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loddon's pondweed, long-leaf pondweed, pondweed, potamot noeuex

Illinois pondweed, pondweed, potamot de i'Illinois, shining pondweed

Rhizomes

present.

present.

Cauline stems

terete, without spots, to 100 cm;

nodal glands absent.

terete, without spots, 28–120 cm;

nodal glands absent.

Turions

absent.

absent.

Leaves

both submersed and floating, or floating absent, ± spirally arranged.

both submersed and floating or the floating absent, ± spirally arranged.

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.

petioles continuous in color to apex, 2–9 cm;

blade adaxially light green, elliptic to oblong-elliptic, 4–19 cm × 20–65 mm, base cuneate, apex round-mucronate;

veins 13–29.

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.

sessile or petiolate, lax;

stipules persistent, conspicuous, convolute, free from blade, light brown to red-brown, not ligulate, 1–8 cm, not fibrous, not shredding at tip, apex acuminate;

petioles if present 0.5–4 cm;

blade red-brown to light green, elliptic to lanceolate or rarely linear, often arcuate, 5–20 cm × 2–45 mm, base acute, margins entire, often crispate, apex not hoodlike, acute-mucronate, lacunae in 2–5 rows each side midrib;

veins 7–19.

Inflorescences

unbranched, emersed;

peduncles not dimorphic, terminal, erect to ascending, cylindric, 3–15 cm;

spikes not dimorphic, cylindric, 20–70 mm.

emersed, unbranched;

peduncles not dimorphic, terminal or axillary, erect to ascending, cylindric, 4–30 cm;

spikes not dimorphic, cylindric, 25–70 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.

sessile, grayish green to olive green, obovoid to ovoid, laterally compressed, abaxially keeled, laterally ridged, 2.5–3.6 × 2.1–3 mm, abaxial keel well developed, lateral ridges without points;

beak erect to slightly recurved, 0.5–0.8 mm;

sides without basal tubercles;

embryo with 1 full spiral.

2n

= 52.

= 104.

Potamogeton nodosus

Potamogeton illinoensis

Phenology Flowering summer–fall. Flowering and fruiting summer–fall.
Habitat Clear to turbid waters of lakes, streams, rivers, and sloughs Alkaline waters of streams, rivers, lakes, ponds, and sloughs
Elevation 0–3300 m (0–10800 ft) 0–2700 m (0–8900 ft)
Distribution
from FNA
AL; AR; AZ; CA; CO; CT; DC; DE; FL; GA; IA; ID; IL; IN; KS; KY; LA; MA; MD; ME; MI; MN; MO; MS; MT; NC; ND; NE; NH; NJ; NM; NV; NY; OH; OK; OR; PA; RI; SC; SD; TN; TX; UT; VA; VT; WA; WI; WV; WY; AB; BC; NB; ON; QC; SK; Mexico; Central America; South America; West Indies; Eurasia
[WildflowerSearch map]
[BONAP county map]
from FNA
AL; AR; CA; CO; CT; FL; GA; IA; IL; IN; KS; KY; MA; MD; MI; MN; MO; MT; NC; NE; NH; NJ; NY; OH; OK; OR; PA; SC; SD; TX; UT; VA; VT; WA; WI; WV; WY; BC; MB; NB; NT; ON; QC; Mexico; Central America; South America; West Indies
[WildflowerSearch map]
[BONAP county map]
Discussion

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.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Potamogeton illinoensis and P. gramineus are often difficult to separate. Certainly, in the extreme of each they are easily separated, but they continually grade into each other. Features to look for are the acute-mucronate apex of the submersed leaves of P. illinoensis and the acuminate apex for P. gramineus. Also, the number of veins seems to work as well.

Three hybrids, Potamogeton illinoensis × P. nodosus (= P. × faxonii Morong), P. amplifolius × P. illinoensis (= P. × scoliophyllus Hagström), and P. gramineus × P. illinoensis [= P. × spathuliformis (J. W. Robbins) Morong], have been described.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Source FNA vol. 22. FNA vol. 22.
Parent taxa Potamogetonaceae > Potamogeton Potamogetonaceae > Potamogeton
Sibling taxa
P. alpinus, P. amplifolius, P. bicupulatus, P. clystocarpus, P. confervoides, P. crispus, P. diversifolius, P. epihydrus, P. floridanus, P. foliosus, P. friesii, P. gramineus, P. groenlandicus, P. hillii, P. illinoensis, P. natans, P. oakesianus, P. oblongus, P. obtusifolius, P. ogdenii, P. perfoliatus, P. praelongus, P. pulcher, P. pusillus, P. richardsonii, P. robbinsii, P. spirillus, P. strictifolius, P. subsibiricus, P. tennesseensis, P. vaseyi, P. zosteriformis
P. alpinus, P. amplifolius, P. bicupulatus, P. clystocarpus, P. confervoides, P. crispus, P. diversifolius, P. epihydrus, P. floridanus, P. foliosus, P. friesii, P. gramineus, P. groenlandicus, P. hillii, P. natans, P. nodosus, P. oakesianus, P. oblongus, P. obtusifolius, P. ogdenii, P. perfoliatus, P. praelongus, P. pulcher, P. pusillus, P. richardsonii, P. robbinsii, P. spirillus, P. strictifolius, P. subsibiricus, P. tennesseensis, P. vaseyi, P. zosteriformis
Name authority Poiret: in J. Lamarck et al., Encyclopedie Methodique. Botanique... Supplement 4(2): 5354. (1816) Morong: Botanical Gazette 5: 50. (1880)
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