KELCH, DEAN G.* and BRUCE G. BALDWIN. University and Jepson Herbaria, University of California, Berkeley, CA 94720. - Utility of the External Transcribed Spacer (ETS) in Compositae tribe Cardueae phylogeny reconstruction and rapid evolution of North American thistles (Cirsium species).
A 21 base-pair sequence, invariant among Carduus nutans and
Cirsium andrewsii, was used to design primer ETS-Car-1,
beginning at base pair 561 upstream from the 3’ end of ETS (referring
to the sequence of Cirsium andrewsii). A subsequent PCR of 10
diverse Cardueae taxa using primers ETS-Car-1 and 18S-E produced
products of identical length. Maximum corrected (HKY85) pairwise
ETS-region sequence divergence was 14.8% between Centaurea
calcitrapa and Atractylodes japonica. Within
Cirsium, the maximum corrected (HKY85) pairwise ETS-region
sequence divergence was found between C. henryi and C.
arvense (5.2%). For phylogenetic analysis, 52 taxa were sequenced
for ETS and ITS, including 34 North American native Cirsium
species, 13 Old World Cirsium species, and two species each of
Carduus and Onopordum. Divergence between the ITS and
ETS sequences were similar. Phylogenetic analysis supported the
monophyly of Cirsium and C. subgenus Eucirsium
(New World thistles). Two clades of West Coast species appeared; one
including Pacific Northwest and montane species with n=34 and one
comprising California endemics with n=32. ETS and ITS divergence among
Cirsium are significantly lower than in other studied groups,
as determined by comparison of divergence in six California plant
groups. The relatively low levels of rDNA spacer sequence divergence
contrast with the great ecological diversity displayed by new World
Cirsium.
Key words: Cardueae, Cirsium, Compositae, ETS, phylogeny