Unisexual, female- or male-biased populations are common among dioecious bryophytes and the demographic causes of such biases are unclear. Life history studies can be valuable in understanding the contribution of each life history stage to a population sex ratio, yet few studies use this approach. We chose to study the liverwort Marchantia infexa to investigate the potential effect of various stages/traits on population sex ratio. Across M. inflexa’s distribution range, herbarium data suggest female-biased sex ratios. Field studies in Trinidad & Tobago suggest an overall 1:1 sex ratio within a single watershed, however, patches can be single-sex, bisexual or without sex expression. We investigated sex-specific survival of asexual propagules (lab), clonal expansive traits (greenhouse) and patterns of sex expression (field & greenhouse). We found that neither sex had a consistent advantage. Females had higher propagule survival, lower propagule production and higher growth rates. Sex expression tended to occur first in males then in females. These patterns suggest that focusing on any single stage or trait can result in erroneous conclusions as to the demographic causes of sex ratio biases. Thus, studies on population sex ratio biases should incorporate multiple traits and stages.

Key words: Marchantia inflexa , asexual reproduction, life history, liverwort, sex expression, sex ratio