Flower:

Cylindrical spike held above the surface of the water, ¼ to 1/3 inch (to 8 mm) long at the tip of the stem and arising from the axils of floating leaves. Spikes have 1 to 4 whorls of flowers, each flower with a 4-parted style surrounded by 4 stamens, each stamen with a yellowish to orange-brown, ladle-shaped, sepal-like appendage.

Leaves and stems:

Both submersed and floating leaves are produced, though floating leaves are often few and may be absent. Floating leaves are opposite or spirally arranged, firm, green to yellowish-brown, oval-elliptic to somewhat spatula-shaped, to ~½ inch (1.5 cm) long, up to 1/3 inch (8 mm) wide, toothless, rounded at the tip, usually tapering at the base to a stalk more or less as long as the blade but may be up to twice as long. Blades have 5 to 9 veins, with oval-elliptic, hollow (lacunar) cells between the veins.

Submersed leaves are spirally arranged, bright green to reddish-brown, thin, thread-like, ¾ to 3+ inches (to 8 cm) long, .2 to 1 mm wide, pointed at the tip, stalkless, and usually have 1 vein, occasionally with a pair of obscure lateral veins, and lacking lacunar cells along the midvein. At the base of the leaf is a pale, membranous appendage (stipule), not connected to the leaf blade, blunt at the tip, somewhat fibrous later in the season, less than ½ inch (to 12 mm) long. Glands at the leaf nodes may or may not be present.

Vegetative buds (turions) are commonly produced at the tips of short, lateral branches and some leaf axils; turions are up to 1 inch long, slender, with 2 or 3 outer leaves on each side, the inner leaves usually rolled into a firm structure. Stems are very slender and round in cross-section, freely branched.

Fruit:

Fruit is a dry seed (achene), the flowering spikes forming tightly to somewhat loosely packed seed heads, greenish-brown when mature.

Achenes are irregularly oval to nearly round, 1.5 to 2.5 mm long, with or without a low, smooth keel along the back edge; lateral keels are absent. The beak is erect and up to .5 mm long.

Notes:

Vasey's Pondweed is occasional in northern and central Minnesota, where it reaches the western edge of its range. It is usually found in the quiet, shallow waters of soft water lake margins with sandy or mucky substrates, usually in less than 4 feet of water. It is considered rare in much of its range and was thought to be rare in Minnesota as well. According to the DNR, it was listed as a Special Concern species in 1984 but was delisted in 2013 after biological surveys found it in over 120 lakes.

Potamogeton vaseyi is a very delicate species, distinguished by its thread-like submersed leaves 1 to 3 inches long, .2 to 1 mm wide, 1 to 3-veined; stipules not connected to the leaf and becoming somewhat fibrous; slender turions at the tips of short branches or in leaf axils; achenes 1.5 to 2.5 mm long with or without a low keel along the back and lacking lateral keels. Floating leaves should be present on at least some plants in a population; they are quite small (often about the size of a dime) on stalks about as long as the blade and are spirally arranged or in opposite pairs. Flowering/fruiting spikes are found on plants with floating leaves where the turions are produced on vegetative plants. P. vaseyi is also an annual, where most other Pondweeds are perennial.

There are several Pondweeds with thread-like submersed leaves not more than 1 mm wide, all of which are more rare than P. vaseyi. Potamogeton bicupulatus and P. diversifolius both have flowering spikes in the axils of submersed leaves and their stipules are attached to the leaf blades. P. oakesianus submersed leaves are longer (2 to 6 inches), floating leaves are also larger (¾ to 1½ inches long) and are pointed at the tip. P. confervoides has no floating leaves and flowering spikes are emersed at the tip of the stem. P. berchtoldii (a.k.a. P. pusillus subsp. tenuissimus) sometimes has submersed leaves less than 1 mm wide, but has no floating leaves; flowering spikes are in the axils of submersed leaves.