MORGAN, DAVID R. Department of Biology, Western Washington University, Bellingham, WA 98225. - Nuclear rDNA ETS sequence data and the systematics of Machaeranthera (Asteraceae).
Previous research on the systematics of Machaeranthera and its
relatives using chloroplast DNA and ITS sequence data have left
several questions unresolved. New sequence data from the external
transcribed spacer of nuclear rDNA (ETS) were generated in an attempt
to resolve these questions. ETS sequence data were obtained from the
same taxa that were used for previous analyses with chloroplast DNA
and ITS sequences. ETS evidence provides greater resolution than does
ITS evidence, and greater support for monophyletic groups, permitting
further resolution of the relationships of Machaeranthera.
Phylogenetic analysis of these data supports relationships that differ
substantially from those supported by chloroplast DNA for several
species and groups of species. These taxa include Machaeranthera
gypsitherma, M. viscida, M. heterophylla, the
Machaeranthera section Arida, and the genus
Pyrrocoma. The relationships that the molecular data support
for these taxa suggest that their chloroplast DNA and their nuclear
rDNA have come from separate lineages, and that they may have
experienced reticulate evolution in their phylogenetic history.
Key words: Asteraceae, external transcribed spacer, Machaeranthera, nrDNA