The external morphology of the midrib of the leaf lamina is used as a diagnostic character for the taxonomy of species of Anthurium subsection Flavescentiviridia (section Urospadix) (Araceae). Our aims in this study are: characterize using morphological analysis the variation of the outline of the midrib along the leaf lamina using 22 of the 35 species of the subsection; evaluate the potential of this variation as a diagnostic tool for taxonomy. For each species, the leaf lamina was divided into three pieces of identical length. The median point of each region was transversely sectioned and its outline drawn with the aid of a camera lucida and microscope. Five distinct types of outlines were classifi ed using current terminology. Considering the diffi culty of diagnosing many of the species, this character could be useful for the taxonomy of this subsection.