Tendências evolutivas do androceu e da corola em Lavoisiereae DC. (Melastomataceae)

Abstract

Melastomataceae present remarkable morphological variation in their floral structure, which is often used to characterize tribes, genera, and/or species. Lavoisiereae DC. is one of the most diverse tribes of Melastomataceae with about 300 species distributed in the neotropical region, from southern Mexico to southern Brazil and Paraguay, with significant diversity in the rocky fields of the states of Bahia, Goiás and Minas Gerais. In this context, the present work investigated the morphology of the androecium and the coloration of the corolla of Lavoisierae, in order to identify and describe floral morphological patterns, to see if there is any tendency in the grouping of certain character states in the genera of the tribe, especially in relation to the species of Microlicia, which stand out for their expressive morphological variation in flowers. The evolutionary history of four floral morphological characters (androecium morphism, anther coloration and number of sporangia, and corolla coloration) of 120 Lavoisiereae species was estimated based on reconstruction analyses of ancestral morphological characters. Furthermore, the floral morphological data of the androecium and corolla coloration of 283 Microlicia species were quantified and associated with geographic distribution data. Our results indicate that the most recent common ancestor (MRCA) of the tribe Lavoisiereae probably had a dimorphic androecium, with concolored and tetrasporangiate anthers and flowers with a magenta corolla. However, there are some species with both isomorphic and subisomorphic androecium. The transition to the derived condition of bicolored anthers occurred exclusively in Microlicia. Twelve independent transitions have been identified throughout the evolutionary history of the tribe. Approximately 50% of Microlicia species have bicolored anthers. Twelve independent transition events from tetrasporangiate to polysporangiate anthers were observed only in Microlicia. In Lavoisiereae, polysporangiate anthers occur exclusively in Microlicia (83 spp.), corresponding to approximately 29% of its species. The magenta corolla, including light pink, pink, dark pink, and purple tones, predominates in species of Microlicia and Rhynchanthera. The white corolla occurs in a few species of Poteranthera (1 sp.) and Microlicia (19 spp.), appearing independently several times in both genera. The yellow corolla is restricted to the genus Microlicia (30 spp.), and Microlicia rubra is the only species with a red corolla. In Minas Gerais, predominate species of Microlicia with dimorphic androecium, bicolored and tetrasporangiate anthers, and flowers with magenta corolla (99 spp.), while in Bahia, there is a greater number of species with dimorphic androecium, with isomorphic androecium species standing out, representing almost all species in the genus with this characteristic (10 spp.). Furthermore, in Bahia, there is a predominance of species with concolorous anthers (61 spp.) and polysporangiate anthers (56 spp.). In Goiás, most species have a magenta corolla, dimorphic androecium, bicolored and tetrasporangiate anthers (12 spp.). The dimorphism is present in most species of Lavoisiereae and was established early in the first lineages of the tribe. Microlicia is possibly the largest known angiosperm lineage with polysporangiate anthers. Although they are not exclusive to Microlicia, the polysporangiate anthers are rare among angiosperms and in Melastomataceae.