Phylogenetic relationships and infraspecific variation in Canadian Arctic Poa based on chloroplast DNA restriction site data

Infraspecific variation and phylogenetic relationships of Canadian Arctic species of the genus Poa were stud- ied based on chloroplast DNA (cpDNA) variation. Restriction site analysis of polymerase chain reaction amplified cpDNA was used to reexamine the status of infraspecific taxa, reconstruct phylogenetic relationships, and reexamine previous classification systems and hypotheses of relationships. Infraspecific variation was detected in three species, but only in Poa hartzii Gand. did it correspond to infraspecific taxa where recognition of subspecies ammophila at the spe- cies level is supported. Additional variation in P. hartzii ssp. hartzii is hypothesized to be the result of hybridization with Poa glauca in the High Arctic and subsequent introgression resulting in repeated transfer of P. glauca DNA. The variation in Poa pratensis L. had a geographical rather than taxonomic basis, and is hypothesized to correspond to in- digenous arctic versus introduced extra-arctic populations. In P. glauca Vahl cpDNA variation was detected only in western Low Arctic and boreal populations and may represent greater variation where the species survived the Pleisto- cene glaciations. Cladistic parsimony analysis of cpDNA restriction site data mostly confirms recent infrageneric classi - fication systems. Poa alpina L., along with the non-arctic Poa annua L. and Poa sect. Sylvestres, formed the basalmost clades. The remaining taxa group into two main clades: one consisting of Poa sects. Poa, Homalopoa, Madropoa and Diocopoa; the second, of Poa sects. Secundae, Pandemos, Abbreviatae and Stenopoa. Poa sect. Poa, comprising Poa arctica R. Br. and P. pratensis, is a strongly supported monophyletic group, not closely related to P. alpina. Poa hartzii is confirmed as a member of a paraphyletic or weakly supported P. sect. Secundae. Poa glauca and Poa abbreviata R. Br. are distinct members within a generally unresolved Poa. sect. Stenopoa-Abbreviatae complex