Apomixis in Systematics, Evolution and Phylogenetics of Angiosperms: Current Developments and Prospects

Apomixis, the reproduction via asexually formed seed, is taxonomically scattered in angiosperms.
\nHere we review the major developmental pathways to apomixis and the occurrences on the
\nlevel of orders and families. We provide surveys of large families for which occurrences and
\nevolutionary pathways of apomixis are well documented (Poaceae, Ranunculaceae,
\nPlumbaginaceae, Rosaceae, Brassicaceae, Rutaceae, and Asteraceae). Molecular phylogenetic,
\nphylogenomic, and cytogenetic studies have confirmed that apomixis frequently arises in
\nhybrids, with or without polyploidy. Multiple origins, different developmental pathways, and
\ngenetic/epigenetic control mechanisms confirm that apomixis is a derived trait. Pollen functions
\nare in many taxa maintained for fertilization of polar nuclei and proper endosperm development,
\nwhich allows also for maintenance of facultative sexuality and further intercrossing of lineages.
\nThis way, apomixis often results in huge and dynamic complexes of numerous hybrid genotypes
\nand phenotypes with highly reticulate relationships. Such complexes are successful to establish
\nin various habitats and geographical regions. Expression of apomixis appears to be in some
\ngenera influenced by environmental conditions. The diversity of evolutionary pathways is
\nreflected in various, genus-wise taxonomic treatments. Future research is needed to understand
\nthe short-term evolutionary dynamics, the functional background for apomixis, and the
\nlong-term evolutionary fates of apomictic lineages.