Micromorphology of leaflets of Senna series Bacillares (Leguminosae) and its taxonomic significance

Abstract

Senna ser. Bacillares (Benth.) H.S.Irwin & Barneby comprises approximately 50 species, 23 of which are found in Brazil. Micromorphological studies of the leaflet epidermis were performed on ten species of Senna ser. Bacillares collected in the Atlantic Forest north of the São Francisco River, in Northeastern Brazil, to identify qualitative and quantitative characters supporting their taxonomy. All species showed a uniseriate epidermis, hypostomatic leaflets, and more than one type of stomata (the paracytic type being predominant). Different types of epicuticular waxes were observed, including microplatelets as rosettes (characteristic of Fabaceae), fissured layers, and membranous platelets. A glabrous epidermis on both surfaces was characteristic of Senna splendida (Vogel) H.S.Irwin & Barneby, and disperse trichomes were observed on the abaxial surface of Senna quinquangulata (Rich.) H.S.Irwin & Barneby. Straight to curved anticlinal cell walls were observed in most species, the curved pattern was exclusive to Senna quinquangulata and sinuous types on the abaxial surfaces of Senna macranthera (DC. ex Collad.) H.S.Irwin & Barneby and Senna splendida. A papillose epidermis on the abaxial surface was common to seven species. Four types of stomata were observed, including the anomotetracytic type, which has not been previously reported in Senna Mill. Spherical crystals and crystal sand are reported here for Senna for the first time. Those sets of micromorphological characters provide additional subsidies for the taxonomy of Senna ser. Bacillares, as well as for the genus Senna.