork cambiumlies between the epidermis and the phloem, and replaces the epidermis of roots and stems with bark, one layer of which is cork.
Figure 3. Primary and secondary growth
Woody plants grow in two ways. Primary growth adds length or height, mediated by apical meristem tissue at the tips of roots and shoots—which is difficult to show clearly in cross-sectional diagrams. Secondary growth adds to the diameter of a stem or root vascular cambium adds xylem (inward) and phloem (outward), and cork cambium replaces epidermis with bark.
Watch this time-lapse video of plant growth. Note that there isn’t any narration in the video.
In Summary: How Plants Grow
Most plants continue to grow as long as they live. They grow through a combination of cell growth and cell division (mitosis). The key to plant growth is meristem, a type of plant tissue consisting of undifferentiated cells that can continue to divide and differentiate. Meristem allows plant stems and roots to grow longer (primary growth) and wider (secondary growth).
The basic principles of modern biology
Four principles unify modern biology, according to the book "Managing Science" (Springer New York, 2010):
- Cell theory is the principle that all living things are made of fundamental units called cells, and all cells come from preexisting cells.
- Gene theory is the principle that all living things have DNA, molecules that code the structures and functions of cells and get passed to offspring. is the principle that all living things maintain a state of balance that enables organisms to survive in their environment. is the principle that describes how all living things can change to have traits that enable them to survive better in their environments. These traits result from random mutations in the organism's genes that are "selected" via a process called natural selection. During natural selection, organisms that have traits better-suited for their environment have higher rates of survival, and then pass those traits to their offspring.
Related Biology Terms
- Codominance – A situation where two alleles are neither dominant nor recessive towards each other and both are expressed as phenotype.
- Diploid – A cell containing two sets of chromosomes, one set from each parent. Diploid cells contain two copies of nearly every gene.
- Gametes – Mature, haploid germ cells from the male and female that can fuse with one another to form a zygote.
- Haploid – A cell containing a single set of chromosomes.
1. Which of these is inherited completely from the mother?
A. Genes for eye color
B. Genes for cystic fibrosis
C. Genes from the Y-chromosome
D. Mitochondrial genes
2. Which of these are assumptions in creating a Punnett square?
A. The alleles for each trait segregate during meiosis
B. Each trait assorts independently of the others
C. Only one gene locus is involved in a particular trait
D. All of the above
3. How many rows and columns would be needed to create a Punnett square for a trihybrid cross?
Perennial plants are most commonly herbaceous (plants that have leaves and stems that die to the ground at the end of the growing season and which show only primary growth) or woody (plants with persistent above grounds stems that survive from one growing season to the next, with primary and secondary growth, or growth in width protected by an outer cortex),  and some are evergreen with persistent foliage without woody stems. They can be short-lived (only a few years) or long-lived. They include a wide assortment of plant groups from non-flowering plants like ferns and liverworts to the highly diverse flowering plants like orchids, grasses, and woody plants. Plants that flower and fruit only once and then die are termed monocarpic or semelparous, these species may live for many years before they flower,  for example, century plant can live for 80 years and grow 30 meters tall before flowering and dying.  However, most perennials are polycarpic (or iteroparous), flowering over many seasons in their lifetime.  Perennials invest more resources than annuals into roots, crowns, and other structures that allow them to live from one year to the next, but have a competitive advantage because that they can commence their growth and fill out earlier in the growing season than annuals, in doing so they can better compete for space and collect more light. 
Perennials typically grow structures that allow them to adapt to living from one year to the next through a form of vegetative reproduction rather than seeding. These structures include bulbs, tubers, woody crowns, rhizomes and turions. They might have specialized stems or crowns that allow them to survive periods of dormancy over cold or dry seasons during the year. Annuals, by contrast, produce seeds to continue the species as a new generation. At the same time, the growing season is suitable, and the seeds survive over the cold or dry period to begin growth when the conditions are again suitable.
Many perennials have specialized features that allow them to survive extreme environmental conditions. Some have adapted to hot or dry conditions and others too cold temperatures they tend to invest resources into their adaptations and often do not flower and set seed until after a few years of growth. In climates that are warm all year long, perennials may grow continuously.  In seasonal climates, their growth is limited by temperature or moisture to a growing season.
