The Reproductive Biology of Asclepias Tuberosa

SUMMARY Individual flowers of the self‐incompatible milkweed Asclepias tuberosa are available to pollinators for 7 or 8 days; however, there is a large overlap in flowering time (4 to 5 weeks) within and among inflorescences on a single plant and therefore the possibility of high levels of self‐pollination. Pollinator activity closely follows availability of flowers, although the more rapid decline of the former may indicate switching of pollinators to other plant species flowering simultaneously. These observational data are combined with experimental crossing data to write probability functions for a simple multiplicative model incorporating both extrinsic and intrinsic factors determining fruit‐set. Fruit‐set predictions from the model are very close to the 033% observed in natural populations of A. tuberosa.