Seed Type and Seed Size Variation in the Heteromorphic Saltmarsh Annual Spergularia salina along the Coast of Sweden

Abstract: We investigated habitat characteristics, seed type and seed size variation between and within 41 populations of the heteromorphic saltmarsh annual Spergularia salina. 95% of the investigated populations were truly heteromorphic regarding unwinged or winged seeds but either of the seed types could dominate in individual populations. 39% of all seed capsules contained mixed seed types, in 43% of capsules the seeds were exclusively unwinged, and in 18% only winged seeds were found. In a closer survey in one of the populations (at Tullgarn, 5850'N, 1737'E), albeit predominantly heteromorphic, again capsules either contained mostly unwinged or winged seeds: 59% of the capsules had mixed contents, 21% contained exclusively unwinged seeds, and 21 % produced only winged seeds. Seed weight varied up to 10-fold, with an overall mean of 77.2μg. 27% of this variation was due to variation among populations, 52% was explained by variation between individuals, and 21% was due to variation within individuals. Seed weight was positively correlated with the frequency of winged seeds per capsule, especially within populations, and negatively correlated to seed number. The frequency of winged seeds in each capsule and seed weight was positively correlated with population density both between and within populations.