Syzygiella rubricaulis is a dioecious leafy liverwort disjunctly distributed and restricted to high-altitude mountains in the Neotropics and the Azores. This study is part of a larger project examining the phylogeography of S. rubricaulis in the Neotropics, and our main goals were to understand its reproductive biology, where sex expression occurs, if vegetative propagules are frequently found, how the sexes are distributed in populations, how frequently sporophytes are formed and what environmental conditions influence sexual expression. S. rubricaulis patches are mostly female, but all patches also contain non sex-expressing shoots. Out of 42 patches examined, 29 (69%) were sex-expressing: 25 were unisexual (21 female and four male) and four of mixed sex (two male-biased and two unbiased). At shoot level, out of 4200 shoots 18% were female and 7% male; among sex-expressing shoots, 73% were female, representing a sex ratio of 0.8 (female-biased). We encountered a total of 33 sporophytes in six patches (in Brazil, Venezuela and Ecuador). Leaf regenerants were found in one patch in Mexico. Low rates of sporophytes were likely related to low frequencies of male shoots and large distances between the sexes. As 25% of S. rubricaulis shoots expressed sex (occasionally producing sporophytes), we suggest that short-distance (and rarely long-distance) spore dispersal events occur in mountainous areas on a short-term basis. On a long-term basis, however, these events likely contribute to dynamic exchanges among populations in the Neotropics.

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