An Approach to Spermacoceae Cham. & Schltdl. sensu lato from the view-point of certain floral characters

Abstract

Spermacoceae sensu lato is a tribe of the subfamily Rubioideae (Rubiaceae) that is referred in the literature with problems of generic delimitations. Recent investigations on the systematics, taxonomy and floristics of Brazilian species of Rubiaceae confirm this trend in the tribe, and suggest new phylogenetic and multidisciplinary studies on the group. In this context, the present paper aimed at the morphoanatomical analysis of the flowers of nine species of Spermacoceae, belonging to the genera Emmeorhiza, Galianthe, Mitracarpus, Richardia and Spermacoce, in order to indicate characters that have significant potential in the taxonomy and phylogeny of the tribe. Floral buds and flowers from vegetation in different environments were embedded in historesin and sectioned in a rotation microtome. Sepals exhibit glabrous or hairy epidermis and homogeneous mesophyll or they have atypical palisade parenchyma. Petals consist of hairy or glabrous epidermis and homogeneous mesophyll. Anthers are tetrasporangiate, and they possibly show dicotyledoneous anther wall formation. The ovary is inferior and probably appendicular in nature, consisting of mesophyll with parenchyma and precursor tissue of the sclerenchymatous pyrene of the fruit. Presence of compitum in the ovary and style characterizes the species as eu-syncarpous. The study revealed that floral structural characters related to the perianth, gynoecium and nectary have significant taxonomic potential within Spermacoceae sensu lato.