Ontogenia e estrutura das inflorescências e flores de Bactris jacq. ex scop. (Arecaceae: Arecoideae)

Abstract

Bactris is one of the most diverse Neotropical genera within Amazonian ecosystems, and its taxonomy presents numerous nomenclatural problems that can be resolved by means of morphological data supporting the construction of a correct infrageneric classification. This study allowed us to characterize and analyze the ontogeny and structure of the inflorescences and flowers of three species within this genus with the aim of providing valuable biological information and adding characteristics of interest to the taxonomy of the group. The studied taxa were collected in the Adolpho Ducke Forest Reserve, in the green area of the Campus of the Universidade Federal do Amazonas-UFAM, and in the Science Forest of the Instituto Nacional de Pesquisas da Amazônia (INPA). Inflorescences were extracted from the leaf axils of 3-5 individuals and classified into different groups for each species to establish the stages of development. The results were analyzed in the context of palm reproduction and evolution using optical and scanning electron microscopy. The ontogenetic study revealed acropetal development of the inflorescences, the formation of a bract subtending each flower of the triad, and one for each triad, with the latter being connate in B. simplicifrons. Likewise, the centripetal development sequence of the floral parts was evident, except for the androecium in B. acanthocarpoides and B. hirta, in which it is centrifugal. The formation of the gynoecium is synascidiate at the base, simplicate at the top, and assimplicated at the apex. Additionally, the histological arrangement of each floral organ was described, and all observed appendages were characterized. Among the characters with potential diagnostic value, the following stand out: the distribution of appendages on the prophylle of B. acanthocarpoides, the presence of tector trichomes in the sepals of such species, the development of staminodes in the pistillate flowers of B. acanthocarpoides and B. simplicifrons, the type of indumentum and the morphology of the trichomes, the absence of rigid emergencies and the reduced content of phenolic compounds in B. simplicifrons, as well as the morphology of the staminal filament in this last species, the greater scleromorphism and the presence of papillous exothecium in B. hirta, the length of the stigmatic lobes, the location of the vascular bundles in the perianth pieces, the presence of epipetal stamens, the structural organization of the gynoecium, among others. The information provided on floral development, particularly of the triad, stamens, and gynoecium, and the adnation of stamens to the corolla, will be valuable for future phylogenetic analyses.