![Poa bulbosa, vegetative apomixis](https://upload.wikimedia.org/wikipedia/commons/7/70/Poa_bulbosa%2C_vegetative_apomixis.jpg)
In
botany
Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the Ancient Greek w ...
, apomixis is
asexual reproduction
Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the fu ...
without fertilization. Its etymology is Greek for "away from" + "mixing". This definition notably does not mention
meiosis
Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately resu ...
. Thus "normal
asexual reproduction
Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the fu ...
" of plants, such as propagation from cuttings or leaves, has never been considered to be apomixis, but replacement of the seed by a
plantlet
A plantlet is a young or small plant."Plantlet", Merriam-Webster'
Many plants such as spider plants naturally create stolons with plantlets on the ends as a form of asexual reproduction. Vegetative propagules or clippings of mature plants may ...
or replacement of the flower by
bulbils
A bulbil (also referred to as bulbel, bulblet, and/or pup) is a small, young plant that is reproduced vegetatively from axillary buds on the parent plant's stem or in place of a flower on an inflorescence. These young plants are clones of the p ...
were categorized as types of apomixis. Apomictically produced offspring are genetically identical to the parent plant.
Some authors included all forms of asexual reproduction within apomixis, but that generalization of the term has since died out.
In flowering plants, the term "apomixis" is commonly used in a restricted sense to mean agamospermy, i.e.,
clonal reproduction through seeds. Although agamospermy could theoretically occur in
gymnosperm
The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers, cycads, ''Ginkgo'', and gnetophytes, forming the clade Gymnospermae. The term ''gymnosperm'' comes from the composite word in el, γυμνό ...
s, it appears to be absent in that group.
[
Apogamy is a related term that has had various meanings over time. In plants with independent ]gametophyte
A gametophyte () is one of the two alternation of generations, alternating multicellular organism, multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has on ...
s (notably ferns), the term is still used interchangeably with "apomixis", and both refer to the formation of sporophyte
A sporophyte () is the diploid multicellular stage in the life cycle of a plant or alga which produces asexual spores. This stage alternates with a multicellular haploid gametophyte phase.
Life cycle
The sporophyte develops from the zygote pr ...
s by parthenogenesis
Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and development ...
of gametophyte cells.
Male apomixis (paternal apomixis) involves replacement of the genetic material of an egg by the genetic material of the pollen.
Evolution
Because apomictic plants are genetically identical from one generation to the next, each lineage has some of the characters of a true species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
, maintaining distinctions from other apomictic lineages within the same genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
, while having much smaller differences than is normal between species of most genera. They are therefore often called microspecies
In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...
. In some genera, it is possible to identify and name hundreds or even thousands of microspecies, which may be grouped together as species aggregate
In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...
s, typically listed in flora
Flora is all the plant life present in a particular region or time, generally the naturally occurring (indigenous) native plants. Sometimes bacteria and fungi are also referred to as flora, as in the terms '' gut flora'' or '' skin flora''.
E ...
s with the convention "''Genus species'' agg." (such as the bramble
A bramble is any rough, tangled, prickly shrub, usually in the genus ''Rubus'', which grows blackberries, raspberries, or dewberries. "Bramble" is also used to describe other prickly shrubs, such as roses (''Rosa'' species). The fruits inclu ...
, ''Rubus fruticosus'' agg.). In some plant families
Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclu ...
, genera with apomixis are quite common, for example in Asteraceae
The family Asteraceae, alternatively Compositae, consists of over 32,000 known species of flowering plants in over 1,900 genera within the order Asterales. Commonly referred to as the aster, daisy, composite, or sunflower family, Compositae w ...
, Poaceae
Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns an ...
, and Rosaceae
Rosaceae (), the rose family, is a medium-sized family of flowering plants that includes 4,828 known species in 91 genera.
The name is derived from the type genus ''Rosa''. Among the most species-rich genera are ''Alchemilla'' (270), ''Sorbus ...
