Self‐incompatibility Systems in the Rubiaceae of a Tropical Lowland Wet Forest

A program of experimental field pollinations was carried out on 14 species of woody Rubiaceae in a Costa Rican wet forest in order to test for the presence of self‐incompatibility systems. Species of Cephaelis, Coussarea, Faramea, Hamelia, Posoqueria, Psychotria, Rudgea, and Warszewiczia were investigated in the study. Ten of the species are distylous, and of these, nine were found to be self‐incompatible. The site of the incompatibility barrier varied between and within species. Short style plants always had stigmatic inhibition of pollen tubes following self and intraform pollinations, but the site of the rejection response in long style plants was quite variable. In several species, pollen tubes, resulting from incompatible pollinations of the long style flowers, penetrated to the base of the style. Fruit set was followed in two of these species, and despite deep penetration of self and intraform pollen tubes in the long style morph, only interform pollinations resulted in fruit set. Four of the species tested are florally monomorphic and each was found to be self‐incompatible on the basis of fruit set patterns. Pollen tubes in the styles of self‐pollinated flowers of two of the monomorphic species, penetrated to the ovary, but no fruits resulted from selfpollinations.