Panarctic Flora

342603b Poa arctica subsp. caespitans Simmons ex Nannf.

• Nannf., Symb. Bot. Upsal. 4, 4: 71 (1940). - Poa arctica var. caespitans (Simmons ex Nannf.) Hyl., Nomenkl. Stud. Nord. Gefässpfl.: 78 (1945). Lectotype (UPS!): Canada: Nunavut, Ellesmere Island, Harbour Fjord, leg. H.G. Simmons 4000 (Nannfeldt 1940: 71).
• Poa filipes Lange, Consp. Fl. Groenland. 3: 175 (1890). - Nomen novum for Poa trichopoda Lange, Fl. Dan. 17, 49: 4, t. 2885 (1877), non Helds. & Sartori ex Boiss. (1859). Holotype (C): Greenland: Kaiser Franz-Josephs Fjord, 1869-1870, leg. Buchenau.

2n= 56 (8x). - Europe (N), Canada, Greenland. - Numerous reports.

Geography: North American (NE) - amphi-Atlantic - European (N): NOR RUS CAN GRL.

Notes: In Europe, Poa arctica subsp. caespitans is frequent in Svalbard and Novaya Zemlya but has only been found in a few places in the non-arctic parts of the northern Scandinavian mountains.

Haugen and Elven: Poa arctica subsp. caespitans is still disputed and treated differently in Russia, northwestern Europe, and North America. Tzvelev (1976: 455) synonymized subsp. caespitans with P. tolmatchewii Roshev. and stated it to be "undoubtedly hybridogeneous (or even a modern hybrid: P. arctica x glauca)". This raises two questions: whether the two names are synonymous and whether the hybrid hypothesis can be supported. In Russia, Tzvelev (PAF proposal) reported P. tolmatchewii from Taimyr, Anabar-Olenyok, and Kharaulakh in Siberia and from West Chukotka and Wrangel Island in the Russian Far East, everywhere as rare. Morphological investigations (Haugen 2000) demonstrated that subsp. caespitans as described and with type from Canada differs in the majority of the diagnostic characters reported by Tzvelev for P. tolmatchewii. The synonymization is not accepted. Material observed in the field from Kharaulakh in 2004 (Elven and Solstad), fitting Tzvelev's description of P. tolmatchewii, differs appreciably from P. arctica subsp. caespitans. Tzvelev's hybrid hypothesis may well be true for P. tolmatchewii (which therefore is excluded until it can be substantiated as a taxon independent from its presumed parents), but it is not supported for subsp. caespitans which shows no additive pattern in isoenzymes compared with the parents proposed by Tzvelev (Haugen 2000).

Nordic authors (e.g., Nannfeldt 1940; Hylander 1953b; Elven et al. 2005) have considered subsp. caespitans a major race of P. arctica. Poa arctica subsp. caespitans seems to be simpler genetically than the main body of P. arctica subsp. arctica, with fewer molecular markers (Haugen 2000: few enzyme multilocus phenotypes) and generally at a constant and lower ploidy level. It seems to be octoploid, whereas most voucher-supported counts of P. arctica subsp. arctica - at least from the amphi-Atlantic areas - are at 9x or higher. In Svalbard, subsp. arctica and subsp. caespitans co-occur without any observed transitional forms. The Svalbard plants of subsp. caespitans are pollen-sterile and agamospermous as are the Canadian plants we have investigated, including the pollen-sterile type specimens. If subsp. caespitans is a result of hybridization, it might be a fairly well stabilized and widespread agamospermous offspring from a parental taxon in the P. arctica aggregate and a more low-ploid species. Note that P. glauca, as a proposed parent, is a high-polyploid in the High Arctic (mostly 8-10x). In Nordic opinion, subsp. caespitans is an acceptable taxon (subspecies or rather species, P. filipes) and is more distinctly different from subsp. arctica than the amphi-Beringian subsp. lanata. It seems to reach across the North Atlantic from central arctic Canada in the west to Novaya Zemlya in the east. We have seen no specimens of subsp. caespitans in the material from northwestern North America (we therefore do not accept the records of Hultén 1968a from Alaska), whereas it nearly dominates in the material from northeastern Canada and much of Greenland. In Novaya Zemlya and Svalbard, subsp. arctica and subsp. caespitans co-occur in slightly different site types, subsp. caespitans more often in dry sites and screes.

The North American opinion, as expressed by Soreng and Gillespie (in comments), has been that it is not possible to consistently distinguish a tussocky subsp. caespitans apart from a rhizomatous subsp. arctica. They did not find variation in molecular markers (sequences) in Canadian P. arctica ("but have not yet looked at extremely variable regions of the genome"), unlike the isoenzymatic data in the geographically restricted Svalbard material. This implies that subsp. caespitans might be one (in Nordic opinion) or several (in North American opinion) peripheral segregates of a larger variation. However, Soreng et al. (2003) and Soreng (2007) more or less accepted subsp. caespitans.

In the Svalbard material, subsp. caespitans is recognizable at a glance and differs from subsp. arctica in several characters (e.g., usually one spikelet per branch vs. several, stiff panicle branches vs. flexuous, flat and comparatively broad leaves vs. very narrow, purplish color of sheaths and leaves vs. violet-grey, and tussocky growth with short rhizomes vs. extended growth with long rhizomes). If this plant is accepted as species, the name P. filipes Lange 1890 based on P. trichopoda Lange 1877 (a homonym) is the relevant one. Lange's illustration clearly shows a plant corresponding to our concept of subsp. caespitans. We have been very close to acceptance of P. filipes as a species besides P. arctica.