GILLESPIE, LYNN J.1*, SAOOD OMER1, 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. - Chloroplast DNA restriction site variation in North American Poa section Poa.
Poa sect. Poa comprises three species and numerous
infraspecific taxa in North America. Poa pratensis and
P. arctica are widespread and morphologically highly
polymorphic with numerous infraspecific taxa, while P.
macrocalyx is restricted to coastal Alaska in North America. We
used restriction site analysis of PCR amplified chloroplast DNA
(cpDNA) to examine variation both among species and at the
infraspecific level in P. pratensis and P.
arctica. Based on our larger phylogenetic analysis of
Poa the section was determined to be a strongly supported
monophyletic group. Variation within the section was detected in only
one of the five cpDNA regions examined (trnT-trnF, trnF-trnV,
trnV-rbcL, rbcL-ORF106, trnH-trnK). All infraspecific taxa of
P. arctica examined shared an identical restriction site
haplotype, differing from the other two species in two or three
restriction sites in the rbcL-ORF106 region. In contrast, P.
pratensis exhibited infraspecific cpDNA variation in the same
region, with two cpDNA groups: an indigenous arctic/alpine complex
comprising P. pratensis subspp. alpigena and
colpodea, and an introduced non-arctic/alpine complex. These
two cpDNA groups differ in three restriction sites, a level of
variation greater than is generally found within species complexes in
Poa. They also differ considerably in length of the rbcL-ORF106
region, suggesting that these restriction site differences may be the
result of an insertion-deletion event, specifically a deletion in
arctic/alpine P. pratensis. While most P.
pratensis subsp. pratensis had the non-arctic/alpine
haplotype, Low Arctic plants were found to have the arctic/alpine
haplotype and are intermediate in overall morphology, suggesting they
may be the result of hybridization between subspecies. Poa
macrocalyx was found to share an identical haplotype with
arctic/alpine P. pratensis. We hypothesize that the two
cpDNA groups in the P. pratensis/P.
macrocalyx complex represent a fundamental division between an
indigenous (sub)arctic/alpine complex and an introduced
Key words: chloroplast DNA, P. arctica, P. pratensis, P. sect. Poa, Poa, restriction site analysis