Long-Leaved Pondweed
Potamogeton nodosus
Pondweed family (Potamogetonaceae)

Description: This aquatic perennial plant consists of a submerged branching stem about 2-8' long that has both submerged and floating leaves. The branching stem is light green to pale yellow, terete to slightly compressed, and glabrous. Along its length, there are alternate submerged leaves about 1-5" long and -1" across. These submerged leaves are narrowly oblong-elliptic to lanceolate-elliptic, tapering gradually toward both their tips and their bases; their margins are smooth. The submerged leaves have 7-15 parallel veins. The petioles of the submerged leaves are -5" long. At the bases of the submerged petioles, there are linear-lanceolate stipules about 1-3" long. The submerged leaves and stipules are green or brown and hairless; they eventually disintegrate as new leaves are produced. Toward the tips of the stems, there are alternate or opposite floating leaves about 2-6" long and -1" across. The floating leaves are oblong-elliptic in shape, tapering to wedge-shaped or narrowly rounded bottoms and flat tips. The floating leaves have 9-17 parallel veins and smooth margins; their upper surfaces are green, hairless, and shiny. The petioles of these leaves are 1-10" long; at the bases of these petioles, are stipules that are similar to those of the submerged leaves. From the axils of floating leaves, spikes of flowers are produced that are exerted above the surface of the water. These floral spikes are -2" long, olive green to reddish brown, and cylindrical in shape. The peduncles of these flowers are 1-6" long, hairless, and terete. The flowers are packed densely together along the sides of each spike. Each greenish flower is about 1/8" across, consisting of 4 rounded sepals that taper to narrow bases, 4 stamens, and a pistil with a single style. The blooming period can occur from late spring to late summer and lasts about 2 weeks. Afterwards, the flowers are replaced by reddish brown seeds about 3-4 mm. long and 2.5-3 mm. across. Each chunky seed has a keel on one side and a pair of parallel ridges along the opposite side; there is a short beak at its apex. The root system is fibrous and rhizomes. Colonies of plants often develop in shallow water.

Cultivation: The preference is full sun, warm standing water up to 4' deep, and a mucky bottom. This plant can spread aggressively in shallow water.

Range & Habitat:
The native Long-Leaved Pondweed is common throughout Illinois. In addition to North America, this plant occurs in South America and Eurasia. Habitats consist of ponds, quiet harbors of lakes, slow-moving streams, and deep ditches with standing water.

Faunal Associations: Some insects feed on the foliage of pondweeds (Potamogeton spp.). These species include stylish aquatic leaf beetles (e.g., Neohaemonia flagellata, Neohaemonia melsheimeri, and Neohaemonia nigricornis), which are specialist feeders of pondweeds. Other insects feeders include the aquatic leaf beetle Donacia hirticollis, Rhopalosiphum nymphaeae (Waterlily Aphid), and the caterpillars of such moths as Munroessa icciusalis (Pondside Pyralid Moth), Parapoynx obscuralis (Obscure Pondweed Moth), and Synclita obliteralis (Waterlily Leaf Cutter). The caterpillars of these moths form protective cases that are made of plant parts. Such wetland birds as ducks, swans, and rails feed on either the foliage or seeds of pondweeds. These bird species include such ducks as the Redhead, Canvasback, Wood Duck, Ring-Necked Duck, Black Duck, and many others (see the Bird Table for a more complete listing of these species). Pondweeds are also eaten by many turtles (Lagler, 1943; Moll, 1976; Ernst, Barbour, & Lovich, 1994); this includes the Snapping Turtle (Chelydra serpentina), Painted Turtle (Chrysemys picta), Blanding's Turtle (Emys blandingii), Ouachita Map Turtle (Graptemys ouachitensis), False Map Turtle (Graptemys pseudogeographica), Musk Turtle (Sternotherus odoratus), and Slider (Trachemys scripta). Muskrats also feed on the lower stems and other parts of these aquatic plants (Hamerstrom & Blake, 1939). Pondweeds provide protective cover for fish and other forms of aquatic wildlife.

Photographic Location: A pond at the Arboretum of the University of Illinois in Urbana, Illinois.

Comments: Long-Leaved Pondweed belongs to a group of conspicuous pondweeds (Potamogeton spp.) that produce relatively broad floating leaves. Other pondweeds produce leaves that are narrow (linear in shape) or all of their leaves are normally submerged. Among the pondweeds with broad floating leaves, Long-Leaved pondweed has floating leaves that are longer than most (often exceeding 3" in length) and their bases are wedge-shaped or narrowly rounded, rather than broadly rounded or cordate. Furthermore, the submerged leaves of this species, when they are present, are useful in identification. They have relatively long petioles for submerged leaves (sometimes exceeding 3" in length) and in shape they are a more narrow version of the floating leaves of this species. Other pondweeds have submerged leaves with shorter petioles, or their submerged leaves are linear in shape, or they are more broad in shape. This common pondweed has been referred to as Potamogeton americanus (American Pondweed) in the past.