CHARACTER TRANSFORMATION AND RELATIONSHIPS IN CORALLORHIZA (ORCHIDACEAE, EPIDENDROIDEAE) .2. MORPHOLOGICAL VARIATION AND PHYLOGENETIC ANALYSIS

Morphological and anatomical study of Corallorhiza, a genus of primarily New World leafless mycoparasitic orchids, was undertaken in order to produce a hypothesis of relationships among the species and to gain some understanding of character transformations. Cladistic analysis of the resulting data set gave two most parsimonious trees. Analysis of combined plastid DNA and morphological data yielded a single topology, identical to one of the two from the analysis of morphological data alone. Molecular data do not conflict with the morphological data set, and provide more resolution within the C. maculata complex. The combined data indicate that C. striata is the sister group to the remainder of the genus; the circumboreal C. trifida also occupies a basal position. Corallorhiza wisteriana and C. odontorhiza comprise the sister group to the C. maculata + C. mertensiana + C. bulbosa clade. Only two synapomorphies, presence of the coralloid rhizome and loss of leaves, unite the species of Corallorhiza. The coralloid rhizome appears to be a paedomorphic development, due to its similarity to a protocorm; if so, it too is a loss character and may be considered only weak support for monophyly of the genus. Predominant autogamy, seen in C. trifida and cleistogamous C. odontorhiza, has probably arisen independently in these taxa.