Panarctic Flora

342603 Poa arctica R. Br.

• R. Br., Chlor. Melvill.: 30 (1823). Holotype (BM): Canada: the Northwest Territories?, "Mellville Island" the Winter Harbour area, 1819-1820, leg. J. Edwards.

2n= 42-88 (6x-ca. 12x). - Europe (N, ca. 10-12x), Russia (N, ca. 10x), Siberia (N, 8-10x), Far East (N, ca. 6-11x), Alaska (ca. 10x), Canada (ca. 9-11x). - Numerous reports.

Geography: Circumpolar-alpine.

Notes: Poa arctica s. lat. is a large and much disputed group of northern Poas. In addition to P. arctica s. str., Tzvelev (1976, PAF proposal) accepted the following species for the northernmost parts of Russia: P. almasovii, P. beringiana, P. lanata, P. lindebergii, P. malacantha, P. platyantha, and P. tolmatchewii. He treated the two proposed taxa present only in North America as subspecies of P. arctica: subsp. williamsii and subsp. longiculmis, following Hultén (1968a) who treated the variation in northwestern North America as four subspecies of P. arctica. This difference between Eurasia and North America might be due to a difference between Russian and North American botanical traditions rather than to biological differences. The variation in northern Canada, Greenland, and northwestern Europe has usually been treated as two subspecies of P. arctica (Böcher et al. 1978; Elven 1994; Elven et al. 2005), except for Scandinavia and Iceland where several local subspecies have been proposed (Nannfeldt 1940; Lid 1944 and onwards; Hylander 1953b; Löve 1970a). Edmondson (1980) did not accept any races for Europe.

Little effective exchange of opinions and no comparison of material has taken place within the PAF group concerning this aggregate. Tzvelev (in comment) stated that there is no reason to include the Russian species in a P. arctica aggregate. However, we may disagree about what an aggregate is, and in this group the North American and northwestern European viewpoints as to ranks are markedly different from Tzvelev's.

Soreng (1991, in comment) included most of the variation in North America (including Greenland) in P. arctica subsp. arctica, but he accepted an amphi-Beringian subsp. lanata, commenting (1991: 395) that: "Applying species rank to Poa lanata is unworkable. The few characters, e.g., spikelet size, coloration, and rachilla pubescence, said to distinguish P. lanata from P. arctica are not correlated or grade continuously between the taxa". At that time, he included within subsp. lanata the plants named as "williamsii", "longiculmis", and "malacantha" on the North American side, with the comment about the last-mentioned (1991: 395): "However, these variations and all combinations of them occur in my collections from Alaska and those of UBC, V, and CAN, with no evidence of underlying geographical or ecological pattern. These taxa have almost identical geographic ranges (maps, Hultén 1968a). As such, I believe P. malacantha to be synonymous with subsp. lanata". Later, Soreng et al. (2003) and Soreng (2007) relegated "longiculmis" and "williamsii" to synonyms of subsp. arctica. For our own part, we see more but less well structured variation in the Beringian regions than in non-Beringian Canada, Greenland, and northern Europe. We find it difficult to encompass this Beringian variation in only two subspecies of P. arctica but do not have a better proposal.

A lesser difference in opinion concerns the non-Beringian variation. Europeans accept an amphi-Atlantic subsp. caespitans besides the nearly circumpolar subsp. arctica. On the American side, subsp. arctica and subsp. cespitans have been considered (by, e.g., Soreng and Gillespie in comments, see below) to intergrade to a degree that prevents formal recognition of races. However, Soreng et al. (2003) provisionally accepted (their weaker "acceptance level 2") subsp. caespitans, and Soreng (2007) accepted it as one of five North American subspecies. Our (Elven, Alsos, Haugen) view concerning the plants of Greenland and northern Europe is that there are two disjunctly different groups ("arctica" and "caespitans") without signs of transition.

Some of the differences in the treatments are probably due to how one handles agamospermous and mixed sexual and agamospermous complexes. These are often treated as a series of species in the Russian tradition, with few if any comments on agamospermy. They are more often treated as polymorphic species in the North American and European traditions, where it is assumed that the formal apparatus of species classification might be impractical or inappropriate for assumedly highly reticulate, hybridogeneous, and partly agamic aggregates. Until there is a critical, experimental cross-tradition study of this group, we accept one species with three arctic subspecies, whereas the other proposed taxa are entered provisionally. However, note that we here (and in the P. pratensis group) apply the rank of subspecies for agamospermous taxa, whereas in other instances (e.g., Alchemilla and Ranunculus auricomus s. lat.) we argue against it. The reason is that we suspect that some of these groups in Poa combine agamospermy with some sexual reproduction, leading to more connections (intergrading) between the groups than in purely agamospermous ones.