The origin and maintenance of separate sexes (dioecy) is an enduring evolutionary puzzle. Although both hermaphroditism and dioecy occur in many diverse clades, we know little about the long-term evolutionary consequences of changing sexual system.Here we find evidence for at least 133 transitions between sexual systems in mosses, representing an almost unparalleled lability in the evolution of their sexual systems. Furthermore, in contrast to predictions, the transition rate from hermaphroditism to dioecy was approximately twice as high as the reverse transition. Our results also suggest that hermaphrodites may have higher rates of diversification than dioecious mosses. These results illustrate the utility of mosses for understanding the genomic and macroevolutionary consequences of hermaphroditism and dioecy.
K E Y W O R D S :Diversification, haploid dioecy, hermaphroditism, inbreeding depression, mating system, sexual dimorphism.
Supposed syntype specimens of Frullania mexicana comprise two morphologically distinct species. One is the authentic F. mexicana, consistent with its original description in Synopsis Hepaticarum. A lectotype is designated for that species based on a specimen in C.G. Nees von Esenbeck’s herbarium, now in STR. The other was listed by F. Stephani as ‘F. mexicana’ in Species Hepaticarum, but is not that species. Rather, it is described here as new based on a specimen deposited in Stephani’s herbarium, now in G. Frullania clarkii sp. nov. differs from F. mexicana in having involute versus more or less flat dorsal lobes; a ligulate, instead of triangular to narrowly triangular proximal portion of the lobule; broadly ovate underleaves with repand margins versus obovate underleaves with plane margins; and 4-keeled versus 8–10 keeled perianth. Its closest morphological affinities are with F. laxiflora and F. planifolia.
Frullania chilcootiensis Steph. and F. hattoriana J.D. Godfrey & G. Godfrey are two morphologically similar, little known species from northwestern North America. A Frullania specimen from Washington State, U.S.A. was recently discovered to have affinities with both species. The specimen’s shoots show variability in the length of the styli, as well as the number of cells composing them; two key morphological characters previously used to differentiate F. chilcootiensis from F. hattoriana. Based on this overlap and a detailed comparison of the branching and sexuality of the type specimens, F. chilcootiensis and F. hattoriana are here considered to be conspecific, with F. chilcootiensis having priority as the older name. The range of F. chilcootiensis is expanded into western Canada and the continental United States. A lectotype is designated for F. chilcootiensis from among the syntype specimens deposited in FH and G.
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