WHITTON, JEANNETTE*, STACEY THOMPSON, KATRINA DLUGOSCH, and LINDA P. JENNINGS. Dept. of Botany, The University of British Columbia, Vancouver, BC, Canada V6T 1Z4. - Phylogenetic relationships in the genus Townsendia (Asteraceae: Astereae) based on nuclear ribosomal DNA variation in ITS and ETS regions.
The North American genus Townsendia comprises approximately 25-30 taxa
that occur predominantly at mid to high elevations in the Rocky
Mountains. Most species have narrow distributions: some are restricted
to specific edaphic conditions, and species of Townsendia are assigned
conservation status in both Canada and the United States. The genus
includes annual, biennial and perennial taxa. In addition, diploid
sexual and polyploid asexual populations occur in a number of species,
and the genus has been considered a single agamic complex. We have
sequenced the nuclear ribosomal spacers ETS and ITS for
representatives of most taxa. Phylogenetic trees obtained from
separate and combined analyses are all essentially congruent and
reveal strong support for the monophyly of the genus, and the presence
of a number of well-supported groupings. The deepest divergence within
Townsendia separates the only annual species, T. annua, from the
remainder of the genus. This findings contradicts the hypothesis
proposed in Beaman’s 1957 monograph of the genus. In addition, our
analysis reveals that apomixis and polyploidy are scattered among
groups that include species known only as diploid sexuals. One
well-supported clade includes a number of taxa known to have apomixis,
but three additional groupings include both sexual and apomictic
species. Thus, the genus provides an ideal study system in which to
examine the evolution and spread of apomixis.
Key words: apomixis, Asteraceae, ETS, ITS, phylogeny, polyploidy, Townsendia