In the liverwort Marchantia inflexa, sex-specific differences in life histories were documented in greenhouse-grown plants. Such sex-specific life history patterns can lead to biased population sex ratios as seen in the field. Greenhouse and field conditions are likely to differ and sex-specific differences might be dependent on environmental conditions. Therefore, we undertook a study to test for sex specific differences in life histories of M. inflexa in the field across relevant environmental variation. Along a river in a tropical rain forest in Trinidad, plants likely to be male and plants likely to be female were collected and planted on ten plots (40 cm x 60 cm) cleared of other M. inflexa plants. Twenty plants of each sex were randomly planted per plot. Canopy photos (180 degree) were taken above each plot. Analysis of these photos allowed us to categorize each plot as a low, medium or high light plot. Data were taken on initial plant size, and after six months we recorded final size, number of cups (structures that produce asexual propagules) and number of growing tips (analogous to shoots) of each plant. Females and males did not differ in any of the three response variables. However, there was a strong light effect where plants had greater growth, produced more cups and produced more growing tips in high light compared to low light. The lack of sex-specific differences in life history traits might be due to the slower growth rates in the field compared to the greenhouse. Plants grew approximately three times faster in the greenhouse than in the field, and sex-specific differences became evident after three months of greenhouse growth.

Key words: bryophytes, Marchantia inflexa, sex-specific life history traits