Stuckenia filiformis
Stuckenia
fineleaf pondweed, slender-leaf pondweed, thread-leaf false pondweed, thread-leaf pondweed, western pondweed
pondweed, potamot
freely branching proximally, sparsely branching distally, subterete, (10–)20–60(–100) cm.
terete, nodes without oil glands.
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.
submersed, alternate, opaque, sessile, linear, channeled, turgid, acute at base acute, margins entire, apex obtuse to acute, veins 1–5;
stipules not tubular, adnate to base of leaf blades for 2/3 or more length of stipule, extending past adnation as free ligule.
peduncles terminal, erect, filiform to slender, 2–10(–15) cm;
spikes cylindric to moniliform, 5–55 mm;
verticels 2–6(–9).
spikes, capitate or cylindric, submersed;
peduncles flexible, not projecting inflorescence above surface of water.
pistils 4.
dark brown, obovoid, 2–3 × 1.5–2.4 mm;
beak inconspicuous.
abaxially rounded, beaked or not, turgid;
embryo with less than 1 full coil.
= 13.
Stuckenia filiformis
Stuckenia
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).
Subspecies ca. 5 (3 in the flora).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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, in fact, less than 4 mm. Submersed leaves of Potamogeton are translucent, flat, and without grooves or channels, whereas those of Stuckenia are opaque, channeled, and turgid.
A proposal to elevate Potamogeton subgenus. Coleogeton to the generic level, retaining the name Coleogeton, was presented (D. H. Les and R. R. Haynes 1996). Potamogeton pectinatus Linnaeus was chosen as the nomenclatural type. The name Stuckenia had been previously published, however, and P. pectinatus cited (C. Börner 1912), making the generic name Coleogeton superfluous. Stuckenia is the correct name, and the appropriate specific combinations have been made (J. Holub 1997).
Species ca. 6 (4 in the flora).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Plants 20–100 cm; stipules on proximal portion of stem inflated, disintegrating with age; fruits often absent. | subsp. occidentalis |
1. Plants 10–30 cm; stipules on proximal portion of stem tightly clasping or slightly enlarged, persistent; fruits common. | → 2 |
2. Peduncles Peduncles with flowers and/or fruits 4 cm or more apart; leaves 0.2–0.5 mm wide. | subsp. Filiformis |
2. Peduncles with flowers and/or fruits less than 4 cm apart; leaves to 1 mm widee. | subsp. alpina |
1. Leaf apex acute, apiculate, cuspidate, rarely round; proximal stipular sheaths not inflated; stems abundantly branched, especially on distal portions; fruits distinctly beaked. | → 2 |
1. Leaf apex notched, obtuse, or round, rarely apiculate; proximal stipular sheaths often inflated; stems sparsely branched on distal portions; fruits without beak. | → 3 |
2. Leaves 0.4–1.5–3(–8.5) mm wide; leaf apex apiculate, cuspidate, or rarely round; plants from restricted range in western United States. | S. striata |
2. Leaves 0.2–1 mm wide; leaf apex acute to mucronate or apiculate; widespread throughout United States and Canada. | S. pectinata |
3. Stipules with distinct ligules to 20 mm, especially on distal stipules; summit of midstem stipules tight to stem, about the ± same width as stem; fruit 2–3 mm. | S. filiformis |
3. Stipules without ligules or these to 2 mm on distal stipules; summit of midstem stipules inflated at least 2 times width of stem; fruit 3–3.8 mm. | S. vaginata |
BC
Go Botany
MI Flora
MN Wildflowers- Local floras:
CA, 
OR, 
WA - Local Web sites: CalFlora, CalPhotos,
Flora NW, 
PNW Herbaria 
WildflowerSearch
iNaturalist (observations)
USDA Plants Database- LBJ Wildflower Center
- SEINet
- Plants of the World Online
- Encyclopedia of Life
- Wikipedia
- Google Image Search
