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.Cultivation: The preference is full or partial sun, wet conditions (including 1-2' of water), and soil that is muddy, sandy, or gravelly. Locations with strong currents or wave action should be avoided.
Range & Habitat: The native Giant Bur-Reed is occasional in most areas of Illinois, except the southeast, where it is absent (see Distribution Map). Habitats include marshes, fens, swamps, borders of ponds and slow-moving rivers, and sloughs. Generally, Giant Bur-Reed is found in less disturbed wetlands with fertile soil or mineral-rich water.
Faunal Associations: A small number of insects are known to feed on Giant Bur-Reed and other Sparganium spp. These species include the aquatic leaf beetles Donacia confluenta, Donacia fulgens, Donacia parvidens, and Donacia subtilis; Sphenophorus australis australis (Cattail Billbug); and caterpillars of the moths Archanara laeta (Red Sedge Borer), Bellura obliqua (Cattail Borer Moth), and Plusia putnami (Putnam's Looper). Some of these insects also feed on cattails and other emergent or floating aquatic plants. The seeds of Giant Bur-Reed and other Sparganium spp. are readily consumed by many ducks and other wetland birds (see Bird Table for a listing of these species). Muskrats will consume the entire plant, and sometimes the foliage is browsed by White-Tailed Deer.
Photographic Location: Cowle's Bog at the Indiana Dunes National Lakeshore in NW Indiana. This wetland is actually a fen.
Comments: Giant Bur-Reed is the largest and most common Sparganium sp. in Illinois. It is also easy to identify during the flowering period because each one of its pistillate flowers usually has 2 styles, rather than a single style. Its achenes are also distinctive because of their obconic-angular shape; other Sparganium spp. within the state have achenes with more ellipsoid shapes. This interesting plant should be used in wetland restorations more often.