Seed dimorphism and germination behaviour in Salicornia patula

One of the annual species of the genus Salicornia from the Mediterranean coast, Salicornia patula presents a seed dimorphism. This morphological seed dimorphism is linked with a physiological ‘dimorphism’ with regard to some requirements for germination. Central seeds, in the inflorescence, are larger, are dispersed attached to the perianth, have no light requirement for germination and seem to have a low germination response to salinity. The lateral seeds, which are free from perianth envelopes, require light and cold pretreatment and seem to have a high sensitivity to salinity. Salicornia patula colonizes unstable transition zones between permanently flooded muds and perennial vegetation. These zones have a winter flooding period. The beginning of the flooding period and of the dry period may vary from year to year, depending on the erratic distribution of autumn and winter rains on the Mediterranean coast. So, in some years, a seedling population may be destroyed before reaching the stage of seed production. Seed dimorphism might cause germination to the more distributed in time, thus reducing the chances of extinction of a complete generation. In the present paper salinity and temperature response are described more precisely, are investigated, some aspects of the longevity of the two types of seed, and the adaptative significance of the corresponding dispersal and germination syndromes are discussed in more detail.