VEGETATIVE ANATOMY AND SYSTEMATICS OF SUBTRIBE DENDROBIINAE (ORCHIDACEAE)

Anatomy of leaf, stem, and root of more than 100 species in subtribe D endrobiinae (Orchidaceae) was studied with the light microscope to pro vide a comparative anatomical treatment of these organs, to serve as a n independent source of evidence that might be taxonomically important , and to recommend such reinterpretations of existing classifications as are suggested by a phylogenetic assessment of data. We based our cl assification on that of Rudolf Schlechter as the most complete and wid ely accepted today. We found that the anatomy of plants in subtribe De ndrobiinae reflects a high degree of morphological diversity, and many of the anatomical characters appear to be homoplasous. When these ana tomical data are used to interpret the systematic relationships among the genera, they indicate that Dendrobium is not monophyletic and that Cadetia and Pseuderia are apparently nested within the structure of D endrobium when section Grastidium is chosen as a functional outgroup. Lack of resolution in the strict consensus tree illustrates the diffic ulty of determining the phylogeneric relationships of many of Schlecht er's sections using anatomical characters. Nevertheless, we recommend that his sectional classification, with appropriate modifications base d on available data, be retained for the present, pending a more derai led understanding of the phylogeny of Dendrobiinae based on morphology , micromorphology, anatomy, and DNA studies.