IUCN threat status:

Not evaluated

Comprehensive Description

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This perennial plant is an emergent aquatic about 2-6' tall, producing erect to ascending alternate leaves along the central stem. Both the stem and leaves are medium green and glabrous. The linear leaves are 1-5' long, ¼-¾" across, and smooth along their margins. Each leaf is keeled on one side, becoming flat toward its tip; venation is parallel. The central stem terminates in an inflorescence that is usually branched. On each branch of the inflorescence, there are 1-6 pistillate (female) flowerheads and 0-20 staminate (male) flowerheads. Except when a single pistillate flowerhead occurs on a short stalk, these flowerheads are sessile. The staminate flowerheads are located above the pistillate flowerheads on the same branches; all flowerheads are separated at intervals from each other. The branches of the inflorescence are medium green, glabrous, and terete; they have a tendency to bend where the pistillate flowerheads occur. The pistillate flowerheads are about ¾-1¼" across, globoid in shape, greenish, and prickly in appearance; the pistillate flowers are packed densely together in each head. Each pistillate flower consists of an ovary, several scale-like sepals (or sepaloid connectives), and a a style with 2 white stigmata (atypically with a single stigma). The greenish sepals are narrowly oblanceolate and either rounded or somewhat disintegrated along their upper margins. The staminate flowerheads are somewhat smaller in size than the pistillate flowerheads; they are globoid in shape, pale yellow during the bud stage, becoming bright white while blooming. The staminate flowers are packed densely together in each head; each staminate flower has 5 stamens with white filaments and yellow to brown anthers. At the base of each branch of the inflorescence, there is an ascending leafy bract that resembles the leaves, except it is more flat and smaller. Both the leaves and leafy bracts have basal sheaths. The blooming period occurs during the summer and lasts 2-3 weeks. The flowers are wind-pollinated. The pistillate flowers are replaced by achenes that become brown at maturity. Each achene has an obconic-angular body (5-10 mm. in length) with a beak at its apex (2-4 mm. in length). The root system is fibrous and rhizomatous; small tubers may occur as well. This plant reproduces by seed or by forming clonal offsets. Small colonies of plants are often produced.


Creative Commons Attribution Non Commercial 3.0 (CC BY-NC 3.0)

© John Hilty

Source: Illinois Wildflowers

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