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blunt-leaf pondweed, potamot à feuilles obtuses

small pondweed

Rhizomes

absent.

absent.

Cauline stems

slightly compressed, without spots, 35–90 cm;

glands yellow-green to gold, 0.2–1 mm diam.

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.

Turions

terminal, abundant, 3.5–7.8 cm × 2.3–5.1 mm, soft;

leaves ± 2-ranked;

outer leaves 3–4 per side, base not corrugate, apex apiculate to obtuse;

inner leaves undifferentiated.

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.

Leaves

submersed, ± spirally arranged, sessile, flaccid;

stipules persistent, inconspicuous, convolute, free from blade, white, not ligulate, 0.6–1.8 cm, fibrous, rarely shredding at tip, apex obtuse;

blade light green to somewhat reddish, linear, not arcuate, 3–8.2 cm × 1–3.5 mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, obtuse or round-apiculate, lacunae in 1–3 rows each side of midrib;

veins 3.

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).

Inflorescences

unbranched, emersed;

peduncles not dimorphic, axillary, erect, rarely recurved, cylindric, 0.8–1.9(–4.2) cm;

spike not dimorphic, cylindric, 8–13 mm.

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.

Fruits

sessile, olive-green to brown, obovoid, turgid, abaxially keeled or not, laterally keeled or not, 2.5–3.6 × 1.7–2.4 mm, lateral keels when present without points;

beak erect, 0.8–1 mm;

sides without basal tubercles;

embryo with 1 full spiral.

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.

2n

= 26.

Potamogeton obtusifolius

Potamogeton pusillus

Phenology Flowering and fruiting summer–fall.
Habitat Medium- to low-alkaline waters of lakes and slow-flowing streams
Elevation 50–2000 m (200–6600 ft)
Distribution
from FNA
AK; CT; ID; MA; ME; MI; MN; MT; NH; NJ; NY; PA; RI; VT; WA; WI; WY; AB; BC; MB; NB; NB; NF; NS; NT; ON; PE; QC; SK; YT; Eurasia
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[BONAP county map]
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]
Discussion

Potamogeton obtusifolius is a distinctive linear-leaved species with the leaf blades round at the apex, especially when fruiting inflorescences 5–7 mm wide are present. This is unusually wide for one of the linear-leaved species.

Two hybrids, Potamogeton obtusifolius × P. pusillus (= P. × saxonicus Hagström) and P. friesii × obtusifolius (= P. × semifructus A. Bennett ex Ascherson & Graebner), have been described.

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

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.)

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. 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. 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
Subordinate taxa
P. pusillus subsp. gemmiparus, P. pusillus subsp. pusillus, P. pusillus subsp. tenuissimus
Name authority Mertens & W. D. J. Koch: in J. C. Röhling et al., Deutschl. Fl., ed. 3 1: 855. (1823) Linnaeus: Sp. Pl. 1: 127. 1753 (as pusillum)
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