. Examples of apomixis can be found in the genera ''Crataegus
''Crataegus'' (), commonly called hawthorn, quickthorn, thornapple, Voss, E. G. 1985. ''Michigan Flora: A guide to the identification and occurrence of the native and naturalized seed-plants of the state. Part II: Dicots (Saururaceae–Cornacea ...
'' (hawthorns), '' Amelanchier'' (shadbush), ''Sorbus
''Sorbus'' is a genus of over 100 species of trees and shrubs in the rose family, Rosaceae. Species of ''Sorbus'' (''s.l.'') are commonly known as whitebeam, rowan ( mountain-ash) and service tree. The exact number of species is disputed depend ...
'' (rowan
The rowans ( or ) or mountain-ashes are shrubs or trees in the genus ''Sorbus
''Sorbus'' is a genus of over 100 species of trees and shrubs in the rose family, Rosaceae. Species of ''Sorbus'' (''s.l.'') are commonly known as whitebeam, r ...
s and whitebeam
The whitebeams are members of the family Rosaceae, comprising subgenus ''Aria'' (or, according to some authorities, its own genus) of genus ''Sorbus'', and hybrids involving species of this subgenus and members of subgenera ''Sorbus'', ''Torminar ...
s), ''Rubus
''Rubus'' is a large and diverse genus of flowering plants in the rose family, Rosaceae, subfamily Rosoideae, with over 1,350 species.
Raspberries, blackberries, and dewberries are common, widely distributed members of the genus. Most of these ...
'' (brambles or blackberries), '' Poa'' (meadow grass
''Poa'' is a genus of about 570 species of grasses, native to the temperate regions of both hemispheres. Common names include meadow-grass (mainly in Europe and Asia), bluegrass (mainly in North America), tussock (some New Zealand species), a ...
es), ''Nardus stricta
''Nardus'' is a genus of plants belonging to the grass family, containing the single species ''Nardus stricta'', known as matgrass. It is placed in its own tribe Nardeae within the subfamily Pooideae. The name derives from ancient Greek ' () from ...
'' ( Matgrass), ''Hieracium'' (hawkweed
''Hieracium'' (),
known by the common name hawkweed and classically as (from ancient Greek ιεράξ, 'hawk'),
is a genus of flowering plant in the family Asteraceae, and closely related to dandelion (''Taraxacum''), chicory ('' Cichorium'') ...
s) and ''Taraxacum'' (dandelion
''Taraxacum'' () is a large genus of flowering plants in the family Asteraceae, which consists of species commonly known as dandelions. The scientific and hobby study of the genus is known as taraxacology. The genus is native to Eurasia and Nor ...
s). Apomixis is reported to occur in about 10% of globally extant fern
A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes except t ...
s.[Hong-Mei Liu, Robert J. Dyer, Zhi-You Guo, Zhen Meng,Jian-Hui Li, and Harald Schneider. (2012) The Evolutionary Dynamics of Apomixis in Ferns: A Case Study from Polystichoid Ferns. Journal of Botany Volume 2012 Article ID 510478, 11 pages https://dx.doi.org/10.1155/2012/510478] Among polystichoid ferns, apomixis evolved several times independently in three different clade
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
s.
Although the evolution
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
ary advantages of sexual reproduction
Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...
are lost, apomixis can pass along traits fortuitous for evolutionary fitness. As Jens Clausen
Jens Christen (Christian) Clausen (March 11, 1891 – November 22, 1969) was a Danish-American botanist, geneticist, and ecologist. He is considered a pioneer in the field of ecological and evolutionary genetics of plants.
Biography
Clausen wa ...
put it:The apomicts actually have discovered the effectiveness of mass production long before Mr. Henry Ford
Henry Ford (July 30, 1863 – April 7, 1947) was an American industrialist, business magnate, founder of the Ford Motor Company, and chief developer of the assembly line technique of mass production. By creating the first automobile that mi ...
applied it to the production of the automobile. ... Facultative apomixis ... does not prevent variation; rather, it multiplies certain varietal products.
Facultative apomixis means that apomixis does not always occur, i.e., sexual reproduction can also happen. It appears likely that all apomixis in plants is facultative; in other words, that "obligate apomixis" is an artifact of insufficient observation (missing uncommon sexual reproduction).