Some perennials retain their foliage year-round these are evergreen perennials. Deciduous perennials shed all their leaves part of the year,  they include herbaceous and woody plants herbaceous plants have stems that lack hard, fibrous growth, while woody plants hard stems with buds that survive above ground during dormancy,  some perennials are semi-deciduous, meaning they lose some of their leaves in either winter or summer.  Deciduous perennials shed their leaves when growing conditions are no longer suitable for photosynthesis, such as when it is too cold or dry. In many parts of the world, seasonality is expressed as wet and dry periods rather than warm and cold periods, and deciduous perennials lose their leaves in the dry season. 
Some perennial plants are protected from wildfires because they have underground roots that produce adventitious shoots, bulbs, crowns, or stems  other perennials like trees and shrubs may have thick cork layers that protect the stems. Herbaceous perennials from temperate and alpine regions of the world can tolerate the cold during winters.
Perennial plants may remain dormant for long periods and then recommence growth and reproduction when the environment is more suitable, while most annual plants complete their life cycle during one growing period, and biennials have two growing periods.
The meristem of perennial plants communicates with the hormones produced due to environmental situations (i.e., seasons), reproduction, and stage of development to begin and halt the ability to grow or flower. There is also a distinction between the ability to grow and the actual task of growth. For example, most trees regain the ability to grow during winter but do not initiate physical growth until the spring and summer months. The start of dormancy can be seen in perennials plants through withering flowers, loss of leaves on trees, and halting of reproduction in both flowering and budding plants. 
Perennials species may produce relatively large seeds that have the advantage of generating larger seedlings that can better compete with other plants. Perennials also produce seeds over many years.
Perennials that are cultivated include: woody plants like fruit trees grown for their edible fruits shrubs and trees grown as landscaping ornamentals herbaceous food crops like asparagus, rhubarb, strawberries and subtropical plants not hardy in colder areas such as tomatoes, eggplant, and coleus (which are treated as annuals in colder areas).  Perennials also include plants grown for their flowering and other ornamental value including: bulbs (like tulips, narcissus, and gladiolus) and lawn grass, and other groundcovers, (such as periwinkle [a] and Dichondra). 
Each type of plant must be separated differently for example, plants with fibrous root systems like daylilies, Siberian iris or grasses can be pried apart with two garden forks inserted back to back, or cut by knives. However, plants such as bearded irises have a root system of rhizomes these root systems should be planted with the top of the rhizome just above ground level, with leaves from the following year showing. The point of dividing perennials is to increase the amount of a single breed of plant in your garden.  In the United States more than 900 million dollars worth of potted herbaceous perennial plants were sold in 2019. 
What kind of flower is this? - Biology
The lifecycle of angiosperms follows the alternation of generations explained previously. The haploid gametophyte alternates with the diploid sporophyte during the sexual reproduction process of angiosperms. Flowers contain the plant’s reproductive structures.
A typical flower has four main parts—or whorls—known as the calyx, corolla, androecium, and gynoecium (Figure 1). The outermost whorl of the flower has green, leafy structures known as sepals. The sepals, collectively called the calyx, help to protect the unopened bud. The second whorl is comprised of petals—usually, brightly colored—collectively called the corolla. The number of sepals and petals varies depending on whether the plant is a monocot or dicot. In monocots, petals usually number three or multiples of three in dicots, the number of petals is four or five, or multiples of four and five. Together, the calyx and corolla are known as the perianth . The third whorl contains the male reproductive structures and is known as the androecium. The androecium has stamens with anthers that contain the microsporangia. The innermost group of structures in the flower is the gynoecium , or the female reproductive component(s). The carpel is the individual unit of the gynoecium and has a stigma, style, and ovary. A flower may have one or multiple carpels.
Figure 1. The four main parts of the flower are the calyx, corolla, androecium, and gynoecium. The androecium is the sum of all the male reproductive organs, and the gynoecium is the sum of the female reproductive organs. (credit: modification of work by Mariana Ruiz Villareal)
If all four whorls (the calyx, corolla, androecium, and gynoecium) are present, the flower is described as complete. If any of the four parts is missing, the flower is known as incomplete. Flowers that contain both an androecium and a gynoecium are called perfect, androgynous or hermaphrodites. There are two types of incomplete flowers: staminate flowers contain only an androecium, and carpellate flowers have only a gynoecium (Figure 2).
Figure 2. The corn plant has both staminate (male) and carpellate (female) flowers. Staminate flowers, which are clustered in the tassel at the tip of the stem, produce pollen grains. Carpellate flower are clustered in the immature ears. Each strand of silk is a stigma. The corn kernels are seeds that develop on the ear after fertilization. Also shown is the lower stem and root.
If the anther is missing, what type of reproductive structure will the flower be unable to produce?
