Sex ratio patterns in dioicous bryophytes re-visited

Abstract

Based on a literature survey and our own investigations of selected species, we present a compilation of expressed sex ratios in 103 taxa of dioicous bryophytes, including 56 mosses and 47 liverworts. We grouped the approaches used to determine sex into two categories: (1) sex assessment per herbarium specimen or per patch in the field; (2) sex assessment by examination of individual shoots or thalli, usually in the field. Eighty-eight per cent of the taxa studied by the former methods, and 68% of those included in the latter, exhibited a female-biased sex ratio. The F : M values varied by a factor of 46 among species, excluding cases with only one sex expressing. There was also within-species variation of sex expression and ratio related to geographical area, altitude, year, substratum, plant maturity, and compared with cultivation conditions, and between the two method categories. Across taxa, proportions of non-expressing and sporophytic samples were negatively related to each other; however, there was no significant relationship between sex ratio and the proportion of sporophytic samples or shoots. The present data do not support the generalization that the most strongly female-biased sex ratios among dioicous bryophytes occur in 'extreme environments'. On the other hand, it is suggested here that phylogenetic history may explain observed species-wide sex ratios better than current habitat conditions in at least some cases.