Apogamy and apospory in non-flowering plants
The gametophytes of bryophyte
The Bryophyta s.l. are a proposed taxonomic division containing three groups of non-vascular land plants (embryophytes): the liverworts, hornworts and mosses. Bryophyta s.s. consists of the mosses only. They are characteristically limited in ...
s, and less commonly fern
A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes except t ...
s and lycopods
Lycopodiopsida is a class of vascular plants known as lycopods, lycophytes or other terms including the component lyco-. Members of the class are also called clubmosses, firmosses, spikemosses and quillworts. They have dichotomously branching s ...
can develop a group of cells that grow to look like a sporophyte of the species but with the ploidy
Ploidy () is the number of complete sets of chromosomes in a cell (biology), cell, and hence the number of possible alleles for Autosome, autosomal and Pseudoautosomal region, pseudoautosomal genes. Sets of chromosomes refer to the number of mat ...
level of the gametophyte, a phenomenon known as apogamy. The sporophytes of plants of these groups may also have the ability to form a plant that looks like a gametophyte but with the ploidy level of the sporophyte, a phenomenon known as apospory.
See also androgenesis and androclinesis described below, a type of male apomixis that occurs in a conifer, ''Cupressus dupreziana
''Cupressus dupreziana'', the Saharan cypress, or tarout, is a very rare coniferous tree native to the Tassili n'Ajjer mountains in the central Sahara desert, southeast Algeria, where it forms a unique population of trees hundreds of kilometres f ...
''.
In flowering plants (angiosperms)
Agamospermy, asexual reproduction through seeds, occurs in flowering plants through many different mechanisms[ and a simple ]hierarchical
A hierarchy (from Greek: , from , 'president of sacred rites') is an arrangement of items (objects, names, values, categories, etc.) that are represented as being "above", "below", or "at the same level as" one another. Hierarchy is an important ...
classification of the different types is not possible. Consequently, there are almost as many different usages of terminology for apomixis in angiosperms as there are authors on the subject. For English speakers, Maheshwari 1950[Maheshwari, P. 1950. An introduction to the embryology of the angiosperms. McGraw-Hill, New York.] is very influential. German speakers might prefer to consult Rutishauser 1967.[Rutishauser, A. 1969. Embryologie und Fortpflanzungsbiologie der Angiospermen: eine Einführung. Springer-Verlag, Wien.] Some older text books on the basis of misinformation (that the egg cell in a meiotically unreduced gametophyte can never be fertilized) attempted to reform the terminology to match the term parthenogenesis
Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and development ...
as it is used in zoology
Zoology ()The pronunciation of zoology as is usually regarded as nonstandard, though it is not uncommon. is the branch of biology that studies the Animal, animal kingdom, including the anatomy, structure, embryology, evolution, Biological clas ...
, and this continues to cause much confusion.
Agamospermy occurs mainly in two forms: In ''gametophytic apomixis'', the embryo
An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...
arises from an unfertilized egg cell (i.e. by parthenogenesis) in a gametophyte
A gametophyte () is one of the two alternation of generations, alternating multicellular organism, multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has on ...
that was produced from a cell that did not complete meiosis. In ''adventitious embryony'' (sporophytic apomixis), an embryo is formed directly (not from a gametophyte) from nucellus
In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. It consists of three parts: the ''integument'', forming its outer layer, the ''nucellus'' (or remnant of the megasporangium), and the fe ...
or integument tissue (see nucellar embryony
Nucellar embryony (notated Nu+) is a form of seed reproduction that occurs in certain plant species, including many citrus varieties. Nucellar embryony is a type of apomixis, where eventually nucellar embryos from the nucellus tissue of the ovule ...
).
