Panarctic Flora

240204 Stuckenia filiformis (Pers.) Börner

• Börner, Fl. Deut. Volk: 713 (1912). - Potamogeton filiformis Pers., Syn. Pl. 1: 152 (1805). Holotype (P?): Denmark: Sjælland, leg. C.F. Schumacher (see Les and Haynes 1996: 390). - Coleogeton filiformis (Pers.) Les & R.R. Haynes, Novon 6: 390 (1996).

Geography: Circumboreal-polar.

Notes: Stuckenia filiformis has been a very difficult species to handle for the Checklist. The variation is viewed differently in Eurasia and in North America. Eurasian authors do not accept races in S. filiformis except that Tzvelev (1987c) assigned the Russian Far East material to (the otherwise American) Potamogeton borealis. The northern North American material that Haynes and Hellquist revised and annotated as S. filiformis (s. lat.), in preparation for their Flora of North America treatment (Haynes and Hellquist 2000c), is extremely polymorphic (specimens in ALA and CAN studied by us). Only about half of it would readily have been assigned to this species by European or Russian investigators based on the characters emphasized by, e.g., Hylander (1953b), Tolmachev (1960), Dandy (1980), and Preston (1995). The other half would have been assigned to S. pectinata, S. subretusa, S. vaginata, or left unassigned to any of the currently accepted species. Different morphological criteria must have been applied in North America and in Eurasia, making a comparison difficult. We do not know which viewpoint is the correct one but must point to some problems.

Haynes and Hellquist divided the North American material of S. filiformis on three races: subsp. filiformis, subsp. alpina, and subsp. occidentalis. Several authors have previously considered the northern North American plant a separate race: var. borealis (e.g., Hultén 1968a; Porsild and Cody 1980; Cody 1996), based on a description from eastern Canada (Potamogeton borealis Raf.). Haynes et al. (1998), followed by Haynes and Hellquist (2000c), rather applied the name subsp. alpina for this northern plant in North America. Their subsp. filiformis and subsp. alpina are separable mainly (or only?) by the two differential characters they reported (slightly modified here): leaves 0.2-0.4 mm vs. 0.5-0.8 (1.0) mm broad, and infrutescence strongly interrupted and extended up to 4 cm vs. more compact to somewhat interrupted and extended only up to 2 cm. For their subsp. alpina, their characters must be based on American plants ('borealis') as they state they have seen no original (type) material of subsp. alpina. They reported their subsp. alpina throughout northern North America (and from Asia) and their subsp. filiformis as disjunct in south-central Alaska, the southern Yukon Territory, the Northwest Territories, and in western Greenland (and from Eurasia). Comparing North American material annotated by them as subsp. filiformis and subsp. alpina, we see little difference.

Their choice of name for this major North American race is debatable. Subspecies alpina is based on Potamogeton marinus f. alpinus Blytt (Blytt 1861) from the south-central Norwegian mountains, well outside the range they accepted for their subsp. alpina. We have inspected all the relevant syntypes (in O). In our opinion, these Norwegian plants are better interpreted as small-grown and narrow-leaved alpine modifications of S. filiformis s. str. The Norwegian name "alpina" has not been applied to anything for the last century or more. We suspect that the American choice of this name, and the disjunct range the American authors reported for their subsp. filiformis, may be a result of analysis of a mixture of southern tall-grown and northern small-grown subsp. filiformis and more broad-leaved subsp. borealis. Our contentions are that their subsp. alpina is not synonymous with var. borealis, that the name subsp. alpina may be inappropriate for North American plants, and that a name based on Rafinesque's Potamogeton borealis is the relevant one for these. We do not know where the limit between subsp. filiformis (including subsp. alpina) and subsp. borealis runs, whether in American Beringia, in the Bering Strait, or in Asian Beringia, but note that Tzvelev (1987c) considered all Asian Beringian plants as Potamogeton borealis. Neither do we know where or even whether Eurasian subsp. filiformis occurs in North America. The problem is that few morphological characters distinguish these plants, and that all yet identified characters are quantitative and plastic. A molecular study is urgently needed.

As for subsp. occidentalis, this race was originally described as a variety of Potamogeton marinus (= Stuckenia pectinata). In several features subsp. occidentalis more resembles S. pectinata and S. vaginata than it does S. filiformis: e.g., size (much larger), sheaths strongly inflated (vs. only slightly inflated), and branching more or less throughout the stem (vs. in lower parts only). Haynes and Hellquist reported subsp. occidentalis to be restricted to North America with arctic occurrences in western and northern Alaska and several places in Canada from the Mackenzie River east to Ungava. The majority of previous reports of S. pectinata and S. vaginata from northern North America may then have been transferred by these authors to subsp. occidentalis. We are reluctant to accept subsp. occidentalis (at least as annotated in the herbaria) as a race of S. filiformis. Moreover, Haynes and Hellquist assigned to their subsp. occidentalis very many specimens resembling S. pectinata and S. vaginata in several features considered diagnostic for these species by European and Russian authors.