Morphometric analysis and the distinction between Tibouchina hatschbachii and T. marumbiensis: morphological differentiation driven from the past

Abstract

The taxonomic delimitation of Tibouchina hatschbachii and T. marumbiensis has been subject to some controversy. According to the original descriptions, plants from grasslands on sandstone areas were identified as T. hatschbachii, whereas plants from grasslands on granite as T. marumbiensis. Due to a considerable morphological overlap, T. marumbiensis has been recognized as a synonym of T. hatschbachii, which has yet to be quantitatively investigated in natural populations. Genetic studies have shown that recent geological movements in the Ribeira do Iguape valley (RIV) region have influenced these species distributions. These events generated two geographically structured genetic lineages, apparently separated by pre- and post-zygotic reproductive barriers, which may be reflected in the morphological variation found in them. In order to investigate these morphological patterns, twenty-two morphological characters were measured for 148 specimens from nine localities and evaluated using multivariate analyses. Our results do not support the synonymization of T. marumbiensis under T. hatschbachii. Two morphological groups structured by RIV were consistent in all analyses. Group I contains all populations on sandstone plus two populations on granite, all to the west of RIV; group II comprises two populations on granite, both to the east of RIV. We therefore suggest a new circumscription for T. hatschbachii and T. marumbiensis. In this case, T. hatschbachii would be represented by the populations to the west of RIV and recognized by the smaller floral and vegetative structures, whereas T. marumbiensis would be represented by the populations to the east of RIV, with larger floral and vegetative structures.