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In botany, apomixis was defined by Hans Winkler as replacement of the normal sexual reproduction by asexual reproduction, without fertilization. Its etymology is Greek for "away from" + "mixing". This definition notably does not mention meiosis. Thus "normal asexual reproduction" of plants, such as propagation from cuttings or leaves, has never been considered to be apomixis, but replacement of the seed by a plantlet or replacement of the flower by bulbils are 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 gymnosperms, it appears to be absent in that group.〔 Apogamy is a related term that has had various meanings over time. In plants with independent gametophytes (notably ferns), the term is still used interchangeably with "apomixis", and both refer to the formation of sporophytes by parthenogenesis of gametophyte cells. Male apomixis (paternal apomixis) involves replacement of the genetic material of the egg cell by that from the pollen. ==Apomixis and evolution== Because apomictic plants are genetically identical from one generation to the next, each lineage has some of the characters of a true species, maintaining distinctions from other apomictic lineages within the same genus, while having much smaller differences than is normal between species of most genera. They are therefore often called microspecies. In some genera, it is possible to identify and name hundreds or even thousands of microspecies, which may be grouped together as species aggregates, typically listed in floras with the convention "''Genus species'' agg." (such as the bramble, ''Rubus fruticosus'' agg.). In some plant families, genera with apomixis are quite common, for example in Asteraceae, Poaceae, and Rosaceae. Examples of apomixis can be found in the genera ''Crataegus'' (hawthorns), ''Amelanchier'' (shadbush), ''Sorbus'' (rowans and whitebeams), ''Rubus'' (brambles or blackberries), ''Poa'' (meadow grasses), ''Nardus stricta'' (Matgrass), ''Hieracium'' (hawkweeds) and ''Taraxacum'' (dandelions). Although the evolutionary advantages of sexual reproduction are lost, apomixis can pass along traits fortuitous for evolutionary fitness. As Jens Clausen put it The apomicts actually have discovered the effectiveness of mass production long before Mr Henry Ford 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). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Apomixis」の詳細全文を読む スポンサード リンク
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