Pollen germination has three stages hydration, activation and pollen tube emergence. The pollen grain is severely dehydrated so that its mass is reduced enabling it to be more easily transported from flower to flower. Germination only takes place after rehydration, ensuring that premature germination does not take place in the anther. Hydration allows the plasma membrane of the pollen grain to reform into its normal bilayer organization providing an effective osmotic membrane. Activation involves the development of actin filaments throughout the cytoplasm of the cell, which eventually become concentrated at the point from which the pollen tube will emerge. Hydration and activation continue as the pollen tube begins to grow.  In conifers, the reproductive structures are borne on cones. The cones are either pollen cones (male) or ovulate cones (female), but some species are monoecious and others dioecious. A pollen cone contains hundreds of microsporangia carried on (or borne on) reproductive structures called sporophylls. Spore mother cells in the microsporangia divide by meiosis to form haploid microspores that develop further by two mitotic divisions into immature male gametophytes (pollen grains). The four resulting cells consist of a large tube cell that forms the pollen tube, a generative cell that will produce two sperm by mitosis, and two prothallial cells that degenerate. These cells comprise a very reduced microgametophyte, that is contained within the resistant
The pollen grains are dispersed by the wind to the female, ovulate cone that is made up of many overlapping scales (sporophylls, and thus megasporophylls), each protecting two ovules, each of which consists of a megasporangium (the nucellus) wrapped in two layers of tissue, the integument and the cupule, that were derived from highly modified branches of ancestral gymnosperms. When a pollen grain lands close enough to the tip of an ovule, it is drawn in through the micropyle ( a pore in the integuments covering the tip of the ovule) often by means of a drop of liquid known as a pollination drop. The pollen enters a pollen chamber close to the nucellus, and there it may wait for a year before it germinates and forms a pollen tube that grows through the wall of the megasporangium (=nucellus) where fertilisation takes place. During this time, the megaspore mother cell divides by meiosis to form four haploid cells, three of which degenerate. The surviving one develops as a megaspore and divides repeatedly to form an immature female gametophyte (egg sac). Two or three archegonia containing an egg then develop inside the gametophyte. Meanwhile, in the spring of the second year two sperm cells are produced by mitosis of the body cell of the male gametophyte. The pollen tube elongates and pierces and grows through the megasporangium wall and delivers the sperm cells to the female gametophyte inside. Fertilisation takes place when the nucleus of one of the sperm cells enters the egg cell in the megagametophyte's archegonium. 
In flowering plants, the anthers of the flower produce microspores by meiosis. These undergo mitosis to form male gametophytes, each of which contains two haploid cells. Meanwhile, the ovules produce megaspores by meiosis, further division of these form the female gametophytes, which are very strongly reduced, each consisting only of a few cells, one of which is the egg. When a pollen grain adheres to the stigma of a carpel it germinates, developing a pollen tube that grows through the tissues of the style, entering the ovule through the micropyle. When the tube reaches the egg sac, two sperm cells pass through it into the female gametophyte and fertilisation takes place. 
Pollination may be biotic or abiotic. Biotic pollination relies on living pollinators to move the pollen from one flower to another. Abiotic pollination relies on wind, water or even rain. About 80% of angiosperms rely on biotic pollination. 
Abiotic pollination uses nonliving methods such as wind and water to move pollen from one flower to another. This allows the plant to spend energy directly on pollen rather than on attracting pollinators with flowers and nectar.
By wind Edit
Some 98% of abiotic pollination is anemophily, pollination by wind. This probably arose from insect pollination, most likely due to changes in the environment or the availability of pollinators.    The transfer of pollen is more efficient than previously thought wind pollinated plants have developed to have specific heights, in addition to specific floral, stamen and stigma positions that promote effective pollen dispersal and transfer. 
By water Edit
Pollination by water, hydrophily, uses water to transport pollen, sometimes as whole anthers these can travel across the surface of the water to carry dry pollen from one flower to another.  In Vallisneria spiralis, an unopened male flower floats to the surface of the water, and, upon reaching the surface, opens up and the fertile anthers project forward. The female flower, also floating, has its stigma protected from the water, while its sepals are slightly depressed into the water, allowing the male flowers to tumble in. 
