IS SILENE-ACAULIS (CARYOPHYLLACEAE) A TRIOECIOUS SPECIES - REPRODUCTIVE-BIOLOGY OF 2 SUBSPECIES

Based on morphological characters, Silene acaulis subsp. exscapa and S ilene acaulis subsp, cenisia have been previously described as dioecio us and trioecious, respectively. Here we examine whether these subspec ies are truly dioecious (subsp. exscapa) and trioecious (subsp, cenisi a) 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 popul ations did not in general differ from 1:1, the sex ratio expected in d ioecious populations. Staminate plants of both subspecies were found t o set fruits. In subsp. exscapa, the ratio of fruit production in fema le versus staminate plants is around 900; in subsp. cenisia, this rati o is around 10. The advantage of female plants in fruit production is not always sufficient to explain their frequencies in natural populati ons. Staminate plants cannot be divided in two distinct categories: ma les and hermaphrodites. The two subspecies can be best described as su bdioecious, although S, a. exscapa is effectively closer to exhibiting true dioecy than S. a. cenisia.