GILLESPIE, LYNN J.1 and ROBERT J. SORENG2.* 1Research Division, Canadian Museum of Nature, PO Box 3443 Station D, Ottawa ON K1P 6P4; 2Botany Department. Smithsonian Institution, Washington DC 20560. - A phylogenetic analysis of Poa (Poaceae) based on cpDNA restriction site data: DNA variation versus morphological divergence.
Poa (at ca. 500 species perhaps the largest grass genus) occurs
throughout temperate and boreal regions of the globe. A new
phylogenetic study of Poa, based on data from restriction site
analysis of PCR amplified regions of chloroplast DNA (cpDNA)
(trnT-trnF, trnF-trnV, trnV-rbcL, rbcL-ORF106, trnH-trnK), expands
sampling to where about 1/6 of the species have been characterized for
cpDNA types. A broad phylogenetic structure detected in an earlier
study (Soreng, AJB 77: 1383-1400. 1990) gained additional and robust
support. Accounting for wide extrageneric sampling, Poa still remains
monophyletic if Austrofestuca is included within it. The new analysis
suggests that divergence in morphology and ecology is often decoupled
from the frequency of fixation of phylogenetically informative cpDNA
variation. Some species groups are widely distributed with strikingly
disparate morphology and ecology, yet have diverged little in their
cpDNA profiles, whereas the opposite pattern occurs in other groups.
One of the largest and most derived clades with morphologically and
ecologically diverse species that show little cpDNA divergence
includes: Austrofestuca, several P. subg. Poa sections (Dasypoa,
Dioicopoa, Homalopoa, Madropoa) and other informal groups, with
species endemic to Europe, China, Australia, North America, and South
America. One small, early diverging cpDNA lineage includes two
morphologically and ecologically unrelated subgroups (Poa subg.
Arctopoa of alkaline seeps of the high Tibetan Plateau to sub-arctic
salt marshes; and P. subg. Poa sect. Sylvestres of forests of the
Appalachian Mts.), but few cpDNA characters distinguish them. In
contrast, in another large, derived clade (P. sects. Abbreviatae,
Oreinos, Pandemos, Secundae, and Stenopoa) cpDNA variation is
extensive and phylogenetically informative variation has been detected
even within species. Morphological and ecological divergence, however,
is not as great as in the previous two clades.
Key words: Austrofestuca, chloroplast DNA, Poa, restriction site analysis