By rain Edit
Rain pollination is used by a small percentage of plants. Heavy rain discourages insect pollination and damages unprotected flowers, but can itself disperse pollen of suitably adapted plants, such as Ranunculus flammula, Narthecium ossifragum, and Caltha palustris.  In these plants, excess rain drains allowing the floating pollen to come in contact with the stigma.  In some orchids ombrophily occurs, and rain water splashes cause the anther cap to be removed, allowing for the pollen to be exposed. After exposure, raindrops causes the pollen to be shot upward, when the stipe pulls them back, and then fall into the cavity of the stigma. Thus, for the orchid Acampe rigida, this allows the plant to self-pollinate, which is useful when biotic pollinators in the environment have decreased. 
Switching methods Edit
It is possible for a plant have varying pollination methods, including both biotic and abiotic pollination. The orchid Oeceoclades maculata uses both rain and butterflies, depending on its environmental conditions. 
More commonly, pollination involves pollinators (also called pollen vectors): organisms that carry or move the pollen grains from the anther of one flower to the receptive part of the carpel or pistil (stigma) of another.  Between 100,000 and 200,000 species of animal act as pollinators of the world's 250,000 species of flowering plant.  The majority of these pollinators are insects, but about 1,500 species of birds and mammals visit flowers and may transfer pollen between them. Besides birds and bats which are the most frequent visitors, these include monkeys, lemurs, squirrels, rodents and possums. 
Entomophily, pollination by insects, often occurs on plants that have developed colored petals and a strong scent to attract insects such as, bees, wasps and occasionally ants (Hymenoptera), beetles (Coleoptera), moths and butterflies (Lepidoptera), and flies (Diptera). The existence of insect pollination dates back to the dinosaur era. 
In zoophily, pollination is performed by vertebrates such as birds and bats, particularly, hummingbirds, sunbirds, spiderhunters, honeyeaters, and fruit bats. Ornithophily or bird pollination is the pollination of flowering plants by birds. Chiropterophily or bat pollination is the pollination of flowering plants by bats. Plants adapted to use bats or moths as pollinators typically have white petals, strong scent and flower at night, whereas plants that use birds as pollinators tend to produce copious nectar and have red petals. 
Insect pollinators such as honey bees (Apis spp.),  bumblebees (Bombus spp.),   and butterflies (e.g., Thymelicus flavus)  have been observed to engage in flower constancy, which means they are more likely to transfer pollen to other conspecific plants.  This can be beneficial for the pollinators, as flower constancy prevents the loss of pollen during interspecific flights and pollinators from clogging stigmas with pollen of other flower species. It also improves the probability that the pollinator will find productive flowers easily accessible and recognisable by familiar clues. 
Some flowers have specialized mechanisms to trap pollinators to increase effectiveness.  Other flowers will attract pollinators by odor. For example, bee species such as Euglossa cordata are attracted to orchids this way, and it has been suggested that the bees will become intoxicated during these visits to the orchid flowers, which last up to 90 minutes.  However, in general, plants that rely on pollen vectors tend to be adapted to their particular type of vector, for example day-pollinated species tend to be brightly coloured, but if they are pollinated largely by birds or specialist mammals, they tend to be larger and have larger nectar rewards than species that are strictly insect-pollinated. They also tend to spread their rewards over longer periods, having long flowering seasons their specialist pollinators would be likely to starve if the pollination season were too short. 
As for the types of pollinators, reptile pollinators are known, but they form a minority in most ecological situations. They are most frequent and most ecologically significant in island systems, where insect and sometimes also bird populations may be unstable and less species-rich. Adaptation to a lack of animal food and of predation pressure, might therefore favour reptiles becoming more herbivorous and more inclined to feed on pollen and nectar.  Most species of lizards in the families that seem to be significant in pollination seem to carry pollen only incidentally, especially the larger species such as Varanidae and Iguanidae, but especially several species of the Gekkonidae are active pollinators, and so is at least one species of the Lacertidae, Podarcis lilfordi, which pollinates various species, but in particular is the major pollinator of Euphorbia dendroides on various Mediterranean islands. 
Mammals are not generally thought of as pollinators, but some rodents, bats and marsupials are significant pollinators and some even specialise in such activities. In South Africa certain species of Protea (in particular Protea humiflora, P. amplexicaulis, P. subulifolia, P. decurrens and P. cordata) are adapted to pollination by rodents (particularly Cape Spiny Mouse, Acomys subspinosus)  and elephant shrews (Elephantulus species).  The flowers are borne near the ground, are yeasty smelling, not colourful, and sunbirds reject the nectar with its high xylose content. The mice apparently can digest the xylose and they eat large quantities of the pollen.  In Australia pollination by flying, gliding and earthbound mammals has been demonstrated.  Examples of pollen vectors include many species of wasps, that transport pollen of many plant species, being potential or even efficient pollinators. 
