Potamogeton richardsonii (Richardson's Pondweed)

Plant Info
Also known as:
Genus:Potamogeton
Family:Potamogetonaceae (Pondweed)
Life cycle:perennial
Origin:native
Habitat:part shade, shade, sun; shallow to 15 feet deep water; soft to hard water lakes, ponds, slow flowing rivers, creeks, sloughs
Bloom season:August - September
Plant height:6 to 40 inches
Wetland Indicator Status:GP: OBL MW: OBL NCNE: OBL
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: 4-petals Flower shape: indistinct Cluster type: spike

[photo of flowers] Dense cylindrical spike held above the surface of the water, ½ to 1½ inches (to 4 cm) long at the tip of the stem and arising from the upper leaf axils. Spikes have 6 to 12 whorls of flowers, each flower with a 4-parted style surrounded by 4 stamens, each stamen with a green, ladle-shaped, sepal-like appendage

Leaves and stems: Leaf attachment: alternate Leaf type: simple

[photo of leaves] Leaves are all submersed and more or less spirally arranged along the stem though may appear alternately attached on opposite sides of the stem (2-ranked); no floating leaves are produced. Blades are thin, usually bright green, lance to egg-shaped, 2/3 to 5+ inches long, ¼ to 1+ inches (5 to 28 mm) wide, mostly pointed at the tip, toothless, crinkly or wavy along the edges, with a prominent midvein flanked by 13 to 33 lateral veins, 3 to 5 of which are more prominent than the rest.

[photo of shredding stipules and clasping leaf bases] Leaf bases are stalkless and clasp the stem. At the base of the leaf is a whitish, membranous appendage (stipule), not connected to the leaf blade, up to about 1 inch long, soon shredding into persistent fibers. Stems are round, usually branched, straw-colored to green. Colonies may be formed from spreading rhizomes. Vegetative buds (turions) are not produced. Glands at the leaf nodes are absent.

Fruit: Fruit type: seed without plume

Fruit is a dry seed (achene), the flowering spikes forming densely packed seed heads, greenish-brown when mature. Achenes are irregularly oval, 2.2 to 4.2 mm long, and lack conspicuous keels. The prominent beak is .4 to .7 mm long and erect.

Notes:

Richardson's Pondweed is one of the most common Pondweeds in Minnesota, found in hard to soft water, quiet or flowing, to depths of 15+ feet. It is recognized by its clasping leaves up to 5 inches long, up to 1 inch wide, with wavy or crinkled edges, 13 to 33 veins and usually a pointed tip; persistent, whitish, fibrous stipules not attached to the leaf blade and usually less than 1 inch long; achenes 2.2 to 4.2 mm long that lack obvious keels. Leaves may be crowded especially on the upper stem and floating leaves are absent.

While there is some resemblance to the submersed leaves of other Pondweeds, the clasping leaves with a pointed tip, fibrous stipules, and achenes without keels should distinguish P. richardsonii from the rest. Most similar is Potamogeton praelongus, which has larger leaves (to 8 inches long) with a boat-shaped tip (splits in two when pressed), usually a decidedly zig-zag stem, stipules 1 to 4 inches long that are only sometimes fibrous, and larger achenes (4 to 5.7 mm long) with a distinct keel along the back.

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More photos

Photos by Peter M. Dziuk taken in Beltrami, Clay and Lake counties.

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