Threadleaf Pondweed

Three distinct subspecies seemingly apparently occur in North America. They are separated mainly by the size of the plants and the peduncle characteristics. Stuckenia filiformis subsp. occidentalis typically grows in cold deep water, standing or with a strong current. This variety tends to become robust and is easily confused with Stuckenia vaginata and S. striata. Stuckenia filiformis subsp. alpina is a much smaller plant typically growing in standing waters. Stuckenia filiformis subsp. filiformis is restricted to the far north. In the intermountain region of western United States is a more robust form that is quite similar to S. filiformis subsp. alpina but although it has previously been recognized as Potamogeton [Stuckenia] filiformis var. macounii Morong (J. L. Reveal 1977b).

Stems freely branching proximally, sparsely branching distally, subterete, (10--)20--60(--100) cm. Leaves: length and width of those on main stem only slightly larger than those on branches; stipules with stipular sheaths often inflated on proximal portion of stem, 1--4(--9.5) cm, summit of midstem stipules tight to stem, ca. ± same width as stem, ligule 2--20 mm, distinct, especially on distal stipules; blade filiform or slenderly linear, 1--15 cm ´ 0.2--2(--3.7) mm, apex notched, blunt, or short-apiculate; veins 1--3. Inflorescences: peduncles terminal, erect, filiform to slender, 2--10(--15) cm; spikes cylindric to moniliform, 5--55 mm; verticels 2--6(--9). Fruits dark brown, obovoid, 2--3 ´ 1.5--2.4 mm; beak inconspicuous.

Potamogeton filiformis Persoon, Syn. Pl. 1: 152. 1805

Potamogeton filiformis Pers. Syn. PL 1 : 152. 1805
Potamogeton martnus L-. Sp. PI. 127, in part. 1753.
Potamogeton marinus Macounii Morong ; Macoun, Cat. Can. PI. 4 : 88. 1888.
Stem slender, much branched, scarcely 5 dm. long; leaves all submerged, capillary, the apex more or less pungent, 5-20 cm. long, 0.2-0.4 mm. wide, mostly 1-nerved ; stipules adnate to the leaf -bases, the sheath scarcely 5 mm. long, the free part scar ious-mar gin ed and much longer ; spikes slender, often much interrupted ; peduncles very slender, 7-20 cm. long; nutlets scarcely 1.7 mm. long, smooth, mostly without keels, the style almost invisible; embryo a complete spiral, the curved apex pointing inside the base.
Type locality : Europe.
Distribution : Quebec to the Northwest Territory, south to New York and Montana.

Potamogeton interior Rydb. Fl. Colo. 13. 1906
Potamogeton marinus occidentalis Robb. in S. Wats. Bot. King's Kxpl. 339. 1871. Potamogeton filiformis occidentalis A. Benn. Ann. Conserv. Jard. Geneve 9: 102. 1905.
Stem slender, much branched and longer than in the preceding ; leaves all submerged, capillary or narrowly linear, with an acute or more or less pungent apex, 5-15 cm. long, 0.3-1 mm. wide, mostly 1-nerved ; stipules adnate to the leaf -bases, the sheath at least 1 cm. long, the free part shorter • spikes few-flowered, often interrupted, 1-3.5 cm. long ; peduncles as thick as the stem, 3-18 cm. long ; nutlets sometimes slightly pitted, without keels or inconspicuously 1-keeled ; style almost invisible ; embryo an incomplete spiral, the straight apex pointing directly towards the base.
Type locality : Rubv Lake, Nevada.
Distribution : Ontario to the Northwest Territory, south to Utah and Colorado.

Stuckenia filiformis is a species of flowering plant belonging to the family Potamogetonaceae.

Its native range is Temperate Northern Hemisphere, Hispaniola, Ecuador to South America.

Synonym:

Potamogeton filiformis Pers.