Embriologia de Ouratea spectabilis (Mart.) Engl. e Sauvagesia racemosa A.St.-Hil. e suas implicações na sistemática de Ochnaceae

Abstract

Ochnaceae family is comprised of trees, shrubs, and rarely herbaceous plants, distributed in tropical and subtropical forests and classified as pantropical. In Brazil, the family is represented by 13 genera, with approximately 197 species. Uncertainty persists in understanding the phylogenetic relationships within these groups, raising questions and leaving gaps to be filled. In this context, studies of aspects related to embryology emerge as an investigative tool. For the study of embryology, floral buds, flowers, and fruits at different stages of development of Ouratea spectabilis (Mart.) Engl. and Sauvagesia racemosa A.St.-Hil were collected at Clube Caça e Pesca Itororó, Uberlândia, Minas Gerais. Longitudinal and transverse sections with thicknesses ranging from 4 to 6 μm were obtained using a rotary microtome These sections were subjected to staining using 0.05% toluidine blue in acetate buffer with a pH of 4.7 and were finally mounted using Entellan. The anthers of S. racemosa and O. spectabilis reveal a structure with similarities during the microsporogenesis process within the family, being tetrasporangiate and bithecate, with two middle layers, monocotyledonous wall development, apical fibrous endothecium, secretory tapetum, simultaneous cytokinesis, tetrahedral tetrads, and small bicellular pollen. The ovary presents characters observed for the subfamilies of each of the species studied in the work, O. spectabilis with apocarpous carpels and S. racemosa with fully fused syncarpous carpels, anatropous ovules, crassinucellate, linear tetrad with micropilar functional megaspore, two integuments in S. racemosa and one integument in O. spectabilis, polygonum-type embryo sac, and rapheal vascularization. In the fruit, the formation of endosperm and exotestal mechanical layer is noted. More in depth studies on the embryology of Ochnaceae and closer subclades are necessary for comparisons, as various similarities and some variations are seen within Malpighiales.