Stuart F. McDaniel and Pierre-François Perroud (2012) Invited perspective: bryophytes as models for understanding the evolution of sexual systems. The Bryologist: Vol. 115, No. 1, pp. 1-11.
One of the first life history characters that students of bryology learn is the bryophyte life cycle. Roughly half of the bryophytes have separate sexes (dioicous) and half are hermaphroditic (monoicous). This variation is important for taxonomic purposes but also has major consequences for nearly every aspect of bryophyte biology. For example, dioicous species generally reproduce less frequently than monoicous species (Longton & Schuster 1983) but harbor more genetic variation than monoicous species (Eppley et al. 2006). More broadly, however, the maintenance of both sexual systems at nearly equal frequencies in the bryophytes is quite unusual among the eukaryotes. This situation makes bryophytes an important model system for studying the evolutionary consequences of changes in sexual system.