Pollination can be accomplished by cross-pollination or by self-pollination:
- Cross-pollination, also called allogamy, occurs when pollen is delivered from the stamen of one flower to the stigma of a flower on another plant of the same species.  Plants adapted for cross-pollination have several mechanisms to prevent self-pollination the reproductive organs may be arranged in such a way that self-fertilisation is unlikely, or the stamens and carpels may mature at different times. 
- Self-pollination occurs when pollen from one flower pollinates the same flower or other flowers of the same individual.  It is thought to have evolved under conditions when pollinators were not reliable vectors for pollen transport, and is most often seen in short-lived annual species and plants that colonize new locations.  Self-pollination may include autogamy, where pollen is transferred to the female part of the same flower or geitonogamy, when pollen is transferred to another flower on the same plant.  Plants adapted to self-fertilize often have similar stamen and carpel lengths. Plants that can pollinate themselves and produce viable offspring are called self-fertile. Plants that cannot fertilize themselves are called self-sterile, a condition which mandates cross-pollination for the production of offspring. 
- Cleistogamy: is self-pollination that occurs before the flower opens. The pollen is released from the anther within the flower or the pollen on the anther grows a tube down the style to the ovules. It is a type of sexual breeding, in contrast to asexual systems such as apomixis. Some cleistogamous flowers never open, in contrast to chasmogamous flowers that open and are then pollinated. Cleistogamous flowers are by necessity found on self-compatible or self-fertile plants.  Although certain orchids and grasses are entirely cleistogamous, other plants resort to this strategy under adverse conditions. Often there may be a mixture of both cleistogamous and chasmogamous flowers, sometimes on different parts of the plant and sometimes in mixed inflorescences. The ground bean produces cleistogamous flowers below ground, and mixed cleistogamous and chasmogamous flowers above. 
Geranium incanum, like most geraniums and pelargoniums, sheds its anthers, sometimes its stamens as well, as a barrier to self-pollination. This young flower is about to open its anthers, but has not yet fully developed its pistil.
These Geranium incanum flowers have opened their anthers, but not yet their stigmas. Note the change of colour that signals to pollinators that it is ready for visits.
This Geranium incanum flower has shed its stamens, and deployed the tips of its pistil without accepting pollen from its own anthers. (It might of course still receive pollen from younger flowers on the same plant.)
An estimated 48.7% of plant species are either dioecious or self-incompatible obligate out-crossers.  It is also estimated that about 42% of flowering plants have a mixed mating system in nature.  In the most common kind of mixed mating system, individual plants produce a single type of flower and fruits may contain self-pollinated, out-crossed or a mixture of progeny types.
Pollination also requires consideration of pollenizers, the plants that serve as the pollen source for other plants. Some plants are self-compatible (self-fertile) and can pollinate and fertilize themselves. Other plants have chemical or physical barriers to self-pollination.
In agriculture and horticulture pollination management, a good pollenizer is a plant that provides compatible, viable and plentiful pollen and blooms at the same time as the plant that is to be pollinated or has pollen that can be stored and used when needed to pollinate the desired flowers. Hybridization is effective pollination between flowers of different species, or between different breeding lines or populations. see also Heterosis.
Peaches are considered self-fertile because a commercial crop can be produced without cross-pollination, though cross-pollination usually gives a better crop. Apples are considered self-incompatible, because a commercial crop must be cross-pollinated. Many commercial fruit tree varieties are grafted clones, genetically identical. An orchard block of apples of one variety is genetically a single plant. Many growers now consider this a mistake. One means of correcting this mistake is to graft a limb of an appropriate pollenizer (generally a variety of crabapple) every six trees or so. [ citation needed ]
The first fossil record for abiotic pollination is from fern-like plants in the late Carboniferous period. Gymnosperms show evidence for biotic pollination as early as the Triassic period. Many fossilized pollen grains show characteristics similar to the biotically dispersed pollen today. Furthermore, the gut contents, wing structures, and mouthpart morphology of fossilized beetles and flies suggest that they acted as early pollinators. The association between beetles and angiosperms during the early Cretaceous period led to parallel radiations of angiosperms and insects into the late Cretaceous. The evolution of nectaries in late Cretaceous flowers signals the beginning of the mutualism between hymenopterans and angiosperms.