Types in flowering plants
Maheshwari[ used the following simple classification of types of apomixis in flowering plants:
*Nonrecurrent apomixis: In this type "the megaspore mother cell undergoes the usual meiotic divisions and a haploid embryo sac ]megagametophyte
A gametophyte () is one of the two alternating multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has one set of chromosomes. The gametophyte is the ...
is formed. The new embryo may then arise either from the egg (haploid parthenogenesis) or from some other cell of the gametophyte (haploid apogamy)." The haploid plants have half as many chromosomes
A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...
as the mother plant, and "the process is not repeated from one generation to another" (which is why it is called nonrecurrent). See also parthenogenesis and apogamy below.
*Recurrent apomixis, is now more often called gametophytic apomixis: In this type, the megagametophyte has the same number of chromosomes as the mother plant because meiosis was not completed. It generally arises either from an archesporial cell or from some other part of the nucellus
In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. It consists of three parts: the ''integument'', forming its outer layer, the ''nucellus'' (or remnant of the megasporangium), and the fe ...
.
*Adventive embryony, also called sporophytic apomixis, sporophytic budding, or nucellar embryony
Nucellar embryony (notated Nu+) is a form of seed reproduction that occurs in certain plant species, including many citrus varieties. Nucellar embryony is a type of apomixis, where eventually nucellar embryos from the nucellus tissue of the ovule ...
: Here there may be a megagametophyte in the ovule
In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. It consists of three parts: the ''integument'', forming its outer layer, the ''nucellus'' (or remnant of the megasporangium), and the fe ...
, but the embryos do not arise from the cells of the gametophyte; they arise from cells of nucellus or the integument. Adventive embryony is important in several species of ''Citrus
''Citrus'' is a genus of flowering plant, flowering trees and shrubs in the rue family, Rutaceae. Plants in the genus produce citrus fruits, including important crops such as Orange (fruit), oranges, Lemon, lemons, grapefruits, pomelos, and lim ...
'', in ''Garcinia
''Garcinia'' is a genus of flowering plants in the family Clusiaceae native to Asia, America, Australia, tropical and southern Africa, and Polynesia. The number of species is disputed; Plants of the World Online (POWO) recognise up to 400. Common ...
'', ''Euphorbia dulcis
''Euphorbia dulcis'', sweet spurge, is a species in the genus ''Euphorbia
''Euphorbia'' is a very large and diverse genus of flowering plants, commonly called spurge, in the family Euphorbiaceae. "Euphorbia" is sometimes used in ordinary Eng ...
'', ''Mangifera indica
''Mangifera indica'', commonly known as mango, is a species of flowering plant in the family Anacardiaceae. It is a large fruit tree, capable of growing to a height of . There are two distinct genetic populations in modern mangoesthe "Indian type ...
'' etc.
*Vegetative apomixis: In this type "the flowers are replaced by bulbils
A bulbil (also referred to as bulbel, bulblet, and/or pup) is a small, young plant that is reproduced vegetatively from axillary buds on the parent plant's stem or in place of a flower on an inflorescence. These young plants are clones of the p ...
or other vegetative propagules which frequently germinate while still on the plant". Vegetative apomixis is important in ''Allium
''Allium'' is a genus of monocotyledonous flowering plants that includes hundreds of species, including the cultivated onion, garlic, scallion, shallot, leek, and chives. The generic name ''Allium'' is the Latin word for garlic,Gledhill, Davi ...
'', ''Fragaria
''Fragaria'' () is a genus of flowering plants in the rose family, Rosaceae, commonly known as strawberries for their edible fruits. There are more than 20 described species and many hybrids and cultivars. The most common strawberries grown com ...
'', ''Agave
''Agave'' (; ; ) is a genus of monocots native to the hot and arid regions of the Americas and the Caribbean, although some ''Agave'' species are also native to tropical areas of North America, such as Mexico. The genus is primarily known for ...
'', and some grasses, among others.
Types of gametophytic apomixis
Gametophytic apomixis in flowering plants develops in several different ways.[Nogler, G.A. 1984. Gametophytic apomixis. In Embryology of angiosperms. Edited by B.M. Johri. Springer, Berlin, Germany. pp. 475–518.] A megagametophyte develops with an egg cell within it that develops into an embryo through parthenogenesis
Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and development ...
