Distyly, Floral Visitors, and Fructification in 2 Natural Populations of Psychotria nervosa (Rubiaceae)

Distyly is a common reproductive strategy in the family Rubiaceae. Studies on tropical species of the genus Psychotria present several cases of atypical distyly, e.g., the absence of reciprocal positioning of sexual organs between morphs, anisoplethy, limited pollen availability, and monomorphy. To describe the floral polymorphism and reproductive ecology of Psychotria nervosa, I studied the proportion of morphs, the floral morphology, the number of inflorescences, flowers, and fruits set between morphs, and the diversity and behaviour of floral visitors in 2 natural populations of the species in a seasonally dry tropical forest in Mexico. Psychotria nervosa is a distylous species; both populations presented a 1:1 morph ratio, with reciprocal positioning of sexual organs between morphs, as well as a suite of ancillary floral traits associated to polymorphism. The diversity and behaviour of the floral visitor assemblage caused a higher fruit set in the longstyled morph than in the short-styled morph in both populations. Furthermore, the highest fruit set was observed in the most morphologically reciprocal population.