Morphological variability in rupicolous species of the Acianthera prolifera complex (Orchidaceae) occurring in southeastern Brazil

We carried out multivariate morphometric analysis of 23 floral characters in seven populations of a complex of four species of Acianthera (Orchidaceae) occurring in Brazilian campo rupestre (rocky field) vegetation (A. hamosa, A. limae, A. modestissima, and A. prolifera) that flower synchronously and are partially intercompatible, and one putative hybrid population between A. limae and A. prolifera. We also carried out cluster analysis involving these eight populations plus 21 populations of a previously published study belonging to another species complex of Acianthera occurring in campo rupestre, including 12 floral characters in the analysis. Allopatric species pollinated by the same group of Diptera showed higher floral similarity among themselves than to a sympatric species pollinated by another group of Diptera. Such patterns indicate the existence of floral convergence in allopatric species and/or radiation in sympatric species. The analysis also indicated that there is more floral similarity between species of different complexes but that share the same group of pollinators. Large overlap was observed between A. limae and the putative sympatric hybrids, indicating the occurrence of later generations of hybrids and/or individuals of A. limae with introgression. The results do not support A. hamosa and A. modestissima as distinct species. These taxa are geographically isolated, occurring in different environments, are recognized only by vegetative characters that show high phenotypic plasticity, and share the same pollinators, being interfertile.