POPULATION-SIZE, POLLINATION AND BREEDING SYSTEM OF SILENE STOCKENII CHATER (CARYOPHYLLACEAE), AN ANNUAL GYNODIOECIOUS SPECIES OF SOUTHERN SPAIN

The distribution area, phenology, sex polymorphism, floral characteris tics and breeding system of Silene stockenii (Caryophyllaceae), a narr owly endemic annual species of southern Spain, were studied. Only five populations were found in a total area of 2 ha. Silene stockenii is a gynodioecious species with fully female, fully hermaphrodite and inte rmediate plants bearing hermaphrodite, male-sterile, and partially mal e-sterile flowers. Male-sterile flowers are typically smaller than her maphrodites. Nectar production was significantly higher in hermaphrodi te plants and during the female phase of hermaphrodite flowers. The re d flowers appear during the spring (March-May) and are pollinated by l ong-tongued Bombyliidae. Hand pollinations revealed that the species i s self-compatible; however, natural self-pollination is rare due to ma rked protandry. Hand pollination significantly increased the number of seeds per fruit and seed set, indicating limited pollination in the f ield. In controlled pollinations female plants of S. stockenii produce d higher seed set than hermaphrodite plants, but in freely pollinated plants fruit set and seed production was similar in both morphs, indic ating that pollinators do not discriminate in favour of hermaphrodite plants.