Winged stems in Pterospartum tridentatum

Abstract

Some members of the subtribe Genistinae show winged stems instead of leaves. Using techniques of light and scanning microscopy, the morphoanatomy and some microcharacters of the winged stem of Pterospartum. tridentatum are described and compared with those of other close taxa, also inserted in the Genistinae and with whom R tridentatum is mistaken: Chamaespartium tridentatum (L.) Gibbs, C. sagittale (L.) Gibbs and G. florida L. P. tridentatum winged stem presents a peculiar anatomy, with characteristics of a dicot stem and leaf. The central vein is organized as a secondary stem and vascular tissues are surrounded by a ring of mechanical elements. Some epidermal microcharacters, such as the predominant type of stomata and their way of insertion, are unique and are not found in the other Genistinae studied. These characters were not described in P. tridentatum and support its delimitation as a distinct and natural taxon.