Morphology and Anatomy Support a Reclassification of the African Succulent Taxa of Senecio S.L. (Asteraceae: Senecioneae)

Abstract: Morphological and anatomical plant traits provide important characters for plant identification, and provide vital information to support classification systems based on molecular phylogenetic studies. The tribe Senecioneae (Asteraceae: Asteroideae) has recently been reclassified as a result of molecular phylogenetic investigations, and species with succulent leaves have been identified in several different clades of the tribe. We study the leaf morphology and anatomy of 20 selected species of Senecio s.l., embracing representatives of all distinct groups of leaf succulents in Senecioneae, and contrast the results with a molecular phylogeny derived from ITS sequence data. The leaves of the studied species vary as to their gross appearance (flat to terete, horizontally or seemingly vertically oriented, with or without ‘window’ areas) as well as with respect to their macro-anatomy (tissue succulence vs. all-cell succulence). The morphological and anatomical characterizations of identified groups correlate well with the clades found in the ITS-based molecular phylogenetic studies, and the reclassification of succulent-leaved species of Senecio s.l. into the segregate genera Caputia, Kleinia and Curio is strongly supported. Leaf characters provide easy-to-observe diagnostic characters to recognize the three genera.