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small pondweed

eel-grass pondweed, flat-stem pondweed, potamot zostériforme

Rhizomes

absent.

absent.

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.

conspicuously flattened ("wing-flattened"), without spots, 60–120 cm;

glands absent or rarely present, when present, gold, 0.3 mm diam.

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.

common, terminal or lateral, 4–7.5 × 2–4.5 cm, firm;

leaves ± 2-ranked;

outer leaves 3–4 per side, base not corrugate, apex acute;

inner leaves undifferentiated.

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).

submersed, ± spirally arranged, sessile, rigid;

stipules persistent, conspicuous, convolute, free from blade, white, not ligulate, 1.5–3.5 cm, fibrous, shredding at tip, apex obtuse to acuminate;

blade light green, linear, not arcuate, 10–20 cm × 2–5 mm, base rounded, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, blunt, acuminate, or bristle-tipped, lacunae absent;

veins 15–35.

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, occasionally recurved, cylindric, 2–5 cm;

spikes not dimorphic, cylindric, 15–30 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.

light green to olive-green, quadrate-oblong or nearly orbicular, turgid, sessile, with abaxially keeled, not laterally keeled, 4–5 × 3–3.5 mm, keel winglike;

beak erect, 0.6–1 mm;

sides without basal tubercles;

embryo with 1 full spiral.

2n

= 52.

Potamogeton pusillus

Potamogeton zosteriformis

Phenology Flowering summer–fall.
Habitat Lakes, ponds, and slow streams
Elevation 0–15003000 m [0–49222400 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; CA; CT; IA; ID; IL; IN; KS; MA; ME; MI; MN; MT; ND; NE; NH; NJ; NV; NY; OH; OR; PA; SD; UT; VT; WA; WI; WY; AB; BC; MB; NB; NF; NS; NT; ON; PE; QC; SK; YT
[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.)

One hybrid, Potamogeton zosteriformis × P. strictifolius, has been described and has been given the name P. ×haynesii Hellquist & G. E. Crow and is known from northern Michigan, Minnesota, Vermont, and southern Canada.

(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. 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
Subordinate taxa
P. pusillus subsp. gemmiparus, P. pusillus subsp. pusillus, P. pusillus subsp. tenuissimus
Synonyms P. zosterifolius subsp. zosteriformis, P. zosterifolius var. americanus
Name authority Linnaeus: Sp. Pl. 1: 127. 1753 (as pusillum) Fernald: Memoirs of the american academy of arts and science n.s. 17:36. (1932)
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