Effects of Seed Size and Microsite on Seedling Emergence of Prunella Vulgaris in Four Habitats

(1) The effects of seed size and microsite characteristics on seedling emergence were examined in two woodland and two old-field habitats of Prunella vulgaris. Seeds of known size were sown in the field and subsequent seedling emergence was monitored. Characteristics of the microsites in which seedlings emerged were also noted. (2) Both seed size and microsite characteristics affected seedling emergence. In general, large seeds had a higher percentage emergence. Litter and herbaceous cover inhibited seedling emergence in woodland habitats and herbaceous cover inhibited emergence in old-field habitats. In all habitats, larger seeds had less stringent requirements. (3) Within a habitat, the magnitude of the effect of seed size on seedling emergence may be influenced by the mean size of seeds produced and the abundance of microsites favourable for germination. (4) Seed size is a phenotypically plastic characteristic in P. vulgaris. A reciprocaltransplant experiment demonstrated that, in a habitat with a high herbaceous cover, plants produced small seeds regardless of their origin. Larger seeds were produced by both transplanted and native individuals in a habitat with a low herbaceous cover.