Floral Sex Ratios in Andromonoecious Umbelliferae

SUMMARY The distribution of hermaphrodite and male flowers was determined in the inflorescences of three andromonoecious species of Umbelliferae, Smyrnium olusatrum, Pastinaca sativa and Anthriscus sylvestris. Despite wide differences in the number of flowers produced per plant by the three species the floral ratio 4 male to 1 hermaphrodite was remarkably constant and except in an extreme environment 55 to 70 % of hermaphrodite flowers produced ripe seeds. The constancy in floral ratio per plant was maintained by quite different distributions of flower type between umbels in the three species. The apparent contradiction between protandry in flowers but protogyny within umbels is interpreted as an avoidance of simultaneous competition for resources within the plant.