Bees provide a good example of the mutualism that exists between hymenopterans and angiosperms. Flowers provide bees with nectar (an energy source) and pollen (a source of protein). When bees go from flower to flower collecting pollen they are also depositing pollen grains onto the flowers, thus pollinating them. While pollen and nectar, in most cases, are the most notable reward attained from flowers, bees also visit flowers for other resources such as oil, fragrance, resin and even waxes.  It has been estimated that bees originated with the origin or diversification of angiosperms.  In addition, cases of coevolution between bee species and flowering plants have been illustrated by specialized adaptations. For example, long legs are selected for in Rediviva neliana, a bee that collects oil from Diascia capsularis, which have long spur lengths that are selected for in order to deposit pollen on the oil-collecting bee, which in turn selects for even longer legs in R. neliana and again longer spur length in D. capsularis is selected for, thus, continually driving each other's evolution. 
The most essential staple food crops on the planet, like wheat, maize, rice, soybeans and sorghum   are wind pollinated or self pollinating. When considering the top 15 crops contributing to the human diet globally in 2013, slightly over 10% of the total human diet of plant crops (211 out of 1916 kcal/person/day) is dependent upon insect pollination. 
Pollination management is a branch of agriculture that seeks to protect and enhance present pollinators and often involves the culture and addition of pollinators in monoculture situations, such as commercial fruit orchards. The largest managed pollination event in the world is in Californian almond orchards, where nearly half (about one million hives) of the US honey bees are trucked to the almond orchards each spring. New York's apple crop requires about 30,000 hives Maine's blueberry crop uses about 50,000 hives each year. The US solution to the pollinator shortage, so far, has been for commercial beekeepers to become pollination contractors and to migrate. Just as the combine harvesters follow the wheat harvest from Texas to Manitoba, beekeepers follow the bloom from south to north, to provide pollination for many different crops. [ citation needed ]
In America, bees are brought to commercial plantings of cucumbers, squash, melons, strawberries, and many other crops. Honey bees are not the only managed pollinators: a few other species of bees are also raised as pollinators. The alfalfa leafcutter bee is an important pollinator for alfalfa seed in western United States and Canada. Bumblebees are increasingly raised and used extensively for greenhouse tomatoes and other crops.
The ecological and financial importance of natural pollination by insects to agricultural crops, improving their quality and quantity, becomes more and more appreciated and has given rise to new financial opportunities. The vicinity of a forest or wild grasslands with native pollinators near agricultural crops, such as apples, almonds or coffee can improve their yield by about 20%. The benefits of native pollinators may result in forest owners demanding payment for their contribution in the improved crop results – a simple example of the economic value of ecological services. Farmers can also raise native crops in order to promote native bee pollinator species as shown with L. vierecki in Delaware  and L. leucozonium in southwest Virginia. 
The American Institute of Biological Sciences reports that native insect pollination saves the United States agricultural economy nearly an estimated $3.1 billion annually through natural crop production  pollination produces some $40 billion worth of products annually in the United States alone. 
Pollination of food crops has become an environmental issue, due to two trends. The trend to monoculture means that greater concentrations of pollinators are needed at bloom time than ever before, yet the area is forage poor or even deadly to bees for the rest of the season. The other trend is the decline of pollinator populations, due to pesticide misuse and overuse, new diseases and parasites of bees, clearcut logging, decline of beekeeping, suburban development, removal of hedges and other habitat from farms, and public concern about bees. Widespread aerial spraying for mosquitoes due to West Nile fears is causing an acceleration of the loss of pollinators.
In some situations, farmers or horticulturists may aim to restrict natural pollination to only permit breeding with the preferred individuals plants. This may be achieved through the use of pollination bags.
Improving pollination in areas with suboptimal bee densities Edit
In some instances growers’ demand for beehives far exceeds the available supply. The number of managed beehives in the US has steadily declined from close to 6 million after WWII, to less than 2.5 million today. In contrast, the area dedicated to growing bee-pollinated crops has grown over 300% in the same time period. Additionally, in the past five years there has been a decline in winter managed beehives, which has reached an unprecedented rate of colony losses at near 30%.     At present, there is an enormous demand for beehive rentals that cannot always be met. There is a clear need across the agricultural industry for a management tool to draw pollinators into cultivations and encourage them to preferentially visit and pollinate the flowering crop. By attracting pollinators like honey bees and increasing their foraging behavior, particularly in the center of large plots, we can increase grower returns and optimize yield from their plantings. ISCA Technologies,  from Riverside California, created a semiochemical formulation called SPLAT Bloom, that modifies the behavior of honey bees, inciting them to visit flowers in every portion of the field.
