The evolutionary ecology (evo-eco) of plant asexual reproduction

The different modes of asexual plant reproduction are reviewed in the context of the evolutionary ecology (evo-eco) of retaining old (and colonizing new) habitats and exploring new ones. The modes of asexual reproduction are contrasted between the green algae and the nonvascular and vascular land plants (bryophytes and tracheophytes, respectively). The chronology of their appearance is also traced in the fossil record. Among bryophytes, the indeterminate growth of protonema and the subsequent fragmentation of gametophytes provide a successful asexual reproductive stratagem, one that is paralleled by indeterminate rhizomaty and subsequent fragmentation of tracheophyte sporophytes. Self-compatible (autogamous) bisexual (monoicous) gametophytes capable of producing viable homozygous sporophytes offer a method for colonizing new sites by means of a single spore, a stratagem that is paralleled in tracheophyte sporophytes by the co-option of sexual reproductive structures (e.g., flowers) to produce diploid embryos asexually (e.g., variants of apomixis such as nucellar embryony). A review of the fossil record and the biology of extant taxa show that some of these modes of asexual reproduction are ancient and present in the green ancestors of the land plants (i.e., the charophycean algae). An overview of the data indicates that asexual reproduction provides a bet-hedging stratagem that can obviate some of the many costs of sexual reproduction, and preserve well-adapted genomes within previously occupied sites.