. The central cell of the megagametophyte may require fertilization to form the endosperm
The endosperm is a tissue produced inside the seeds of most of the flowering plants following double fertilization. It is triploid (meaning three chromosome sets per nucleus) in most species, which may be auxin-driven. It surrounds the embryo and ...
, pseudogamous gametophytic apomixis, or in autonomous gametophytic apomixis endosperm fertilization is not required.
*In diplospory (also called generative apospory), the megagametophyte arises from a cell of the archesporium.
* In apospory (also called somatic apospory), the megagametophyte arises from some other (somatic) cell of the nucellus.
Considerable confusion has resulted because diplospory is often defined to involve the megaspore mother cell
A megaspore mother cell, or megasporocyte, is a Ploidy, diploid cell in plants in which meiosis will occur, resulting in the production of four Diploidy#Haploid_and_monoploid, haploid megaspores. At least one of the spores develop into haploid fema ...
only, but a number of plant families have a multicellular archesporium and the megagametophyte could originate from another archesporium cell.
Diplospory is further subdivided according to how the megagametophyte forms:
* ''Allium
''Allium'' is a genus of monocotyledonous flowering plants that includes hundreds of species, including the cultivated onion, garlic, scallion, shallot, leek, and chives. The generic name ''Allium'' is the Latin word for garlic,Gledhill, Davi ...
odorum''–''A. nutans'' type. The chromosomes double (endomitosis) and then meiosis proceeds in an unusual way, with the chromosome copies pairing up (rather than the original maternal and paternal copies pairing up).
* ''Taraxacum
''Taraxacum'' () is a large genus of flowering plants in the family Asteraceae, which consists of species commonly known as dandelions. The scientific and hobby study of the genus is known as taraxacology. The genus is native to Eurasia and Nor ...
'' type: Meiosis I fails to complete, meiosis II creates two cells, one of which degenerates; three mitotic divisions form the megagametophyte.
* ''Ixeris
''Ixeris'' is a genus of Asian flowering plants in the family Asteraceae.
Concepts of which species should be included in the genus have changed in recent years because of the use of molecular investigations. Numerous species formerly regarded a ...
'' type: Meiosis I fails to complete; three rounds of nuclear division occur without cell-wall formation; wall formation then occurs.
* ''Blumea
''Blumea'' is a genus of flowering plants of the family Asteraceae.
Characteristics
Genus ''Blumea'' is found in the tropical and sub-tropical zones of Asia, especially the Indian Subcontinent and Southeast Asia. A few species are found in Aust ...
''–'' Elymus'' types: A mitotic division is followed by degeneration of one cell; three mitotic divisions form the megagametophyte.
* ''Antennaria
''Antennaria'' is a genus of dioecious perennial herbs in the family Asteraceae, native to temperate regions of the Northern Hemisphere, with a few species (''A. chilensis'', ''A. linearifolia'', ''A. sleumeri'') in temperate southern South A ...
''–''Hieracium
''Hieracium'' (),
known by the common name hawkweed and classically as (from ancient Greek ιεράξ, 'hawk'),
is a genus of flowering plant in the family Asteraceae, and closely related to dandelion (''Taraxacum''), chicory ('' Cichorium'') ...
'' types: three mitotic divisions form the megagametophyte.
* ''Eragrostis
''Eragrostis'' is a large and widespread genus of plants in the grass family, found in many countries on all inhabited continents and many islands.
''Eragrostis'' is commonly known as lovegrass or canegrass. The name of the genus is derived fr ...
''–''Panicum
''Panicum'' (panicgrass) is a large genus of about 450 species of grasses native throughout the tropical regions of the world, with a few species extending into the northern temperate zone. They are often large, annual or perennial grasses, growi ...
'' types: Two mitotic division give a 4-nucleate megagametophyte, with cell walls to form either three or four cells.
