The reproductive biology of Vincetoxicum nigrum (L.) Moench (Asclepiadaceae), a Mediterranean weed in New York State.

York. The small, dark purple flowers open in the morning and remain open for approximately 7 days. Although a heavy, fruity, unpleasant scent is emitted throughout the day and night, it is strongest during the day. The first flowers appear in mid-May, but peak flowering occurs in mid- to late-June, tapering off in early July. The flowers are autogamous, with 4.2% of 167 bagged flowers setting fruits with viable seeds, as compared to 1 1. 1% of 72 unbagged flowers. In addition, the plants are clonal, with deep roots and rhizomes. Of 50 seeds tested in September (without a period of dormancy) 14 germinated, versus 20 of 50 that had overwintered. Of seeds from unbagged flowers, 49% germinated versus 40% of those produced by autogamy. Although more than 14 species of flies visited the flowers of V. nigrum, only six species, representing four families, carried V. nigrum pollinia. Flies pick up pollinia on their proboscises as they probe for nectar. A large territorial fly, Sarcophaga sp., defends flowers from visits by other flies.