CYPERACEAE. 49 



spike staminate; pistillate spikes 3-8, usually close together, sessile or nearly 

 so, 2-5 cm. long; perigynia thin, much inflated, 8-10 mm. long, ovoid, attenuate 

 into a long beak, strongly nerved, reflexed, much longer than the sharp pointed 

 scales. In wet places. 



66. CYPERUS. 



Annual or perennial; stems simple, triangular, leafy near the 

 base, and with one or more leaves at the summit which form an 

 involucre for the simple or compound umbellate or capitate 

 inflorescence; rays of the umbel sheathed at the base, usually 

 very unequal, one or more of the heads or spikes commonly 

 sessile; spikelets flat or roundish, few to many-flowered; scales 

 concave, 2-ranked, all but the lower one flower-bearing; flowers 

 perfect; perianth none; stamens 1-3; akene lenticular or tri- 

 angular. 



Rachilla of spikelets not winged; annuals. 



Scales with recurved tips. C. aristatus. 



Scales acuminate, without recurved tips. C. acuminatus. 



Rachilla of spikelets winged. 



Wing of rachilla separating in scale-like pieces; annual. C. erythrorhizos. 



Wing of rachilla persistent ; perennials. 



Scales of spikelets deciduous from the rachilla; plant 



stoloniferous and tuberiferous. C. esculentus. 



Scales of spikelets persistent, the whole spikelet 

 breaking away from the axis early; plants with 

 hard corm-like bases. 



Spikelets much flattened; akene narrowly oblong. C. strigostis. 

 Spikelets not much flattened; akenes broadly ob- 



ovoid. C. houghtonii. 



Cyperus aristatus Rottb. Annual, stems 1-15 cm. tall, ascending; leaves 

 flat, about 1 mm. wide, often curved, about equalling the stems; bracts much 

 exceeding the inflorescence; spikelets ovate-lanceolate, 3-5 mm. long, in 

 dense heads, terminating the branches of an unequally rayed umbel, or rarely 

 all aggregated into a single compound head; scales green, becoming brown, 

 all with strongly recurved awn-like tips. Stream banks, common. 



Cyperus acuminatus Torr. & Hook. Much like C. aristatus, usually taller; 

 spikelets pale green, oblong-lanceolate, the scales merely acuminate, the tips 

 but slightly recurved. Banks of Snake River at Almota, rare. 



Cyperus erythrorhizos Muhl. Annual; stems usually 15-60 cm. tall, 

 sometimes much smaller; leaves flat, commonly 2-4 mm. broad, shorter than 

 the stem; involucral leaves 4-8, broad at base, far exceeding the inflorescence; 

 spikelets bright chestnut, linear, 5-6 mm. long, densely crowded into flattened 

 spikes, 1-3 cm. long, the latter umbelled on the unequal branches of the primary 

 umbel; scales oblong, keeled, the green midrib prolonged into a short, mucro- 

 nate tip; wings of the rachis separating to the base, forming pairs of small 

 scales. Banks of Snake River, frequent. 



Cyperus esculentus L. Nut Grass. Perennial, with horizontal tuber- 

 bearing rootstocks; stems 30-60 cm. tall; leaves flat, 4-5 mm. long, exceeding 

 the stem; involucral leaves as long as the others, far exceeding the inflorescence; 

 umbel usually simple or nearly so, the rays very unequal, the spikelets arranged 

 in loose spikes; spikelets linear, diverging, mostly two-ranked, 8-12 mm. long; 



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