Incidence in flowering plants
Apomixis occurs in at least 33 families of flowering plants, and has evolved multiple times from sexual relatives. Apomictic species or individual plants often have a hybrid origin, and are usually polyploid.[
In plants with both apomictic and meiotic embryology, the proportion of the different types can differ at different times of year,][ and ]photoperiod
Photoperiodism is the physiological reaction of organisms to the length of night or a dark period. It occurs in plants and animals. Plant photoperiodism can also be defined as the developmental responses of plants to the relative lengths of light a ...
can also change the proportion.[ It appears unlikely that there are any truly completely apomictic plants, as low rates of sexual reproduction have been found in several species that were previously thought to be entirely apomictic.][
The genetic control of apomixis can involve a single genetic change that affects all the major developmental components, formation of the megagametophyte, parthenogenesis of the egg cell, and endosperm development.] However, the timing of the various developmental processes is critical to successful development of an apomictic seed, and the timing can be affected by multiple genetic factors.[
]
Some related terms
* Apomeiosis: "Without meiosis"; usually meaning the production of a meiotically unreduced gametophyte.
* Parthenogenesis: Development of an embryo directly from an egg cell without fertilization is called parthenogenesis. It is of two types:
**Haploid parthenogenesis: Parthenogenesis of a normal haploid
Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...
egg (a meiotically reduced egg) into an embryo is termed haploid parthenogenesis. If the mother plant was diploid, then the haploid embryo that results is monoploid
Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respective ...
, and the plant that grows from the embryo is sterile. If they are not sterile, they are sometimes useful to plant breeders (especially in potato breeding, see dihaploidy). This type of apomixis has been recorded in ''Solanum nigrum
''Solanum nigrum'', the European black nightshade or simply black nightshade or blackberry nightshade, is a species of flowering plant in the genus ''Solanum'', native to Eurasia and introduced in the Americas, Australasia, and South Africa. Ripe ...
'', ''Lilium
''Lilium'' () is a genus of herbaceous flowering plants growing from bulbs, all with large prominent flowers. They are the true lilies. Lilies are a group of flowering plants which are important in culture and literature in much of the world. M ...
'' spp., '' Orchis maculata'', ''Nicotiana tabacum
''Nicotiana tabacum'', or cultivated tobacco, is an annually grown herbaceous plant of the ''Nicotiana'' genus. The plant is tropical in origin, is commonly grown throughout the world, and is often found in cultivation. It grows to heights bet ...
'', etc.
**Diploid parthenogenesis: When the megagametophyte develops without completing meiosis, so that the megagametophyte and all cells within it are meiotically unreduced (a.k.a. diploid, but diploid is an ambiguous term), this is called diploid parthenogenesis, and the plant that develops from the embryo will have the same number of chromosomes as the mother plant. Diploid parthenogenesis is a component process of gametophytic apomixis (see above).
* Androgenesis and androclinesis are synonyms. These terms are used for two different processes that both have the effect of producing an embryo that has "male inheritance".
:The first process is a natural one. It may also be referred to as male apomixis or paternal apomixis. It involves fusion of the male and female gametes and replacement of the female nucleus by the male nucleus. This has been noted as a rare phenomenon in many plants (e.g. ''Nicotiana
''Nicotiana'' () is a genus of herbaceous plants and shrubs in the Family (biology), family Solanaceae, that is Native plant, indigenous to the Americas, Australia, Southwestern Africa and the South Pacific. Various ''Nicotiana'' species, common ...
'' and ''Crepis
''Crepis'', commonly known in some parts of the world as hawksbeard or hawk's-beard (but not to be confused with the related genus ''Hieracium'' with a similar common name), is a genus of annual and perennial flowering plants of the family Aster ...
''), and occurs as the regular reproductive method in the Saharan Cypress, ''Cupressus dupreziana
''Cupressus dupreziana'', the Saharan cypress, or tarout, is a very rare coniferous tree native to the Tassili n'Ajjer mountains in the central Sahara desert, southeast Algeria, where it forms a unique population of trees hundreds of kilometres f ...
''. Recently, the first example of natural androgenesis in a vertebrate, a fish, Squalius alburnoides
''Squalius alburnoides'' is a species of fish in the family Cyprinidae. It is found in Portugal and Spain. Its natural habitats are rivers and intermittent rivers. It may be threatened by habitat loss.
