Duodichogamy and sex lability in Sapindaceae: the case of Paullinia weinmanniifolia

Abstract

Paullinia weinmanniifolia (Sapindaceae) is an endemic Brazilian climber found in the Atlantic Forest. The flowers are arranged in synflorescences with approximately 34 thyrses. In the studied material, each thyrse produced 85.8 male flowers and 15.8 female flowers. The small, diclinous and zygomorphic flowers present a sophisticated morphology, described here in detail. They are visited by many insects, with bees being the main pollinators. Sex expression was investigated by monitoring one population of restinga in Marica Environmental Protection Area, Rio de Janeiro State, Brazil, during 2–4 years. Experiments were conducted taking into account thyrse, synflorescence, plant and population. Most individuals showed a duodichogamic sequence of flowering (male–female–male). However, the population overall had a more complex flowering pattern: some individuals were protogynous, others protandrous; a few individuals produced flowers of only one sex, and some individuals changed sex expression in the second year of the study, either from male to female or from female to male. This was the first ever labile sex expression recorded for the tribe Paullinieae. Anthetic female and male flowers were never found simultaneously in the same thyrse or synflorescence. Nevertheless, the two flower morphs overlapped, though rarely, within the same individual. The pattern of flowering observed in this species maximizes the level of outcrossing, since the temporal separation of male and female flowers on the same plant is precise enough for the species to be regarded as (obligatorily) xenogamous.