Plasticidade fenotípica em acessos de Lippia Alba (Mill.) N. E. Br. ex Britton & P. Wilson (Verbenaceae)

Abstract

Lippia alba (Verbenaceae), commonly known as erva cidreira in Brazil, is largely widespread in the Americas, where it grows in almost all environments. It is frequently grown for medicinal use. The species presents a high phenotypic plasticity, varying in habit, phyllotaxy, leaf form and size, thus putting difficulties to its taxonomical classification and use in pharmacology. Past analyses revealed the existence of different chemotypes with different pharmacological activities. The proposal of this work was understanding the great phenotypic variation observed in L. alba by making use of a multidisciplinary approach, using 32 accessions of the species collected in different Brazilian regions, and maintained in the same environmental conditions. Furthermore, another goal was characterizing the acessions and to better understand the speciation patterns ocurring in Lippia. Were found morphological variations, among the analyzed accessions, in vegetative and reproductive characters. As a result of estimating DNA quantity by means of flow cytometry, it was possible to split the accessions in seven groups with significant different quantities of DNA. Groups varied between 2.31pg and 6.70pg of DNA. In the chromosomal counting made by means of analyses in meiotic and mitotic cells, were observed six distinct chromosomal numbers (2n=30, 2n=34, 2n=51, 2n=58, 2n=60 e 2n=93), showing different ploidal levels in the species. In the pollen grains analysis were observed di, tri or tetracolporate pollen aperture. Groups with diploid accessions and smaller amounts of DNA showed only tricolporate grains. Even though the results of this study have not contributed in the division of well-defined morphological groups, they demonstrate that even under controlled conditions the accessions present morphological variations showing the existence of genetic variation as an important factor for explaining the great phenotypic plasticity observed. The existence of different ploidal levels suggests that L. alba can be in progress of speciation. Besides morphological and cytogenetic variations, those stomatal and palynological reinforces this conclusion.