Hill's Pondweed

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).

Rhizomes absent. Cauline stems slightly compressed, without spots, 30--60 cm; glands rare, when present, brown to green, 0.1--0.3 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. 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. 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. 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. Chromosome number unknownnot available.

Ont.; Conn., Mass., Mich., N.Y., Ohio, Pa., Vt., Va., Wis.

Flowering and fruiting summer.

Alkaline waters of marshes, ponds, lakes, and slow-moving streams; 50--400m.

Potamogeton porteri Fernald

Potamogeton hillii Morong, Bot. Gaz. 6 : 290. 1881
Stem slender, branched, without propagating buds ; leaves all submerged, linear, acute, cuspidate or aristate at the apex, 2.5-6 cm. long, 2-2.8 mm. wide, with 2 glands at the base or glandless, 3-nerved, the lateral nerves less prominent than the midrib and remote from it; stipules scarious, 0.6-1.8 cm. long, aristate or rarely obtuse at the apex, axillary and free from the leaf-bases ; spikes few-flowered; peduncles scarcely more than 1.5 cm. long, as thick as or a little thicker than the stem ; nutlets smooth, 3-keeled, the middle keel prominent and undulate or crisped, the lateral keels inconspicuous ; style projecting at least 1 mm. from the body of the fruit and crowned with a depressed-globose stigma; embryo a complete spiral, the curved apex pointing inside the base.
Type locality : New York and Michigan.
Distribution : New York to Michigan and I,ake Superior, south to Pennsylvania and Missouri.

Potamogeton hillii, common name Hill's pondweed, is a species of plant found in North America. It is listed as endangered in Connecticut, Ohio, and Pennsylvania. It is listed as a special concern in Massachusetts and as threatened in Michigan and New York (state).