SENYO, DIANA M. AND JOHN V. FREUDENSTEIN.* Department of Biology, Kent State University, Kent, OH 44242, Dept. of Evolution, Ecology and Organismal Biology, Ohio State University, Columbus OH 43212. - A molecular phylogeny of Corallorhiza (Orchidaceae) and related genera.
Corallorhiza Gagnebin (Orchidaceae) comprises eleven species of
leafless, rootless, mycotrophic orchids. Closely related genera
(Aplectrum, Cremastra, and Oreorchis) all possess
leaves and roots. Because morphological synapomorphies for
Corallorhiza are all loss characters, additional evidence for
its monophyly was sought with molecular characters; these data were
also used to study relationships among the species of
Corallorhiza and among genera of the Corallorhizinae. The ITS
region of nuclear ribosomal DNA and the chloroplast gene matK
were sequenced for multiple accessions of Corallorhiza
(representing 8 of 11 spp.), Aplectrum (1 of 1 sp.),
Cremastra (2 of 2 spp.), and Oreorchis (1 of 16 spp.).
Govenia and Coelia were used as outgroups in the
parsimony analysis. ITS data suggest that the relationships among the
genera are Aplectrum (Cremastra (Oreorchis,
Corallorhiza)), while matK differs in the positions of
Aplectrum and Cremastra. Molecular data also support
the monophyly of Corallorhiza. Relationships among the species
are congruent with previous phylogenetic hypotheses based on plastid
RFLP patterns. Corallorhiza bentleyi, a newly described West
Virginian species, is sister to a small-flowered accession of C.
striata from southern Mexico. Since previous analyses provided
evidence of deletions in the plastid genome in Corallorhiza, we
investigated this more finely by amplifying a segment of the
chloroplast genome that includes the gene psbA in
Corallorhiza and outgroups. The size of this segment is ca.
2150 bp in Govenia, 2050 bp in Aplectrum, 2250-2350 bp
in Cremastra, and 2000 bp in Oreorchis. Within
Corallorhiza it appears that both insertions and deletions have
occurred, with sizes ranging from 2300 bp among larger flowered C.
striata to 1750 bp in C. bentleyi and its sister C.
striata accession. Other species exhibit less pronounced
variation, but multiple accessions of a species often exhibit the same
Key words: Aplectrum, Corallorhiza, Cremastra, molecular phylogeny, Orchidaceae, Oreorchis