Abstract
Distylous species have populations with two floral morphs. The pin morph has long pistils and short stamens while the thrum morph presents short pistils and long stamens. Usually heterostylous plants present a diallelic system of incompatibility and morphs occur in a 1:1 ratio (isoplethy) in the populations. Different forms of variations occur in distylous species, such as the presence of self-compatibility, anisoplethy and variation in the reciprocity level between anthers and stigmas of the two floral morphs. The aim of this study was to investigate the occurrence of the distylous characteristics in two Rubiaceae species. For this purpose, morph ratio, reciprocal herkogamy, incompatibility system and flower visitors of Psychotria deflexa and Declieuxia fruticosa were studied. Both species have the two floral morphs in equal ratio, high reciprocity values for height of the reproductive whorls of the floral morphs and were visited only by insects. However, the thrum morph on both species presented partial self-incompatibility. Within the Rubiaceae, even in distinct phylogenetic groups, weakening or breakdown of distyly seems to occur in similar patterns, but deviations in the incompatibility system have been mostly recorded for the pin morph of distylous species. In the studied species the populations had equal morph ratio despite the pseudocompatibility of the thrum morph, which indicates that factors such as high reciprocal herkogamy and possibly efficient pollination services could promote the maintenance of distyly in these species.
Key words:
heterostyly; isoplethy; floral polymorphism; pollination; incompatibility system
