Morfologia e anatomia dos apêndices petalares na tribo Schwenckieae (Solanaceae)

Abstract

Schwenckieae (Solanaceae) is a small tribe with neotropical distribution, represented by three genera, Schwenckia, Melananthus and Heteranthia, group containing approximately 31 species. It is the only tribe of Solanaceae characterized morphologically by appendices in the corolla. The flowers of most species of this tribe typically have petals with emarginated limbo, with two lateral lobules and a central lobule here called appendix, which varies in size and shape. The presence of the appendices of the corolla is considered an important taxonomic characteristic, but its function is still unknown. The floral feature, such as tube-shaped corolla, flower opening at night and odor, suggest the pollination performed by moths and that the appendices are involved in the process, acting as perfume-secreting structures (osmophores), hypothesis tested here. Currently, we investigated the micromorphology and anatomy of four species of Schwenckia, S. americana (and two varieties), S. angustifolia, S. curviflora and S. novaveneciana, and one species of Melananthus, M. fasciculatus. The appendices have secretory characteristics, with uniseriate rough glandular epidermis, absence of stomata, anficrival vascular bundle, with more developed phloematic than xylematic portion, and parenchymatic tissue with starch grains, which are consumed in the anthesis stage. The sensorial test indicated a strong and sweet odor. The anatomical analysis evidenced that this odor originated not only from the appendices, but also from the corolla lateral lobules that have papillary glandular surface. S. americana var. americana is the only taxa without odor, which nevertheless maintained the metabolic activity in the appendices, evidenced by neutral red. The presence of volatile compounds, such as essential oils and phenolic compounds, are being reported as part of floral bouquet, and the accumulation of lipid reserves in the pre-anthesis stage and their consumption in post-anthesis indicate that the appendices are osmophores with defined morphological identity. These results confirm that the appendices present in the Schwenckieae tribe have an osmogenic function and must be involved in the mechanism of attracting pollinators.