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

blunt-leaf pondweed, potamot à feuilles obtuses

alpine pondweed, northern pondweed, potamot alpin, reddish pondweed

Cauline stems

slightly compressed, without spots, 35–90 cm;

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

terete, without spots, to 200 cm;

nodal glands absent.

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.

absent.

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 and floating or floating absent, ± spirally arranged.

Floating leaves

petioles continuous in color to apex, 0.1–1.2 cm;

blade reddish green, elliptic or oblanceolate to obovate or oblong-linear, 4–7(–10) cm × 10–25(–40) mm, base gradually tapering into petiole, apex obtuse or acute;

veins (7–)9–13(–15).

Submersed leaves

sessile, lax;

stipules persistent, inconspicuous, convolute, free from blade, light brown to reddish, not ligulate, (1.2–)1.5–2.5(–4) cm, not fibrous, not shredding at tip, apex blunt;

blade reddish green, oblong-linear to linear-lanceolate, not arcuate, 4.5–18(–25) cm × 5–20 mm, base rounded, without basal lobes, slightly clasping, margins entire, not crispate, apex not hoodlike, obtuse or acute, lacunae in 0–6 rows each side of midvein;

veins 7–9.

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, emersed;

peduncles not dimorphic, terminal or axillary, erect, cylindric, 3–10(–16) cm;

spikes not dimorphic, cylindric, 10–35 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.

pedicellate, tawny olive-green, obovoid, plump, turgid, abaxially keeled, laterally keeled or not, (2.5–)3–3.5 × (1.7–)2–2.4 mm, lateral keels when present without points;

beak abaxially curved, 0.5–0.9 mm;

sides without basal tubercles;

embryo with 1 full spiral.

Rhizome(s)

absent.

present.

2n

= 26.

= 52.

Potamogeton obtusifolius

Potamogeton alpinus

Phenology Flowering and fruiting summer–fall. Flowering early summer–fall.
Habitat Medium- to low-alkaline waters of lakes and slow-flowing streams Ponds, lakes, and slow-moving streams
Elevation 50–2000 m (200–6600 ft) 400–2500 m (1300–8200 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
[WildflowerSearch map]
[BONAP county map]
from FNA
AK; CA; CO; ID; MA; ME; MI; MN; MT; NH; NJ; NV; NY; OR; PA; SD; UT; VT; WA; WI; WY; AB; BC; MB; NB; NL; NS; NT; NU; ON; PE; QC; SK; YT; Greenland; Europe; Asia Eurasia
[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.)

Plants of Potamogeton alpinus often are red whenever taken from the water, a feature that makes this species quite distinctive.

Two varieties, Potamogeton alpinus var. tenuifolius and var. subellipticus, have been recognized in North America, based mainly on submersed leaf shape. Plants bearing both leaf types have been observed in the same population; hence the varieties are not recognized.

Four hybrids, Potamogeton alpinus × P. nodosus (= P. ×subobtusus Hagström), P. alpinus × P. gramineus (= P. xnericius Hagström), P. alpinus × P. praelongus (= P. ×griffithii A. Bennett), and P. alpinus × P. perfoliatus (= P. ×prussicus Hagström), 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. 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. 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, P. zosteriformis
Synonyms P. alpinus subsp. tenuifolius, P. alpinus var. subellipticus, P. alpinus var. tenuifolius, P. tenuifolius, P. tenuifolius var. subellipticus
Name authority Mertens & W. D. J. Koch: in J. C. Röhling et al., Deutschl. Fl., ed. 3 1: 855. (1823) Balbis: Misc. Bot. 13. (1804)
Web links