Embriologia de Dasyphyllum vagans (Gardner) Cabrera e suas implicações na sistemática de Barnadesioideae (Asteraceae)

Abstract

Embryological studies provide information that can assist in understanding the evolution of taxonomic groups and resolve uncertain phylogenetic relationships. Asteraceae is one of the largest families of angiosperms, divided into 16 subfamilies, with Barnadesioideae being the most basal and the sister group to the rest of the family. The genus Dasyphyllum is the most representative, and Dasyphyllum vagans (Gardner) Cabrera still has its embryology unknown. In Asteraceae, there are few embryological studies on the basal lineages, which are fundamental in establishing the plesiomorphic character states and discussing the evolutionary trends of the family. This study described the development of the anther, ovary, ovule, fruit, and seed of Dasyphyllum vagans and compared them with the embryological characteristics of Calyceraceae and Goodeniaceae, families closely related to Asteraceae, as well as other basal lineages of the family. The plant material was collected at the Universidade de São Paulo in Ribeirão Preto. Part of the material was incorporated into the Herbário da Universidade de São Paulo, and the other part was dehydrated in alcohol, embedded in synthetic resin, sectioned in a rotary microtome, stained with toluidine blue, mounted in a synthetic mounting medium, and analyzed under a light microscope. The flowers exhibited five tetrasporangiate anthers, with dicotyledonous-type wall development, persistent epidermis, fibrous endothecium, ephemeral middle layer, secretory tapetum, formation of tetrahedral microspores tetrad by simultaneous cytokinesis, tricellular pollen at dispersal, and anthers with latrorse dehiscence. The ovary is inferior, bicarpellate, unilocular with a single ovule of basal placentation, presenting barnadesioid trichomes and fundamental tissue divided into two regions, differentiated by the presence of conspicuous intercellular spaces in the inner region. The ovule is anatropous, unitegmic, tenuinucellate, with funicular obturator and differentiated endothelium, and a Polygonum-type megagametophyte. The mature fruit is a cypsela, with the endocarp and inner mesocarp consumed, the outer mesocarp partially consumed, and a vascularized and lignified pappus. The seed is exotestal with cellular endosperm. The results revealed characteristics similar to those found in Calyceraceae and some basal lineages of Asteraceae, which can be considered plesiomorphic for the family, except for the tricellular pollen at dispersal and the basal ovule placentation, which is consistent only in Asteraceae. The ovary characteristics were similar to those of other Asteraceae, except for the barnadesioid trichomes, which are exclusive to Barnadesioideae. The cypsela-type fruit is a synapomorphy of Asteraceae and Calyceraceae.