FREUDENSTEIN, JOHN V.*, DIANA M. SENYO, AND MARK W. CHASE. Department of Evolution, Ecology and Organismal Biology, The Ohio State University, Columbus, OH 43212; Department of Biological Sciences, Kent State University, Kent, OH 44242; Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3DS. - Phylogenetic implications and comparative utility of 26S and ITS2 sequences in Orchidaceae.
As the nuclear portion of a multigene analysis of relationships in
Orchidaceae, ITS2 and the first 1200 bp of the 26S locus were
sequenced in over 60 genera from the family. Alignment of the 26S
segment was straightforward, while that of ITS2 was less so. Regions
within ITS2 varied with respect to base substitution and indel rate,
presumably reflecting secondary structure relationships in the
molecule. Equally weighted parsimony analysis of these data yielded
two most parsimonious trees, the consensus of which is well resolved.
While analysis of the 26S sequences alone gave a moderately resolved
tree, addition of the ITS2 data increased resolution and branch
support, particularly among closely related groups. Five
subfamily-level assemblages are resolved, corresponding to
Vanilloideae, Cypripedioideae, Orchidoideae (including
Spiranthoideae), and Epidendroideae. Tribal level groups are
apparent, and jackknife analysis indicates that while most of these
groups are well supported, the relationships among them often are not.
This is particularly true among groups within Epidendroideae, where
branch lengths are typically short. This is the same pattern seen in
other molecular and morphological data sets and is interpreted to
reflect a rapid radiation of epidendroid groups. Basal clades in
Epidendroideae include Neottieae, Elleanthus, Triphora
and Tropidia, with more derived groups including an Asian clade
corresponding to Podochileae, as well as a monophyletic Maxillarieae.
The patterns are highly congruent with those obtained from plastid and
mitochondrial sequence data.
Key words: 26S, ITS, Orchidaceae, phylogeny