Loss of pollinators, also known as Pollinator decline (of which colony collapse disorder is perhaps the most well known) has been noticed in recent years. These loss of pollinators have caused a disturbance in early plant regeneration processes such as seed dispersal and pollination. Early processes of plant regeneration greatly depend on plant-animal interactions and because these interactions are interrupted, biodiversity and ecosystem functioning are threatened.  Pollination by animals aids in the genetic variability and diversity within plants because it allows for out-crossing instead for self-crossing. Without this genetic diversity there would be a lack of traits for natural selection to act on for the survival of the plant species. Seed dispersal is also important for plant fitness because it allows plants the ability to expand their populations. More than that, it permits plants to escape environments that have changed and have become difficult to reside in. All of these factors show the importance of pollinators for plants, which are a significant part of the foundation for a stable ecosystem. If only a few species of plants depended on Loss of pollinators is especially devastating because there are so many plant species rely on them. More than 87.5% of angiosperms, over 75% of tropical tree species, and 30-40% of tree species in temperate regions depend on pollination and seed dispersal. 
Factors that contribute to pollinator decline include habitat destruction, pesticide, parasitism/diseases, and climate change.  The more destructive forms of human disturbances are land use changes such as fragmentation, selective logging, and the conversion to secondary forest habitat.  Defaunation of frugivores is also an important driver.  These alterations are especially harmful due to the sensitivity of the pollination process of plants.  Research on tropical palms found that defaunation has caused a decline in seed dispersal, which causes a decrease in genetic variability in this species.  Habitat destruction such as fragmentation and selective logging remove areas that are most optimal for the different types of pollinators, which removes pollinators food resources, nesting sites, and leads to isolation of populations.  The effect of pesticides on pollinators has been debated because it is difficult to determine that a single pesticide is the cause as opposed to a mixture or other threats.  Whether exposure alone causes damage, or if the duration and potency are also factors is unknown.  However, insecticides have negative effects, as in the case of neonicotinoids that harm bee colonies. Many researchers believe it is the synergistic effects of these factors which are ultimately detrimental to pollinator populations. 
In the agriculture industry, climate change is causing a "pollinator crisis". This crisis is affecting the production of crops, and the relating costs, due to a decrease in pollination processes.  This disturbance can be phenological or spatial. In the first case, species that normally occur in similar seasons or time cycles, now have different responses to environmental changes and therefore no longer interact. For example, a tree may flower sooner than usual, while the pollinator may reproduce later in the year and therefore the two species no longer coincide in time. Spatial disturbances occur when two species that would normally share the same distribution now respond differently to climate change and are shifting to different regions.  
Examples of affected pollinators Edit
The most known and understood pollinator, bees, have been used as the prime example of the decline in pollinators. Bees are essential in the pollination of agricultural crops and wild plants and are one of the main insects that perform this task.  Out of the bees species, the honey bee or Apis mellifera has been studied the most and in the United States, there has been a loss of 59% of colonies from 1947 to 2005.  The decrease in populations of the honey bee have been attributed to pesticides, genetically modified crops, fragmentation, parasites and diseases that have been introduced.  There has been a focus on neonicotinoids effects on honey bee populations. Neonicotinoids insecticides have been used due to its low mammalian toxicity, target specificity, low application rates, and broad spectrum activity. However, the insecticides are able to make its way throughout the plant, which includes the pollen and nectar. Due to this, it has been shown to effect on the nervous system and colony relations in the honey bee populations. 
Butterflies too have suffered due to these modifications. Butterflies are helpful ecological indicators since they are sensitive to changes within the environment like the season, altitude, and above all, human impact on the environment. Butterfly populations were higher within the natural forest and were lower in open land. The reason for the difference in density is the fact that in open land the butterflies would be exposed to desiccation and predation. These open regions are caused by habitat destruction like logging for timber, livestock grazing, and firewood collection. Due to this destruction, butterfly species' diversity can decrease and it is known that there is a correlation in butterfly diversity and plant diversity. 
Food security and pollinator decline Edit
Besides the imbalance of the ecosystem caused by the decline in pollinators, it may jeopardise food security. Pollination is necessary for plants to continue their populations and 3/4 of the plant species that contribute to the world's food supply are plants that require pollinators.  Insect pollinators, like bees, are large contributors to crop production, over 200 billion dollars worth of crop species are pollinated by these insects.  Pollinators are also essential because they improve crop quality and increase genetic diversity, which is necessary in producing fruit with nutritional value and various flavors.  Crops that do not depend on animals for pollination but on the wind or self-pollination, like corn and potatoes, have doubled in production and make up a large part of the human diet but do not provide the micronutrients that are needed.  The essential nutrients that are necessary in the human diet are present in plants that rely on animal pollinators.  There have been issues in vitamin and mineral deficiencies and it is believed that if pollinator populations continue to decrease these deficiencies will become even more prominent. 