This species is a highly peculiar fish in r ...
was discovered. It is also known in invertebrates, particularly clams in the genus Corbicula
''Corbicula'' is a genus of freshwater and brackish water clams, Aquatic animal, aquatic bivalve mollusks in the family Cyrenidae, the basket clams.Gofas, S. (2015). Cyrenidae Gray, 1847. In: MolluscaBase (2015). Accessed through: World Registe ...
, and these asexually reproducing males are noted to have a wider range than their noninvasive non-hermaphroditic cousins, more similar to hermaphroditic invasive species in the genus, indicating that this does sometimes have evolutionary benefits.
:The second process that is referred to as androgenesis or androclinesis involves (artificial) culture of haploid plants from anther
The stamen (plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium., p. 10
Morphology and terminology
A stamen typically consists of a stalk called the filam ...
tissue or microspores
Microspores are land plant spores that develop into male gametophytes, whereas megaspores develop into female gametophytes. The male gametophyte gives rise to sperm cells, which are used for fertilization of an egg cell to form a zygote. Megaspor ...
. Androgenesis has also been artificially induced in fish.
*Apogamy: Although this term was (before 1908) used for other types of apomixis, and then discarded as too confusing, it is still sometimes used when an embryo develops from a cell of the megagametophyte other than the egg cell. In flowering plants, the cells involved in apogamy would be synergids or antipodal cells.
*Addition hybrids, called BIII hybrids by Rutishauser:[ An embryo is formed after a meiotically unreduced egg cell is fertilized. The ploidy level of the embryo is therefore higher than that of the mother plant. This process occurs in some plants that are otherwise apomictic, and may play a significant role in producing tetraploid plants from triploid apomictic mother plants (if they receive pollen from diploids). Because fertilization is involved, this process does not fit the definition of apomixis.
*]Pseudogamy Pseudogamy refers to aspects of reproduction. It has different (but related) meanings in zoology and in botany.
In zoology
In zoology it means a type of parthenogenesis in which the sperm stimulates the egg cell to develop into an embryo, but no ...
refers to any reproductive process that requires pollination
Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by wind. Pollinating agents can be animals such as insects, birds ...
but does not involve male inheritance. It is sometimes used in a restrictive sense to refer to types of apomixis in which the endosperm
The endosperm is a tissue produced inside the seeds of most of the flowering plants following double fertilization. It is triploid (meaning three chromosome sets per nucleus) in most species, which may be auxin-driven. It surrounds the embryo and ...
is fertilized but the embryo
An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...
is not. A better term for the restrictive sense is centrogamy.[
*Agamospecies, the concept introduced by ]Göte Turesson
Göte Wilhelm Turesson (6 April 1892 – 30 December 1970) was a Swedish evolutionary botanist who made significant contributions to ecological genetics, and coined the terms ecotype and agamospecies. He conducted extensive work to demonstra ...
: "an apomict population the constituents of which, for morphological, cytological or other reasons, are to be considered as having a common origin," i.e., basically synonymous with "microspecies.[Defining species: a sourcebook from antiquity to today, by John S. Wilkins, , 2009]
pp. 122, 194
/ref>
See also
* , a process of nuclear fusion that occurs during pollen meiosis
* , a phenomenon known in zoology where mating with another taxon is required to complete reproduction
*
* , the production of seedless fruits
* , the animal equivalent of apomixis
*
References
Further reading
* Gvaladze G.E. (1976). Forms of Apomixis in the genus ''Allium'' L. In: S.S. Khokhlov (Ed.): Apomixis and Breeding, Amarind Pub., New Delhi-Bombay-Calcutta-New York pp. 160–165
* Bhojwani S.S.& Bhatnagar S.P. (1988). The Embryology of angiosperms. Vikas Publishing house Pvt.Ltd. New Delhi.
* Heslop-Harrison, J. (1972) "Sexuality in Angiosperms,"pp. 133–289, In Steward,F.C. (ed.) Plant Physiology, Vol. 6C, Academic Press New York.
External links
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Plant reproduction
Asexual reproduction