Vasey's Pondweed

All of the original material of Potamogeton lateralis Morong, including the collection designated as the lectotype, has been studied (C. B. Hellquist et al. 1988). Every specimen, was a mixed collection of P. pusillus and P. vaseyi. Based on the results of the study, P. lateralis is taxonomically nomenclaturally invalid and should be rejected.

Potamogeton vaseyi is an uncommon species that has submersed leaves very similar to P. pusillus subsp. gemmiparus. Floating leaves apparently are present only when the species is fertile, and the species often grows intermixed with that subspecies. Collections are consequently often a mixture of the two taxa. Also, sterile collections of either taxon can easily be mistaken for the other.

Rhizomes absent. Cauline stems terete, without spots, 2--5 cm; glands absent. Turions common, axillary, 0.5--2 cm ´ 0.5--1.2 mm, soft; leaves ± 2-ranked; outer leaves 2--3 per side, base not corrugate, apex acute; inner leaves undifferentiated or rolled into tight, hardened structure. Leaves submersed, or both submersed and floating, ± spirally arranged. Submersed leaves sessile, delicate; stipules persistent, inconspicuous, convolute, free from blade, green to brown, not ligulate, 0.4--1.2 cm, not fibrous, not shredding at tip, apex attenuate; blade light green, linear-filiform, not arcuate, 2--8 cm ´ 0.1--1 mm, bases slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, acute to almost bristle-tipped, lacunae present, rarely absent, 0--2 rows each side of midvein; veins 1(--3). Floating leaves: petioles continuous in color to apex, 5--25 mm; blade adaxially greenish brown, elliptic, spatulate, or obovate, 0.6--1.5 cm ´ 3--8 mm, base acute, apex obtuse; veins 5--9. Inflorescences unbranched, emersed; peduncles not dimorphic, terminal, ascending in flower, recurved in fruit, cylindric, 5--30 mm; spikes not dimorphic, cylindric or moniliform, 6--8 mm. Fruits sessile, green to brown, obliquely round-obovoid, compressed, abaxially keeled, not laterally keeled, 1.5--2.5 ´ 1.2--1.6 mm; beak erect, 0.3--0.5 mm; sides without basal tubercles; embryo with 1 full spiral. 2n = 28.

N.B., Ont., Que.; Conn., Ill., Ind., Iowa, Maine, Mass., Mich., Minn., N.H., N.J., N.Y., Ohio, Pa., R.I., Vt., Wis.

Flowering and fruiting summer--fall.

Quiet waters of lakes, ponds, and rivers; 50--500m.

Potamogeton lateralis Morong, Bot. Gaz. 5 : 51. 1880
Stem slender, much branched; floating leaves petioled; blades coriaceous, ellipticlanceolate, acute or obtuse at the apex, narrowly decurrent at the acute base, 6.5-11 mm. long, 1.8-3.1 mm. wide ; petioles as long as the leaf-blades or shorter; stipules axillary and free from the petioles, obtuse, 2.2-4 mm. long; submerged leaves capillary, 0.4-O.9 mm. wide, 1.8-3.4 cm. long; spikes 2.4-6 mm. long, few-flowered; peduncles 9-15 mm. long, as thick as the stem ; nutlets smooth, 2-grooved on the back ; embryo an incomplete spiral, the straight apex pointing directly towards the base. '
Type locality : Dedham, Massachusetts.
Distribution : Massachusetts and Connecticut.

Potamogeton vaseyi Robb. in A. Gray, Man. ed. 5. 485. 1867
Potamogeton Vaseyi latifolius Morong, Mem. Torrey Club 3 2 : 44. 1893.
Stem slender, much branched; floating leaves petioled; blades coriaceous, spatulateovate, 7-12 mm. long, 4-6 -mm. wide, rounded at the apex, acute and narrowly decurrent at the base ; petioles as long as the leaf -blades or shorter ; stipules axillary and free from the petioles, acute, 3-5 mm. long; submerged leaves slender, capillary, 0.5-0.9 mm. wide, 2-3.6 cm. long; spikes sometimes interrupted, 5-11 mm. long; peduncles 5-14 mm. long, as thick as the stem; nutlets smooth or slightly pitted, 3-keeled; embryo a complete spiral, the curved apex pointing inside the base.
Type locality : Near Ringwood, McHenry County, Illinois. Distribution: Quebec to Wisconsin, south to southern New York.

Potamogeton vaseyi, common name Vasey's pondweed, is a species of plant found in North America. It is listed as an endangered species in Indiana, Massachusetts, and Pennsylvania, and is listed as threatened in Connecticut, Maine, Michigan, and New Hampshire, and as presumed extirpated in Ohio.