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 sections leaves are characterized by a unifacial or nearly unifacial surface where the exposed surface is abaxial. However, leaves in section Rhizobium also feature a lacuna submerged in the mesophyll and surrounded by an adaxial epidermis. In contrast, leaves in section Aporum merely present an internal suture that divides the leaf into bilateral halves. These two sections of Dendrobium are hypothesized to be sister taxa because of synapomorphies in their foliar anatomy. A cladistic analysis performed with various anatomical characters of the leaf demonstrates that both groups are monophyletic. Little resolution was found within the anatomically and morphologically distinctive Aporum clade.