Caracteres estruturais foliares e suas implicações na taxonomia de Lavoisiera, Microlicia e Trembleya (Microlicieae, Melastomataceae)

Abstract

Members of Melastomataceae are easily recognized by the leaves with acrodomous venation; bisexual, actinomorphic and diplostemonous flowers; and stamens with elongated connective or appendices. The family is well represented in Brazil, occurring in different vegetation formations from Amazônia to Rio Grande do Sul. From the 11 tribes of the family, Melastomeae, Miconieae and Microlicieae are the most representative of Brazil. The latter, in particular, is considered the largest tribe of Melastomataceae with capsular fruits, with six genera: Chaetostoma DC., Lavoisiera DC., Microlicia D.Don, Rhynchanthera DC., Stenodon Naudin and Trembleya DC. The tribe, although monophyletic, presents a polytomy between genera, thus, further studies are needed to elucidate the intergeneric relationships, especially among the related ones, as Lavoisiera, Microlicia and Trembleya, in which the reproductive features used to define them, usually overlap. More specifically in Microlicia, the diagnostic features are usually tenuous, making difficult the recognition of closely related species. Due to this context and the importance of morphological and anatomical foliar studies to the recognition of different taxa in Melastomataceae, this study defines the foliar structural features that may characterize Lavoisiera, Microlicia and Trembleya and also the Microlicieae (Chapter 1), also including the diagnostical anatomical characters in leaves of four new Microlicia species (Chapter 2). The morphological and anatomical results indicate useful characteristics to the recognition of the three studied genera, such as: sessile leaves with conspicuous isobilateral mesophyll and supporting tissue in the leaf margin of Lavoisiera; foliar depressions and homogeneous mesophyll in Microlicia; and petiolated, microphyll and hypostomatic leaves in Trembleya. Concerning to the tribe some features seem to be common, such as uniseriate epidermis with cells walls generally straight to slightly sinuous, covered with a thin cuticle; slightly elevated stomata; short stalk trichome and palisade parenchyma on both sides. Our results also indicate adaptive aspects of Microlicieae leaves, as the leaf reduction from the short or absent petioles and leaf blades of small size, and even evolutionary, as the most developed veins with bicollateral bundles shaped pronounced arch in Trembleya, which is possibly basal among Microlicieae. The characteristics and similarity between Lavoisiera and Trembleya species corroborate the fact that these two groups are more defined than Microlicia. The latter genus displays a heterogeneous morphological and anatomical pattern, organized into two major groups with distinct similarity values. This complexity in Microlicia appears to be related to leaf reduction process, and thus our results confirm its parafiletic status, as reported by other studies. Still regarding to Microlicia, several features can be used to distinguish the new species, such morphological, as the presence of petiole and depressions in foliar blade, such anatomic as the size and shape of epidermal cells, mesophyll organization, organization of veins and vascular bundles, and the distribution of phenolic substances. Thus, our study indicates characteristics that contribute to the recognition of genera and tribe studied, corroborating the importance of foliar characters in the recognition of different family groups.