Can fruit ontogenetic features prove to be an important tool in the circumscription of Psychotrieae alliance?

Abstract

The Rubiaceae tribe Psychotrieae sensu lato and its two largest genera, Psychotria L. and Palicourea Aubl., have been considered taxonomically controversial for a long time. We aimed to identify structural features of the ontogeny of the fruits and seeds with taxonomic potential for the tribe by using species of these two genera, and Rudgea jasminoides (Cham.) Müll.Arg. The samples were obtained from a herbarium and from Brazilian state parks, and sectioned by using a rotation microtome. The fruits were found to be derived from an inferior ovary, and were characterised by a fleshy mesocarp and sclerenchymatic sinuate pyrene. The seeds were pachychalazal and arillate. The fruit was classified as a pomaceous drupoid nuculanium. The investigation showed the utility of some fruit features to discriminate species. Our study also showed that ontogenetic features of fruits and seeds are very homogeneous in Palicourea and Psychotria, which supports the inclusion of both genera in the tribe Psychotrieae.