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Hill's pondweed

potamot de l'ilenissei, Yenisei River pondweed, Yenissei River pondweed

Cauline stems

slightly compressed, without spots, 30–60 cm;

glands rare, when present, brown to green, 0.1–0.3 mm diam.

compressed-filiform, without spots, to 50 cm;

glands white, 0.3–0.5 mm diam.

Turions

terminal, rare, 2.8–3 cm × 1.5–3 mm, soft;

leaves ± 2-ranked;

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

inner leaves undifferentiated.

lateral, common, 3.5–9.5 cm × 2–5 mm, soft;

leaves ± 2-ranked;

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

inner leaves undifferentiated.

Leaves

submersed, ± spirally arranged, sessile, delicate;

stipules persistent, inconspicuous, convolute, free from blade, white to light brown, not ligulate, 0.7–1.6 cm, slightly fibrous, rarely shredding at tip, apex obtuse;

blade pale green to olive-green, linear, not arcuate, 2–6 cm × 0.6–2.5(–4) mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, apiculate to bristle-tipped or rarely blunt, lacunae in 1–2 rows each side of midrib;

veins 3.

submersed, ± spirally arranged, sessile, flaccid;

stipules deliquescent, inconspicuous, convolute, free from blade, pale brown, not ligulate, 1–2 cm, not fibrous, not shredding, apex obtuse;

blade dark green, linear, not arcuate, 3.5–9.5 cm × 1.5–2 mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, rounded or nearly acute to mucronate, lacunae in 1–2 rows each side of midvein;

veins 9–17.

Inflorescences

unbranched, emersed;

peduncles not dimorphic, axillary and/or terminal, erect to ascending, rarely recurved, slightly clavate, 6–13.5 mm;

spikes not dimorphic, globose, (2–) 4–7 mm.

unbranched, emersed;

peduncles not dimorphic, axillary, erect, cylindric, 1.7–3.5 cm;

spikes not dimorphic, cylindric, 10–30 mm.

Fruits

brown to light greenish brown, ovoid to orbicular, turgid, sessile, abaxially and laterally keeled (3-keeled), 2.3–4 × 2–3.2 mm, lateral keels without points;

beak erect, 0.3–0.7 mm;

sides without basal tubercles;

embryo with 1 full spiral.

sessile, reddish brown, oblong-obovoid, compressed, abaxially ridged, not laterally keeled, 3–4 × 1.5–2 mm;

beak nearly erect, 0.3–0.5 mm;

sides without basal tubercles;

embryo with 1 full coil.

Chromosome number

unknownnot available.

Rhizome(s)

absent.

absent.

Potamogeton hillii

Potamogeton subsibiricus

Phenology Flowering and fruiting summer. Fruiting early summer–late summer.
Habitat Alkaline waters of marshes, ponds, lakes, and slow-moving streams Shallow water of ponds and lakes
Elevation 50–400 m (200–1300 ft) 0–915 m (0–3000 ft)
Distribution
from FNA
CT; MA; MI; NY; OH; PA; VA; VT; WI; ON
[WildflowerSearch map]
[BONAP county map]
from FNA
AK; MB; NT; NU; ON; QC; YT; Siberia
[BONAP county map]
Discussion

Potamogeton hillii is an easily recognized species either in fruit or when sterile. The leaf blade has a bristle tip and five or fewer veins. Those characters combined with the usual absence of nodal glands will separate this species from all other North American linear-leaved species. Ecologically, it is consistently found in more alkaline waters than any other North American pondweed. A study of 35 localities established the mean to be 124.1 mg/l CaCO3 (C. B. Hellquist 1984).

(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. 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
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. tennesseensis, P. vaseyi, P. zosteriformis
Synonyms P. porteri P. porsildiorum
Name authority Morong: Botanical Gazette 6: 290, fig. 3. (1881) Hagström: Kongl. Svenska Vetenskapsakademiens Handlingar n.s. 44:555(5):84. (1916)
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