Loddon Pondweed

Foodplant / pathogen
amphigenous colony of Mycocentrospora anamorph of Mycocentrospora acerina infects and damages live leaf of Potamogeton nodosus

Sometimes confused with Potamogeton natans L., but submerged leaves not reduced to narrowly linear phyllodes, and petioles without discoloured joints at the tips. Common from hills to the plains of our area.

Six hybrids, Potamogeton gramineus ´ P. nodosus (= P. ´ argutulus Hagström), P. illinoensis ´ P. nodosus (= P. ´ faxonii Morong), P. nodosus ´ P. richardsonii (= P. ´ rectifolius A. Bennett), P. natans ´ P. nodosus (= P. ´ schreberi Fischer [P. ´ perplexus A. Bennett]), P. alpinus ´ P. nodosus (= P. ´ subotusus Hagström), and P. epihydrus ´ P. nodosus (= P. ´ subsessilis Hagström), have been described.

Potamogeton nodosus is a common floating-leaved species throughout much of the United States and southern Canada. When both submersed and floating leaves are present, it is very easily recognized by the petioles of the submersed leaves being longer than 5 cm.

Perennial, rhizomatous, aquatic. Stem branched, leafy, terete, simple. Leaves heterophyllous, submerged leaves petiolate, lanceolate or broadly lanceolate-oblong, veins 9 or more, thin translucent, 6-10.5 cm long; floating leaves broadly ovate, elliptic, coriaceous, of firm texture, 4-16 cm long, 2-5 cm broad, entire. Stipules free, keeled, lanceolate 2-15 cm long, 8-10 mm broad. Spikes cylindric, 4.5-11 cm long, 1.5-2.5 mm broad; peduncle 7-11 cm long. Flowers in whorls, sessile, small. Perianth segments small, obtuse, entire, c. 1.5 mm long. Stigma short. Fruitlets 3-4 mm long, 2-3 mm broad, obliquely obovoid, spongy, ventral margin convex, shortly beaked.

Rhizomes present. Cauline stems terete, without spots, to 100 cm; nodal glands absent. Turions absent. Leaves both submersed and floating, or floating absent, ± spirally arranged. Submersed leaves petiolate, lax; stipules persistent to deliquescent, conspicuous, convolute, free from blade, light brown, not ligulate, 3--9 cm, not fibrous, not shredding at tip, apex round to acute; petioles 2--13 cm; blade light to dark green, linear-lanceolate to lance-elliptic, not arcuate, 9--20 cm ´ 10--35 mm, base acute, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, acute, without sharp awl-like tip, lacunae in 2--5 rows each side of midrib; veins 7--15. Floating leaves: petioles 3.5--26 cm; blade adaxially light green, lenticular to elliptic, 3--11 cm ´ 15--45 mm, base cuneate to rounded, apex acute to rounded; veins 9--21. Inflorescences unbranched, emersed; peduncles not dimorphic, terminal, erect to ascending, cylindric, 3--15 cm; spikes not dimorphic, cylindric, 20--70 mm. Fruits sessile, red to reddish brown, obovoid, abaxially keeled, laterally ridged, 2.7--4.3 ´ 2.5--3 mm, keel well developed, lateral ridges with blunt to sharp tips; beak erect; sides without basal tubercles; embryo with 1 full spiral. 2n = 52.

Warm temperate and tropical regions of Europe, Africa, Asia and America.

Distribution: Warmer regions of Europe, N. and Cent. America, Africa and Asia.

Alta., B.C., N.B., Ont., Que., Sask.; Ala., Ariz., Ark., Calif., Colo., Conn., Del., D.C., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo.; Mexico; West Indies; Central America; South America; Eurasia.

600-3000 m

Fl. Per.: April-August.

Flowering summer--fall.

Clear to turbid waters of lakes, streams, rivers, and sloughs; 0--3300m.

Herb, with stems to 1 m, arising from a woody rhizome. Stipules variable in size (up to 6 cm), open, convolute, membranous, lower amplexicaul, upper spreading, ovate, acuminate. Upper leaves floating and sometimes aerial on mud, submerged ones often soon decaying; all leaves petiolate. Submerged leaves: 8-20 × 0.8-1.6 cm, linear to linear-lanceolate, thin, tapering to apex; floating leaves: 5(-8) × 2.5(-3.5) cm, elliptic to ovate, coriaceous; apex rounded to acute; leaves intermediate between the two forms occur. Leaves of land forms usually smaller. Spikes on ± swollen, arcuate scapes, many-flowered. Drupe c.4 mm, rounded, flattened; beak short.

Widespread in Africa, Madagascar, Indian Ocean islands, Europe, Asia, and North and Central America.

Potamogeton mexicanus A. Benn. Jour. Bot. 25 : 289. 1887
Stem simple; floating leaves petioled; blades coriaceous, elliptic-lanceolate, acute at
both ends, 5.3-10 cm. long, 1.6-2.8 cm. wide, sometimes revolute; petioles as long as the
blades or longer ; stipules axillary and free from the petioles, 2.5-3.4 cm. long, acute ;
submerged leaves petioled ; blades oblong-lanceolate or elliptic, acute or acuminate at the
apex, narrowed at the acute base, 6.5-11 cm. long, 2.5-3.1 cm. wide ; petioles as long as
the blade or shorter ; spikes cylindric, few-flowered, 3-3.5 cm. long ; peduncle as thick as
the petioles or thicker, 4-6.5 cm. long ; nutlets 3-keeled, the middle keel denticulate, the
smaller lateral keels tuberculate ; embryo an incomplete spiral, the straight apex pointing
directly toward the base.
Type locality : Valle de Myrica, Mexico.
Distribution : Known only from the type locality and from San L/uis Potosi.

Potamogeton occidentalis Sieber, L,innaea 2 : 224. 1827
Poiamogeton fiuitans Roth, FL Germ. 1 : 72, in part. 1788.
Stem simple or branched; floating leaves petioled; blades coriaceous, elliptic-lanceolate, acutely attenuate at both ends, 4-10 cm. long, 1.5-2.3 cm. wide ; primary nerves mostly 5, but often with intermediary secondary ones; petioles as thick as the stem and up to 12 cm. long; submerged leaves petioled ; blades translucent, elliptic-lanceolate, 6-12 cm. long, as wide as or a little wider than the floating leaf -blades, acute at both ends, petioles 0.5-4 cm. long; stipules acute or acuminate, 1.5-4 cm. long; spikes cylindric, 1-3.5 cm. long, many-flowered, sometimes interrupted ; peduncles as thick as the petioles or thicker, 4-10 cm. long; nutlets smooth, 3-keeled, the middle keel often prominently winged on the Upper half ; embryo a complete spiral, the curved apex pointing inside the base.

Potamogeton nodosus is a species of aquatic plant known by the common names longleaf pondweed and Loddon pondweed. It is native to Eurasia and the Americas, where it is widespread and can be found in water bodies such as ponds, lakes, ditches, and streams. This is a perennial herb producing a thin, branching stem easily exceeding a meter in maximum length. The leaves are linear to widely lance-shaped and up to 15 centimeters long by 4 wide. Both floating leaves and submerged leaves are borne on long petioles, a distinguishing characteristic. The inflorescence is a spike of many small flowers arising from the water on a peduncle.