PHYLOGENETICS OF THE SLIPPER ORCHIDS (CYPRIPEDIOIDEAE, ORCHIDACEAE) -NUCLEAR RDNA ITS SEQUENCES

Cypripedioideae (Orchidaceae) have been the subject of numerous taxono mic treatments with conflicting interpretations of relationships among the five genera and the 150-170 species. We have produced nuclear rib osomal ITS nucleotide sequences for nearly 100 slipper orchid species and used parsimony analysis to investigate their relationships. Our re sults demonstrate that each genus, as currently circumscribed, is mono phyletic (Mexipedium and Selenipedium being represented by a single ta xon). Like rbcL data, ITS sequences place Mexipedium sister to Phragmi pedium. Relationships at the sectional level in Paphiopedilum are larg ely as described by CRIBB. However, the division of Paphiopedilum into subgg. Brachypetalum and Paphiopedilum is not supported; subg. Brachy petalum is paraphyletic to subg. Paphiopedilum. Phragmipedium species are divided into the same three major clades as in the taxonomic schem e of McCooK. The plicate-leaved genera, Cypripedium and Sebenipedium, are successive sister groups to the rest of the subfamily, confirming generally held opinions that they display plesiomorphic characters com pared to the conduplicate-leaved genera. A survey of karyotypes in the context of the ITS tree reveals a general trend toward increased chro mosome number, probably brought about by centric fission. These data a lso accord with a previously suggested biogeographic hypothesis of a w idespread Northern Hemisphere distribution, followed by range fragment ation due to Miocene cooling.