IUCN threat status:

Least Concern (LC)

Comprehensive Description

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Description

This aquatic plant forms branched leafy stems up to 3' long. The slender stems are light to medium green, narrowly terete (filiform) to slightly flattened, and glabrous. Alternate leaves are spaced about 1–7 cm. (½–2¾") apart along the stems, becoming more crowded toward their tips. Mature leaves are 1.5–6 cm. in length (averaging about 2–2.5 cm. or ¾–1") and 0.5–1.5 mm. across; they are medium green or olive green, linear in shape, smooth along their margins, glabrous, and sessile. Leaf venation is parallel; each leaf has a single central vein and sometimes 2 lateral veins that are visible using a 10x hand-lens. Both the stems and leaves are soft and flexible, rather than stiff. At some leaf bases along the stems, there are pairs of translucent glands that are slightly swollen and difficult to see. In addition, membranous sheaths about 2.5–9 mm. in length wrap around the stems at the bases of young leaves; they are usually light brown. These sheaths are initially tubular in shape, but they soon split along one side and later become completely detached from the stems without becoming fibrous. Both terminal and axillary spikes of flowers are produced, usually in considerable abundance; they are often held slightly above the water surface. These floral spikes are 3-10 mm. long and 3-4 mm. across, consisting of 1-4 interrupted whorls of flowers. Each flower is about 2 mm. across, consisting of 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 12-52 mm. (½–2") long, narrowly terete to slightly flattened, pale green, and glabrous; they are either straight or curve upward toward the water surface. The blooming period occurs during the summer or early fall, lasting 2-4 weeks for a colony of plants. The flowers are cross-pollinated primarily by the wind and, to a lesser extent, by water currents. Afterward, fertile flowers are replaced by achenes that are initially green, but they later become brown with maturity. Individual achenes (while still fresh) are 1.5–2.5 mm. in length, 1.0-2.0 mm. across, and somewhat flattened; they are somewhat obovoid (where one edge is flat, while the other edge is convex) with short stout beaks at their apices. The sides of fresh achenes are convex, while the sides of dried-out achenes are flat to slightly concave. These achenes lack significant keels. The root system is fibrous. This plant reproduces vegetatively by the breakage of leafy stems that can form roots in the mud. It also reseeds itself. Sometimes colonies of plants are formed at favorable sites.

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© John Hilty

Source: Illinois Wildflowers

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