Abstract
Based on morphological characters, Silene acaulis subsp. exscapa and Silene acaulis subsp. cenisia have been previously described as dioecious and trioecious, respectively. Here we examine whether these subspecies are truly dioecious (subsp. exscapa) and trioecious (subsp. cenisia) based on individual seed and pollen production. Nine populations of subsp. cenisia and five populations of subsp. exscapa were studied in the French Alps. The ratio of staminate to female plants within populations did not in general differ from 1:1, the sex ratio expected in dioecious populations. Staminate plants of both subspecies were found to set fruits. In subsp.exscapa, the ratio of fruit production in female versus staminate plants is around 900; in subsp. cenisia, this ratio is around 10. The advantage of female plants in fruit production is not always sufficient to explain their frequencies in natural populations. Staminate plants cannot be divided in two distinct categories: males and hermaphrodites. The two subspecies can be best described as subdioecious, although S. a. exscapa is effectively closer to exhibiting true dioecy than S. a. cenisia.