Novelties in the floral morphoanatomy of three Psychotria L. species (Rubiaceae)

Abstract

The Psychotrieae alliance is a monophyletic group belonging to the Rubiaceae family, composed of nine tribes, with a problematic internal delimitation. The genus Psychotria L. is the most representative in the alliance, with about 2,000 species, and in the current circumscription is considered paraphyletic. Since Psychotria is morphologically uniform, the accurate circumscription of the genus is difficult to establish due to the large number of species and the absence of diagnostic characters. In this context, we studied the floral morphoanatomy of Psychotria leiocarpa Cham. & Schltdl., Psychotria carthagenensis Jacq., and Psychotria brachyceras Mull. Arg., aiming to provide informative characteristics for ongoing phylogenetic studies within the genus and the alliance. Our results showed that all species have cymose and terminal inflorescences, forming a dichasium. The anatomical structure of the floral organs demonstrated potentially informative traits, including: the presence of a set of secretory cells in the petals, raphides in the ovule integument, and papillose cells in the outer epidermis of the ovary in P. brachyceras; the presence of prismatic crystals in the ovary of P. brachyceras and P. leiocarpa; as well as the presence of non-glandular trichomes in the outer epidermis of the ovary, presence of phenolic compounds, and absence of prismatic crystals in all floral organs of P. carthagensis. Regarding the other tribes of the alliance, our results indicate that the traits related to the gynoecium seem to have more relevance in superior taxonomic categories, such as the structure of the ovary, number of ovules per locule, placentation, ovule curvature and presence/absence of an obturator. This is the first comprehensive attempt to clearly identify informative floral morphoanatomical traits among the three species of the genus. Psychotria L.