Filogenia de Butia (Arecaceae): um gênero de palmeiras sul-americano

Abstract

Butia classification is controversial and even recent taxonomic studies are not consensual about the number of species recognized in the genus. Nor are the phylogenetic relationships among species clear. A comprehensive nomenclatural and taxonomic synopsis for Butia is needed to help to clarify the current genus systematics. A taxonomic synopsis of all names published within Butia is presented. Since the first description of species, 97 names have been published, divided between the genera Butia, Cocos and Syagrus. Subordinated to Butia, 58 names have been published (36 species, 4 subspecies and 20 varieties) of which 21 are currently recognized as accepted species (B. archeri, B. arenicola, B. campicola, B. capitata, B. catarinensis, B. eriospatha , B. exilata, B. exospadix, B. lallemantii, B. lepidotispatha, B. leptospatha, B. marmorii, B. matogrossensis, B. microspadix, B. odorata, B. paraguayensis, B. poni, B. pubispatha, B. purpurascens, B. witeckii and B. yatay). In addition, two natural hybrids between Butia and Syagrus are recognized: × Butyagrus nabonnandii (B. odorata × Syagrus romanzoffiana) and × Butyagrus alegreetensis (B. lallemantii × S. romanzoffiana). From a phylogenetic point of view, there is a constraint of DNA regions useful for palm research. Some recent phylogenetic studies have efficiently used nuclear DNA regions like ITS and WRKY and chloroplastidial like trnH-psbA. Despite Butia’s already confirmed monophyly, the phylogenetic relationships among species belonging to this genus had not yet been elucidated. In the present study, after DNA extraction, synthesys, purification and sequencing of the ITS, trnH-psbA, and WRKY19 regions, the monophyly of the genus was confirmed and Jubaea was recovered as its sister group. Despite the frequent use of chloroplast regions in the construction of phylogenies, in the present study the trnH-psbA region did not present enough phylogenetic resolution to coherently reconstruct Butia’s evolutionary history when compared to the ITS and WRKY19 core data. In general, the phylogeny obtained showed a strong geographical structure, although the Cerrado species form a paraphyletic group. On the other hand, species from southern South America form a monophyletic group from which Butia lepidotispatha, a species from the Cerrado, was recovered as the sister species of the southern clade, found in both the Atlantic Forest and Pampa regions. From the morphological point of view, it is possible to observe that the graminiform habit evolved independently several times in the genus Butia, evidencing the evolutionary convergence of this trait in non-closely related lineages. When the results are interpreted geographically, it is possible to observe that the species relationships follow a consistent geographic pattern of distribution. Similarly, it is possible to observe several shared morphological characteristics by comparing the morphology of sister species.