Premise of research. Maintenance of dioecious and monoecious sexual systems at nearly equal frequencies, infrequent sexual expression, and distinctly female-skewed sex ratios among the dioecious species are reproductive characteristics of bryophytes, which are otherwise unusual among embryophytes. Most sex ratio assessments to date have relied on gametophytes forming sexual organs, and how these reflect genetic genders is largely unresolved.

Methodology. For the European wetland moss Drepanocladus lycopodioides, we ask whether the adult expressed sex ratio is more strongly female biased than the “true” population sex ratio based on genetically male and female plants, i.e., whether males exhibit a lower sex expression rate than females (shy males). We assess expressed sex ratio on the basis of sex expression in individually scored herbarium specimens. We directly and on a large geographic scale assess nonexpressed sex ratio, for the second time in a moss, by sexing individual shoots from nonexpressing specimens using a molecular sex marker.

Pivotal results. On the basis of the female and male frequencies in these two data sets and the overall proportion of expressing specimens, we estimate the European population sex ratio as 2.6 : 1 (female to male). All three sex ratios are significantly female skewed and do not significantly differ from each other, indicating that there is no gender difference in sex expression rates.

Conclusions. These results and previous data for Drepanocladus trifarius show that males are not shy in the two wetland mosses of markedly different habitats.