Gender modification and resource allocation in subdioecious Wurmbea dioica (Colchicaceae)

1 Populations of subdioecious species contain female, male and cosexual plants. Here we investigate factors influencing gender expression and patterns of resource allocation among the sex phenotypes in subdioecious populations of the diminutive geophyte Wurmbea dioica (Colchicaceae) from the Australian Capital Territory, south‐east Australia. 2 Demographic studies and population comparisons of the sex phenotypes were conducted to determine their distinguishing features, and whether sex expression was labile. Comparisons of biomass allocation were made to assess whether plants with hermaphrodite flowers were larger than unisexual plants. The seed fertilities of sex phenotypes were measured and related to the sex ratio of populations. 3 Female plants exhibited canalized gender producing only ovuliferous flowers, which were smaller and less showy compared to flowers of other plants. Some male plants displayed labile gender expression, producing varying numbers of male and hermaphrodite flowers (fruiting males). Maternal investment among male plants was size‐dependent. 4 Fruiting males were significantly larger and produced more flowers than unisexual plants. At flowering, we found no evidence for changes in proportional allocation with increases in size after controlling for total biomass. At fruiting, allocation patterns differed between females and fruiting males independently of size. 5 Total seed output by fruiting males was 70% of that produced by females. The number of seeds per fruit declined acropetally in both sexes, and males produced, on average, more seeds per fruit than females. Data on the relation between female frequency and the relative seed fertilities of males and females gave a poor fit to Lloyd's (1976) genetic model predicting equilibrium female frequency. The lack of congruence probably occurs because size‐dependent gender modification in males complicates the assumptions of the model.