Apomixis - Apomixis and Evolution

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 congeneric apomicts, 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 aggregate species, typically listed in floras with the convention "Genus species agg." (e.g., the bramble, Rubus fruticosus agg.). In some plant families, genera with apomixis are quite common, e.g. 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), Hieracium (hawkweeds) and Taraxacum (dandelions).

Although the evolutionary advantages of sexual reproduction are lost, apomixis can pass along traits fortuitous for evolutionary fitness. As Clausen eloquently put it (page 470)

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, i.e. that "obligate apomixis" is an artifact of insufficient observation (missing uncommon sexual reproduction).