Scirpus diffusus Schuyler

Plants spreading; rhizomes elongate to 12 cm. Culms: fertile ones upright or nearly so; nodes without axillary bulblets. Leaves 4–10 per culm; sheaths of proximal leaves green or brownish; proximal sheaths and blades with septa few, inconspicuous; blades 11–30 cm × 5–8 mm. Inflorescences terminal, rarely also with 1 lateral inflorescence from distal leaf axil; rays spreading or ascending, smooth, without axillary bulblets; bases of involucral bracts green or speckled with red, not glutinous. Spikelets in dense clusters of (1–)3–14 (largest cluster with 8 or more), spikelets sessile, ovoid to lance-ovoid, 3–6 × 1.5–2.5 mm; scales green to brown or black, elliptic, 1.4–2.6 mm, apex mucronate or rarely short-awned, mucro or awn 0.1–0.3 mm. Flowers: perianth bristles persistent, 6, slender, contorted (or some almost straight), shorter than to 1.5 times as long as achene, if long then contorted and not projecting beyond achene, with closely arranged retrorse, thin-walled, round-tipped barbs in distal 1/2, enclosed within scales; styles 3-fid. Achenes pale brown, obovate or elliptic in outline, plano-convex, 0.9–1.3 × 0.7–0.8 mm.

Calif.

Fruiting summer (Jul).

Moist meadows; 300–2500m.

Scirpus diffusus is a species of flowering plant in the sedge family known by the common name umbrella bulrush. It is endemic to California, where it can be found in several of the high mountain ranges from the Klamath Mountains to the Sierra Nevada. It grows in wetland habitat and other moist areas, such as mountain meadows. It is similar to Scirpus congdonii and was described from herbarium specimens once mislabeled as such. It is a perennial herb forming a clump of erect stems growing up to a meter tall, solitary stems sometimes occurring as well. The stems are three-angled and narrow at the middle. Sheathing leaves occur at the stem bases as well as higher up the stems. The inflorescence occurs at the end of the stem, with small additional ones growing from the uppermost leaf axial. The inflorescence consists of several clusters of many spikelets wrapped at the bases in a leaflike bract.

Scirpus diffusus là loài thực vật có hoa trong họ Cói. Loài này được Schuyler miêu tả khoa học đầu tiên năm 1966.