Reproductive biology and breeding system of Gonolobus suberosus (Asclepiadaceae)

We investigated the reproductive biology and breeding system of Gonolobus suberosus. Individual plants produced an average of 25.5 flowers distributed among 3.85 inflorescences, and these flowers were open and receptive to pollen for 2-10 (mean 4.61) days each. Natural levels of pollination were determined by counting the numbers of pollinaria removed and pollinia deposited for 352 flowers. Many flowers (30%) had at least one pollinarium removed, but only 4% had one or more pollinia deposited. This low rate of natural pollination probably contributed to the low fruit-set observed, as only one of the 352 flowers matured a fruit. Like most other members of the Asclepiadaceae, G. suberosus is genetically self-incompatible. Of 110 artificial cross-pollinations, 13 (11.8%) were successful, versus none of 110 artificial self-pollinations. Fluorescence microscopy revealed that self-pollen tubes grew normally and entered the micropyles of ovules within the ovary. Thus, it appears that G. suberosus possesses a late-acting form of self-incompatibility, as previously documented for several species of Asclepias.