THE REPRODUCTIVE-BIOLOGY OF VINCETOXICUM-NIGRUM (L) MOENCH (ASCLEPIADACEAE), A MEDITERRANEAN WEED IN NEW-YORK-STATE

The reproductive biology of Vincetoxicum nigrum was investigated in Du tchess County, New York. The small, dark purple flowers open in the mo rning and remain open for approximately 7 days. Although a heavy, frui ty, unpleasant scent is emitted throughout the day and night, it is st rongest 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 fruit s with viable seeds, as compared to 11.1% of 72 unbagged flowers. In a ddition, the plants are clonal, with deep roots and rhizomes. Of 50 se eds 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 mor e 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 lar ge territorial fly, Sarcophaga sp., defends flowers from visits by oth er flies.