Filogenia molecular das espécies rupícolas de Acianthera Scheidw. (Orchidaceae) e variabilidade genética do complexo Acianthera prolifera Lindl.

Abstract

The use of multidisciplinary protocols has been important to understand the evolutionary factors involved in speciation/divergence events of plant lineages. Adaptive convergence/radiation, reproductive isolation and hybridization are related to speciation, being important in lineages that are still in divergence process. The evaluation of convergence/radiation episodes, in a phylogenetic context, has proved important for the understanding of the factors acting on floral diversification and, therefore, speciation. Besides, the biogeographic events that shaped the present distribution of species are rarely considered in studies of this nature, leaving a gap on the knowledge of the influence of these events over the observed floral evolution patterns. This approach was adopted in this study, using phylogenetic, biogeography and genetic variability data, in order to: 1) test the monophyly of rupicolous species of Acianthera, a Neotropical orchid genus, occurring in eastern Brazil, with most species occurring as epiphytes in the Atlantic Rain Forest; 2) investigate the evolutionary and biogeographic factors that shaped the present distribution of Acianthera species occurring in the Brazilian campos rupestres; and 3) delimitate the entities that constitute the Acianthera prolifera complex in eastern Brazil. The rupicolous species of Acianthera were recovered in three different clades, indicating that independent occupation of the rocky outcrops occurred at least three times. These clades correspond to A. teres (four species), A. ochreata (one species and one subspecies) and A. prolifera (five species) complexes, that can only be distinguished by vegetative morphological characters. The first two include plants with ramicaul shorter than leaves, which are cylindrical or slightly conduplicated and very fleshy, being different from the plants of A. prolifera complex, which have ramicaul flattened at apex, as long as or longer than leaves, which can be conduplicated or flat, fleshy, erect or turned to ramicaul, forming a hook. According to these complexes and their sister species current distribution, it is possible to suppose that A. ochreta complex probably reached the campos rupestres from the north portion of the Atlantic Rain Forest, in Northeastern Brazil. On the other hand, the species of A. prolifera and A. teres complexes may have occupied the rocky environments reaching from eastern Brazil, and having inselbergs located at this region as the source populations. The occurrence of floral convergence between taxa of distinct complexes and divergence between taxa of the same complex, probably due to pollinators pressure, suggests that floral morphology, as opposite to vegetative, is not a good indicator of phylogenetic relationships for this group. ISSR markers enabled the recognition of A. hamosa and A. modestissima as distinct entities. However, it was not possible to differentiate genetically A. limae from A. prolifera, which configure a morphological continuum. Thus, it is suggested that these taxa, as well as some morphotypes similar to them, be considered an ochlospecies, along with A. fornograndensis, and eventually also including Andean populations frequently identified as A. prolifera sensu lato.