Caracterização anatômica e suas implicações sistemáticas para Selaginella (Selaginellaceae)

Abstract

The species of Selaginella P. Beauv. present anatomical data used both in the characterization of species and in the subgeneric delimitations, however they are not properly explored, especially the stem and microphyll characteristics. In this context, it has been the recent circumscription of Selaginella subg. Gymnogynum that presents a weak in the definition and description of the articulation and the vascular system, where a structural revision can improve the delimitation of species in the subgenera. Therefore, the objective of this work was to describe and review the structural diversity of the articulations and the pattern of the vascular system, as well as to provide additional Information to delimit the species of S. subg. Gymnogynum. The samples were from Brazilian herbariums, representing the subgenera Gymnogynum, Exaltatae and Stachygynandrum, where they underwent the herborization reversal process and subsequent treatments were destined to light microscopy. As a result, ali species of Gymnogynum and Selaginella exaltata (subg. Exaltatae) are articulated. The region of the articulation can be characterized and classified based on the occurrence of dilatations or nodules (hyperplasia), the predominant presence of pectin in the cell wall and the formation of grooves that reach up to the cortical region (constrictions), which combine to form five articulation types, only Selaginella anaclasta (subg. Exaltatae) and Selaginella coarctata (subg Stachygynandrum) do not present articulations. The types of vascular system found were: haplostele, actinostele, plectostele and actino-plectostely. In Gymnogynum, the occurrence of bistelic haplostele was observed, besides two variations of actinostele and plectostele. The study revealed the anatomical diversity present in the stem of Selaginella subg. Gymnogynum, with additional Information for the subgenus Exaltatae and Stachygynandrum, expanding the detailed anatomical database that could contribute to a more accurate delimitation of the taxa and to later studies of evolutionary history. In the microphylls of Selaginella structures are observed that receive different denominations among them: idioblasts and papilas, and resemble the silica bodies. However, there are no studies that attest to the composition and confirm the nature of such structures. The objective of this work was to fill the gaps regarding the knowledge of siliceous bodies in the genus, based on a comparativo analysis of microphylls, with a significant sampling of five subgenera of Selaginella, to investigate the presence and distribution of silica bodies, aiming to reinterpret this character. The samples were from Brazilian herbariums, with 55 species representing the subgenus Exaltatae, Gymnogynum, Rupestrae, Selaginella and Stachygynandrum, where they underwent conventional treatments and were destined to scanning electron microscopy. In the microphyll it was found that the structures are silica bodies. Four leaf distribution patterns were observed according to the regions of the microphyll (margin, intermediate region and vein): medial-marginal; laminar; marginal; medial-costal. From the research done on mycrophylls, the creation of distribution patterns and terminological revision, certain taxonomic implications can be extracted and the presence of silica bodies is a potential synapomorphy for Selaginella. However, there is a need to deepen studies of the evolution of this character, and the in-depth anatomical analysis for the correct diagnosis is indispensable.