COMPARATIVE LEAF ANATOMY AND SYSTEMATICS IN DENDROBIUM, SECTIONS APORUM AND RHIZOBIUM (ORCHIDACEAE)

The specialized leaf anatomy for species of Dendrobium within section Aporum is similar to that of species in section Rhizobium. In both sec tions leaves are characterized by a unifacial or nearly unifacial surf ace where the exposed surface is abaxial. However, leaves in section R hizobium also feature a lacuna submerged in the mesophyll and surround ed by an adaxial epidermis. In contrast, leaves in section Aporum mere ly present an internal suture that divides the leaf into bilateral hal ves. These two sections of Dendrobium are hypothesized to be sister ta xa because of synapomorphies in their foliar anatomy. A cladistic anal ysis performed with various anatomical characters of the leaf demonstr ates that both groups are monophyletic. Little resolution was found wi thin the anatomically and morphologically distinctive Aporum clade.