Flora of the Canadian Arctic Archipelago
English: Thread-leaf pondweed,
French: Potamot filiforme.
Potamogetonaceae, Pondweed family.
Published in Type: Canada: St. Lawrence River, leg. A. Michaux. Holotype: P.
Stuckenia filiformis (Pers.) Börner subsp. alpina sensu R.R. Haynes, Les and M. Kral, non Blytt.
Synonymy. Potamogeton borealis Raf., Med. Repos. New York, ser. 2, 5: 354. 1808.
Potamogeton filiformis Pers. var. borealis (Raf.) H. St. John, Rhodora 18: 134. 1916.
Potamogeton filiformis var. macounii Morong.
Vegetative morphology. Plants (5–)10–30 cm high (or more in deep, clear, "warm" water); perennial herbs; not caespitose; sometimes vegetatively proliferating by bulbils on stems or leaves (that are white tubers borne at the ends of rhizomes). Only fibrous roots present. Ground level or underground stems horizontal; stoloniferous, or rhizomatous (if horizontal stems become buried in soft mud); elongate, or compact. Aerial stems plants aquatic without aerial stems; erect (flaccid, jointed and leafy). Leaves distributed along the stems; alternate (all submerged); dying annually and non-persistent. Stipules present (united at their base, separate at the attenuate tips; variable in form); sheathing; brown (pale), or green; glabrous. Petioles absent. Leaves grass-like. Blades 25–100(–120) mm long, 0.2–0.7 mm wide (filiform). Leaves filiform. Blades linear, veins parallel. Blade margins glabrous; apices acute.
Reproductive morphology. Flowering stems solitary; without leaves. Inflorescences spicate. Flowers per inflorescence 6–14 (in 2–4 whorls); small; radially symmetrical (actinomorphic). Sepals conventional; 4; free (one single whorl of sepal-like tepals that are valvate, and shortly clawed); green; fleshy (firm). Calyx glabrous. Petals absent. Stamens 4. Ovary superior; carpels 4 (alternating with the stamens); apocarpous. Styles absent. Ovules per ovary 1. Fruit with calyx persisting; dry; an achene; spherical (slightly flattened); black, or brown (where seed shows through the thin green fruit wall); 1.8–2 mm long; 1.6–1.8 mm wide; indehiscent. Seeds 1 (per carpel, the seed attached to the ventral margin of the carpel towards the base); 0.3–0.4 mm long; brown; surfaces smooth (or with a slight ridge and a few tubercles).
Chromosome information. 2n = 78.
2n (6x) = 78. Jørgensen et al. (1958, Greenland); Löve and Ritchie (1966b, northern Canada); Löve (1981c, northern Canada).
Ploidy levels recorded 6x.
Ecology and habitat. Substrates: aquatic; silt. Mud in shallow lakes and pools; only the inflorescence emergent.
North American distribution. Alaska, Yukon, continental Northwest Territories, Nunavut Islands, continental Nunavut, northern Quebec, Labrador. Range in the Canadian Arctic Archipelago limited. Uncommon. Low Arctic. Arctic islands: Baffin (recorded from Iqaluit), Southampton (Coral Harbour).
Northern hemisphere distribution. Amphi-Beringian, or North American. West Chukotka, East Chukotka, West Alaska, North Alaska Yukon, Central Canada, Labrador Hudson Bay, West Greenland (?), East Greenland (?, doubts about Greenland concern which subspecies).
General notes. Hultén (1968) indicated that var. borealis has a shorter, more compact spike of greater length than the leaves, low growth, and seems to be merely a growth form and apparently an adaptation to Northern conditions.
Haynes and Hellquist (2000), in the Flora of North America treatment, divided the species into three subspecies in North America - subsp. filiformis, alpina, and occidentalis - but their application outside North America is problematic. They consider the 'alpina' entity (described from Norway) as synonymous with the 'borealis' entity (described from North America), with priority for the former. Elven et al. (2005) suggested that this synonymisation may be artificial. The 'alpina' entity is considered by Russian and northwestern European botanists to be just a northern and alpine minor race or modification of the narrow-leaved 'filiformis', whereas 'borealis' seems to be a more significant broad-leaved North American entity. These authors proposed keeping 'alpina' and 'borealis' as different taxa and to synonymise the former with subsp. filiformis. The main character separating Eurasian and North American plants is leaf width, 0.2–0.4 versus 0.5–0.8 mm (Tzvelev and Elven, personal communication, 2002).
Haynes and Hellquist (2000) recorded subsp. alpina only for North America and Asia, but that is erroneous, as the name has a Norwegian typification. Blytt, who described subsp. alpina, referred to material from six sites in southern Norway (Blytt's annotated specimens are in O), and the type must be chosen among these (Tzvelev and Elven, May 2002, in discussion).
The Flora of North America treatment stated that no specimens of this taxon had been seen from Nunavut, but that it is to be expected there (Les and Haynes 1996). Vouchers specimens for the three Nunavut records on the map are housed at CAN.
Fassett (1940) considers this species to be a good duck food.
Porsild (1957) stated that plants are usually sterile in the Arctic. They are found in the muddy bottoms of shallow ponds.
The stipules of Stuckenia are adnate to the blade for two-thirds to nearly the entire length of the stipule. The few species of Potamogeton with adnate stipules have the adnation less than half the length of the stipule, or less than 4 mm. Submerged leaves of Stuckenia are opaque, channelled, and turgid, whereas those of Potamogeton are translucent, flat, and without grooves or channels (Les and Haynes 1996).
Illustrations. • Herbarium specimen. Plant less than 15 cm tall with small inflorescence and flowers or fruit close together. Nunavut, Baffin Island, Iqaluit, 1 km west of the airport terminal in a shallow pool, growing with Hippuris. D.F. Brunton and K.L. McIntosh 9901. CAN 549906. • Close-up of stipule. Midstem stipule close to and about the same width as the stem, apex indicated by upper arrow. Stipule on lower part of the stem with an inflated stipular sheath, shown by lower arrow. Nunavut, Baffin Island, Iqaluit, near airport terminal, growing with Hippuris. D.F. Brunton and K.L. McIntosh 9901. CAN 549906. • Arctic Island Distribution.
This publication is available on the internet (posted May 2011) and on CD-ROM (published in 2007). These versions are identical in content, except that the errata page for CD-ROM is accessible on the main index page of the web version.
Recommended citation for the web-based version of this publication: Aiken, S.G., Dallwitz, M.J., Consaul, L.L., McJannet, C.L., Boles, R.L., Argus, G.W., Gillett, J.M., Scott, P.J., Elven, R., LeBlanc, M.C., Gillespie, L.J., Brysting, A.K., Solstad, H., and Harris, J.G. 2007. Flora of the Canadian Arctic Archipelago: Descriptions, Illustrations, Identification, and Information Retrieval. NRC Research Press, National Research Council of Canada, Ottawa. http://nature.ca/aaflora/data, accessed on DATE.
Recommended citation for the CD-ROM version of this publication: Aiken, S.G., Dallwitz, M.J., Consaul, L.L., McJannet, C.L., Boles, R.L., Argus, G.W., Gillett, J.M., Scott, P.J., Elven, R., LeBlanc, M.C., Gillespie, L.J., Brysting, A.K., Solstad, H., and Harris, J.G. 2007. Flora of the Canadian Arctic Archipelago: Descriptions, Illustrations, Identification, and Information Retrieval. [CD-ROM] NRC Research Press, National Research Council of Canada, Ottawa..