Abstract
There is large variation in seed mass within P. oreoselinum (L.) Moench selected for the present study from two contrasting habitats: roadside and oak forest. Effect of seed position within a plant and of soil nutrients on seed mass, germination and seedlings growth were studied. Within an individual plant, seed mass decreased with umbel order and seeds from the central umbellet of the umbel were lighter than those from the outer edge, suggesting that variation in seed mass within an individual plant was due to the position effect. There was a significant relationship between seed mass and total germination. Covariate analysis showed the differences between sites in seed macronutrient contents were caused by respective differences in seed mass and soil macronutrients. This indicates substantial variation in the amount of reserves initially available for seedling growth. In conclusion, phenotypically-based variation in seed mass may arise from soil conditions, maternal traits or combination of the two. High variability in seed mass of P. oreoselinum favours its widespread geographic distribution. These results suggest that with respect to germination characteristics large seeds from primary order have a competitive advantage over small seeds produced on secondary umbels because they have higher overall germination.