Wild pollinators often visit a large number of plant species and plants are visited by a large number of pollinator species. All these relations together form a network of interactions between plants and pollinators. Surprising similarities were found in the structure of networks consisting out of the interactions between plants and pollinators. This structure was found to be similar in very different ecosystems on different continents, consisting of entirely different species. 
The structure of plant-pollinator networks may have large consequences for the way in which pollinator communities respond to increasingly harsh conditions. Mathematical models, examining the consequences of this network structure for the stability of pollinator communities suggest that the specific way in which plant-pollinator networks are organized minimizes competition between pollinators  and may even lead to strong indirect facilitation between pollinators when conditions are harsh.  This means that pollinator species together can survive under harsh conditions. But it also means that pollinator species collapse simultaneously when conditions pass a critical point. This simultaneous collapse occurs, because pollinator species depend on each other when surviving under difficult conditions. 
Such a community-wide collapse, involving many pollinator species, can occur suddenly when increasingly harsh conditions pass a critical point and recovery from such a collapse might not be easy. The improvement in conditions needed for pollinators to recover, could be substantially larger than the improvement needed to return to conditions at which the pollinator community collapsed. 
While there are 200,000 - 350,000 different species of animals that help pollination, bees are responsible for majority of the pollination for consumed crops, providing between $235 and $577 US billion of benefits to global food production.  Since the early 1900s, beekeepers in the United States started renting out their colonies to farmers to increase the farmer's crop yields, earning additional revenue from providing privatized pollination. As of 2016, 41% of an average US beekeeper's revenue comes from providing such pollination service to farmers, making it the biggest proportion of their income, with the rest coming from sales of honey, beeswax, government subsidy, etc.  This is an example of how a positive externality, pollination of crops from beekeeping and honey-making, was successfully accounted for and incorporated into the overall market for agriculture. On top of assisting food production, pollination service provide beneficial spillovers as bees germinate not only the crops, but also other plants around the area that they are set loose to pollinate, increasing biodiversity for the local ecosystem.  There is even further spillover as biodiversity increases ecosystem resistance for wildlife and crops.  Due to their role of pollination in crop production, commercial honeybees are considered to be livestock by the US Department of Agriculture. The impact of pollination varies by crop. For example, almond production in the United States, an $11 billion industry based almost exclusively in the state of California, is heavily dependent on bees for pollination of almond trees. Almond industry uses up to 82% of the services in the pollination market. Each February, around 60% of the all bee colonies in the US are moved to California's Central Valley. 
Over the past decade, beekeepers across the US have reported that the mortality rate of their bee colonies has stayed constant at about 30% every year, making the deaths an expected cost of business for the beekeepers. While the exact cause of this phenomenon is unknown, according to the US Department of Agriculture Colony Collapse Disorder Progress Report it can be traced to factors such as pollution, pesticides, and pathogens from evidences found in areas of the colonies affected and the colonies themselves.  Pollution and pesticides are detrimental to the health of the bees and their colonies as the bees' ability to pollinate and return to their colonies are great greatly compromised.  Moreover, California's Central Valley is determined by the World Health Organization as the location of country's worst air pollution.  Almond pollinating bees, approximately 60% of the bees in the US as mentioned above, will be mixed with bees from thousands of other hives provided by different beekeepers, making them exponentially susceptible to diseases and mites that any of them could be carrying.  The deaths do not stop at commercial honeybees as there is evidence of significant pathogen spillover to other pollinators including wild bumble bees, infecting up to 35-100% of wild bees within 2 km radius of commercial pollination.  The negative externality of private pollination services is the decline of biodiversity through the deaths of commercial and wild bees.
Despite losing about a third of their workforce every year, beekeepers continue to rent out their bees to almond farms due to the high pay from the almond industry. In 2016, a colony rented out for almond pollination gave beekeepers an income of $165 per colony rented, around three times from average of other crops that use the pollination rental service.  However, a recent study published in Oxford Academic's Journal of Economic Entomology found that once the costs for maintaining bees specifically for almond pollination, including overwintering, summer management, and the replacement dying bees are considered, almond pollination is barely or not profitable for average beekeepers.