Taxonomic implications of the leaf anatomy of twelve species of Senna ser. Bacillares (Leguminosae) from northeastern Brazil

Abstract

The leaf anatomy of twelve species of Senna ser. Bacillares (Leguminosae) from northeastern Brazil was examined to provide taxonomic support for the group. Forty-three specimens were analyzed using light microscopy, following the usual techniques in plant anatomy. Four different petiole profiles were observed: circular, semicircular, hexagonal, and pentagonal; most petioles showed adaxial projections, those being strongly prominent in S. chrysocarpa and S. quinquangulata. Six different leaf rachis profiles were observed: pentagonal, elliptic, obovate, circular, semicircular, and irregularly triangular. The vascular systems of the petioles and leaf rachisies showed similar patterns, forming 4-7 central bundles and two accessory bundles. The midrib was plane-convex in all species, with an arched vascular bundle surrounded by sclerenchyma. The dorsiventral mesophyll has a uniseriate palisade, with 4-7-seriate spongy parenchyma. Five different leaflet edge outlines were observed: rounded, recurved, acute, acuminate, and truncate; the truncate type was exclusive to S. angulate, while S. gardneriwas acuminate. Idioblasts of druses and prismatic crystals were observed in the petioles, leaf rachises, and midribs of all species; crystalline sand was observed in the petioles and leaf rachises of S. angulata and S. pluribracteata, in the petiole of S. gardneri, and in the rachis of S. splendida. The sets of different anatomical characters of the petioles, leaf rachises, and leaflet edges of all of the species studied provided additional support to the taxonomy of Sennaser. Bacillares and reinforced the importance of anatomical studies to the taxonomy and systematics of this group.