A contribution of leaf anatomy to the taxonomy of Varronia P. Browne (Cordiaceae, Boraginales)

Abstract

Varronia (Cordiaceae, Boraginales) is a Neotropical genus of approximately 125 species. In Brazil, it is represented by 36 species, of which 21 are endemic. Regarding the vegetative organs, their species are morphologically similar, and despite recent revision studies on the genus, the identification and delimitation of some species are still problematic. In this perspective, we here investigate the leaf anatomy of ten species of Varronia recorded in Brazil, to detect diagnostic taxonomic characters and putative synapomorphies for the genus. The types and distribution of secretory and non-secretory trichomes were identified as one of the most relevant characters in differentiating the studied species. Three types of non-secretory and one type of secretory trichomes are reported in the genus for the first time. The occurrence of crystalline sand in the mesophyll was identified as a putative synapomorphy for the genus, as well as the occurrence of globular and elongated glandular trichomes, isobilateral mesophyll, hypostomatic leaves, and the occurrence of cystoliths.