Leafy Pondweed
Potamogeton foliosus
Pondweed family (Potamogetonaceae)

Description: This submerged aquatic plant consists of branching leafy stems up to 2' (0.75 m.) long. The slender stems are about 1 mm. across; they are pale green or pale yellowish green, glabrous, somewhat flattened, and flexible. Alternate leaves occur along unbranched areas of the stems, while either alternate or opposite leaves occur where the stems divide. These leaves are up to 6 cm. long (rarely longer) and about 1.5 mm. across (varying from 1.0-2.0 mm. across). The leaves are green or olive green, linear in shape, smooth along their margins, glabrous, and sessile, tapering to flat acute tips. The leaves are grassy in appearance, relatively soft, and flexible, lacking glands. Fused stipules occur at the leaf bases that are 8-20 mm. long and usually early-deciduous. Submerged floral spikes develop from some of the leaf axils on short peduncles. These floral spikes are 2-6 mm. long and up to 4 mm. across, each one consisting of a short dense cluster of flowers that is spherical to short-cylindrical in shape. Each flower is about 2 mm. across, consisting 4 green to greenish brown sepals (or sepaloid connectives), 4 stamens, and 4 pistils. The sepals are clawed (contract abruptly) at their bases. The peduncles are 3-12 mm. long and about 1 mm. across; they are pale green or pale yellowish green and somewhat flattened.

The blooming period occurs during mid- to late summer, lasting about 3 weeks for a colony of plants. The flowers are cross-pollinated by water currents. Afterwards, fertile flowers are replaced by achenes (up to 4 achenes per flower). These achenes are 1.25-2.25 mm. long and 1.00-1.75 mm. across; they are green to brownish green, ovoid-globoid in shape, somewhat flattened, smooth-sided, short-beaked, and keeled. The sharp keels of these achenes are winged and crested (appearing toothed). The bases of some achenes may have a minute tooth-like projection. This aquatic plant also produces narrow turions (winter buds) that are up to 1 cm. long and 2 mm. across. The root system is fibrous. Sometimes fibrous roots develop from the lower nodes of stems that are decumbent on bottom sediment. This aquatic plant can spread vegetatively from the breakage of leafy stems that drift in water to new areas.

Cultivation: The preference is full sun, shallow clear water that is stagnant or slow-moving, and bottom sediment containing silt, mud, and/or organic matter. Desirable water pH can be mildly acidic to alkaline. Leafy Pondweed (Potamogeton foliosus) can spread aggressively in some wetlands. However, this pondweed will decline in abundance when it occurs in water that is too muddy from suspended sediments, or that contains too much fertilizer (e.g., nitrogen and phosphorus) from agricultural or suburban run-off. The latter problem can cause excessive competition from filamentous algae.

Range & Habitat:
Leafy Pondweed (Potamogeton foliosus) is common in most areas of Illinois (see Distribution Map), where it is native. This pondweed is widely distributed in North America. Habitats consist of spring-fed streams, slow-moving creeks, ponds, sheltered areas of lakes, drainage canals, and ditches that contain water during most of the year. This pondweed adapts to shallow water better than most pondweed species (Potamogeton spp.) and it is often common in disturbed wetland habitats, particularly when there is protection from waterfowl or fish.

Faunal Associations: The larvae of some shore flies (Ephydridae), including Hydrellia ascita and Hydrellia cruralis, feed on the submerged leaves of this pondweed, as do the larvae of Parapoynx allionealis (Watermilfoil Leafcutter Moth). Larvae of the aquatic beetles Neohaemonia flagellata, Neohaemonia melsheimeri, and Neohaemonia nigricornis feed on the submerged stems and roots of various pondweeds (Potamogeton spp.). Because of its soft fine foliage and relative abundance, Leafy Pondweed is one of the more important sources of food for vertebrate animals among the various pondweeds. Both the seeds and foliage are eaten by many ducks, geese, and swans (see Waterfowl Table). Submerged pondweeds are also eaten by carp, catfish, and other kinds of fish (see Forbes, 1888), and they are eaten by such turtles as Chelydra serpentina (Snapping Turtle), Chrysemys picta (Painted Turtle), Emydoidea blandingii (Blanding's Turtle), Graptemys ouachitensis (Ouachita Map Turtle), Graptemys pseudogeographica (False Map Turtle), Sternotherus odoratus (Musk Turtle), and Trachemys scripta (Slider); see Lagler (1943) and Ernest et al. (1994). Muskrats also feed on these plants (Hamerstrom & Blake, 1939; Martin et al., 1951/1961). Because Leafy Pondweed often forms dense mats of leafy stems, it provides good cover for minnows, aquatic insects, and other aquatic organisms.

Photographic Location:
Photographed plants were collected from a ditch in Savoy, Illinois.

Comments: This common pondweed has a rather grassy appearance. It can be difficult to distinguish Leafy Pondweed (Potamogeton foliosus) from other submerged pondweeds (Potamogeton spp.) with linear leaves unless the floral spikes are present. Compared to these species, the floral spikes of Leafy Pondweed are very short and densely flowered, and they have shorter peduncles (3-12 mm.). In addition, the leaves of Leafy Pondweed usually lack visible glands and its stems are flattened, rather than terete. The achenes of this pondweed are also distinctive because of their winged crested keels, which are visible to the naked eye. Different varieties of Leafy Pondweed have been described across its geographic range, although they tend to intergrade. In Illinois, it is the typical variety (Potamogeton foliosus foliosus) that is commonly encountered.