Aquatic and Wetland Vascular Plants of the Northern Great Plains
62. Cyperaceae, the Sedge Family
11. Scirpus L. -- Bulrush3. Scirpus fluviatilis (Torr.) A. Gray -- River bulrush
Stout perennial 7-15 dm tall, often forming large colonies by the extensive rhizomes; culms erect, sharply trigonous, arising from black tuberous thickenings on the rhizomes. Leaves sheathing most of the length of the culm; blades ascending, the upper ones commonly surpassing the inflorescence, 6-15 mm wide; sheaths convex at the mouth, the ventral nerves abruptly divergent at the summit; involucral bracts 3-5, foliaceous and spreading, the longest to 30(45) cm long. Inflorescence terminal, containing 10-20 spikelets, several of the spikelets nearly sessile in 1 or 2 clusters, others solitary or in glomerules of 2-5 at the ends of pedicels to 8 cm long; spikelets 10-25(35) mm long, 6-12 mm thick; scales golden brown, puberulent on the back, 6-9 mm long, acute to bifid, aristate, the awn 1-3 mm long, curved; perianth of 6 unequal, white to coppery bristles, mostly equaling or exceeding the achene body; stamens 3, strongly exsert at anthesis, with conspicuous elongate yellow anthers 4-6 mm long, the filaments flattened, often persistent to the achene; styles trifid, strongly exsert. Achenes tan to grayish-green or grayish-brown, often mottled, trigonous, 3-4.5 mm long, 2-2.8 mm wide, with a beak 0.2-0.5 mm long. Jun--Aug. Usually in shallow water of streams, ditches, marshes, lakes and ponds; common except in the w part; (Que. to WA, s to VA, MO, KS and CA).
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