The green links below add additional plants to the comparison table. Blue links lead to other Web sites.
enable glossary links

small pondweed

broad-leaf pondweed, floating pondweed, floating-leaf pondweed, potamot flottat

Rhizomes

absent.

present.

Cauline stems

terete to slightly compressed, without spots, 18–150 cm;

glands present on at least some nodes, green, gold, brown, or rarely white, to 0.5 mm diam.

terete, often rust-spotted, 30–90 cm;

nodal glands absent.

Turions

common, soft, lateral or terminal, 0.9–3.2 cm × 0.3–1.8 mm, soft;

leaves ± 2-ranked;

outer leaves 1–3 per side, base not corrugate, apex subulate to obtuse;

inner leaves rolled into hardened fusiform structure.

absent.

Leaves

submersed, ± spirally arranged, sessile, delicate to coarse;

stipules persistent, inconspicuous, connate or convolute, free from base of blade, brown to green or white, not ligulate, 0.31–0.92 cm, rarely appearing fibrous, not shredding at tip, apex obtuse;

blade pale green to olive-green, rarely somewhat reddish, linear, not arcuate, 0.9–6.5 cm × 0.2–2.5 mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, subulate to obtuse, lacunae absent or present, in 0–5 rows each side of midrib;

veins 1–3(–5).

both submersed and floating, ± spirally arranged.

Floating leaves

petioles lighter green immediately proximal to apex, 5.5–29 cm;

blade adaxially light green, elliptic to ovate, 3.5–11 cm × 15–60 mm, base cordate, apex acute to rounded;

veins 17–37.

Submersed leaves

sessile, rigid;

stipules persistent, conspicuous, convolute, free from blade, whitish, not ligulate, 4.5–1 cm, fibrous, not shredding at tip, apex obtuse;

blade light to dark green, phyllodial, not arcuate, 9–20 cm × 0.7–2.5 mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, obtuse, lacunae absent;

veins 3–5, obscure.

Inflorescences

unbranched, submersed or emersed;

peduncles not dimorphic, axillary or terminal, erect, rarely recurved, filiform to slightly clavate, 0.5–6.2(–6.6) cm;

spikes not dimorphic, capitate to cylindric, 1.5–10.1 mm.

unbranched, emersed;

peduncles not dimorphic, terminal, erect to ascending, cylindric, 4.5–9.5 cm;

spikes not dimorphic, cylindric, 25–50 mm.

Fruits

sessile, green to brown, ovoid to obovoid, turgid to concave, not abaxially or laterally keeled, 1.5–2.2 × 1.2–1.6 mm;

beak erect, 0.1–0.6;

sides without basal tubercles;

embryo with less than 1 full spiral.

sessile, green to greenish brown, obovoid, turgid, not abaxially or laterally keeled, 3.5–5 × 2–3 mm;

beak erect to apically recurved, 0.4–0.8 mm;

sides without basal tubercles;

embryo with 1 full spiral.

2n

= 52.

Potamogeton pusillus

Potamogeton natans

Phenology Flowering summer–fall.
Habitat Quiet or slow-flowing waters of ponds, lakes, and streams
Elevation 0–3100 m [0–10200 ft]
Distribution
from FNA
AK; 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; MB; NB; NS; NT; NU; ON; PE; QC; SK; YT; nearly worldwide
[WildflowerSearch map]
[BONAP county map]
from FNA
AK; AZ; CA; CO; CT; IA; ID; IL; IN; KS; MA; ME; MI; MN; MT; ND; NE; NH; NJ; NM; NV; NY; OH; OR; PA; RI; SD; UT; VT; WA; WI; WV; WY; AB; BC; MB; NB; NF; NS; NT; ON; PE; QC; SK; YT; Eurasia
[WildflowerSearch map]
[BONAP county map]
Discussion

Three hybrids, Potamogeton perfoliatus × P. pusillus (= P. × mysticus Morong), P. friesii × P. pusillus (= P. × pusilliformis Fisher [P. × intermedius Fischer]), and P. obtusifolius × P. pusillus (= P. × saxonicus Hagström), have been described.

Subspecies 3 (3 in the flora).

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

Potamogeton natans is the common floating-leaved pondweed of the north temperate ure areas. It is essentially circumboreal and can easily be identified by floating leaves that are almost always cordate at the base of the blade, the petiole with a short band of light tissue at its apex, and the submersed phyllodial leaves. Also, the apex of the petiole usually is bent so that the blade appears oriented in the opposite direction from which the petiole appears to be oriented.

One hybrid, Potamogeton natans × P. nodosus (= P. × schreberi Fischer [P. × perplexus A. Bennett]), has been described.

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

Key
1. Leaf blade 1-veined, subulate, 0.2–0.7 mm wide; New England and s Quebec.
subsp. gemmiparus
1. Leaf blade 1–5-veined, acute to obtuse, 0.2–2.5 mm wide; widespread throughout North America.
→ 2
2. Mature fruits obovoid, sides concave; beak toward adaxial edge, rarely median; peduncles filiform to cylindric, 1–3 per plant; inflorescences interrupted; leaf blade with 0–2 rows of lacunae along midrib, apex acute, rarely apiculate, rarely with bristle; stipules connate.
subsp. pusillus
2. Mature fruits widest at middle or ovoid, sides rounded; beak median, not toward adaxial edge; peduncles cylindric, more than 3 per plant; inflorescences continuous; leaf blade with 1–5 rows of lacunae along midrib, apex acute to obtuse; stipules convolute.
subsp. tenuissimus
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. nodosus, P. oakesianus, P. oblongus, P. obtusifolius, P. ogdenii, P. perfoliatus, P. praelongus, P. pulcher, 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. illinoensis, 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
Subordinate taxa
P. pusillus subsp. gemmiparus, P. pusillus subsp. pusillus, P. pusillus subsp. tenuissimus
Name authority Linnaeus: Sp. Pl. 1: 127. 1753 (as pusillum) Linnaeus: Sp. Pl. 1: 126. (1753)
Web links