164 CYPERACEAE 
b. Wings of the rachis separating from it as interior scales: annuals. 
Spikes loose, or if dense not narrowly cylindric : spikelets 6-25 mm. long. 
Spikelets crowded : scales loose. 39. C. erythrorhizos. 
Spikelets not crowded: scales closely appressed. 40. C. digitalus. 
Spikes very dense, cylindric: spikelets 3-5 mm. long. 41. C. Halei. 
B. Rachis of the spikelets deciduous. 
Rachis breaking up into 1-fruited joints: spikelets nearly terete. 
Spikes solitary : scapes filiform: plants perennial. 42. C. Floridanus. 
Spikes umbellate or capitate-congested: scapes stout to slender: 
plants annual. 
Scales of the spikelets distant: achene linear-oblong. 43. C. Engelmannii. 
Scales of the spikelets manifestly imbricated : achene obovoid. 
Spikelets relatively loosely spicate. : 
Spikes dull brown: scales thin, not tightly appressed. 44. C. speciosus. 
Spikes yellowish or grayish brown : scales firm, appressed. 45. C. ferax. 
Spikelets densely congested into 1-4 heads. 
Inflorescence umbellate: spikes disposed at the ends of the 2-4 
rays of theumbel. | : 46. C. Eggersii. 
Inflorescence capitate: spikes collected into a terminal con- 
gested cluster. 47. C. oxycarioides. 
Rachis deciduous above the lower pairof scales: plants perennial by hard 
corm-like tubers. 
Achene narrowly linear-oblong, 212-4 times as long as thick. 
Spikelets distinctly flattened, several-many-flowered. 
Spikelets in dense globular heads. 48. C. Martindalet. 
Spikelets loosely spicate or relatively so. 
Spikelets chestnut-brown. 49. C. setigerus. 
Spikelets yellow to yellow-brown. 
Seales appressed. 50. C. strigosus. 
Seales loose, somewhat spreading. 51. C. stenolepis. 
Spikelets nearly terete to a little flattened, 1-few-flowered. 
Spikelets loosely spicate. 
Spikelets 1-2 cm. long: achene about 3 mm. long. 52. C. refractus. 
Spikelets less than 1 em. long: achene 1.5 mm. long. 53. C. dissitiflorus. 
Spikelets capitate or capitate-spicate. 
Spikelets all reflexed : scapes almost always rough. 94. C. retrofractus. 
Spikelets spreading or only the lower ones reflexed : scapes 
smooth. 
Spikes or heads dense, cylindrie to globose. 
Spikes globose. 55. C. ovularis. 
Spikes cylindric to oval or obovoid. 
Spikelets 3-7 mm. long: spikes obovoid or cylindric. 
Spikes obovoid: lower spikelets reflexed. 56. C. retrorsus. 
Spikes cylindric. 
Spikes 0.5-2 em. long, simple. 
Spikelets 3-4 mm. long, 1-2-flowered. 57. C. cylindricus. 
Spikelets 5-7 mm. long. 3-4-flowered. 58. C. Plankii. 
Spikes 1.5-3.5 cm. long, usually compound. 59. C. cylindrostachys. 
Spikelets 8-10 mm. long: spikes oval. 60. C. Lancastriensis. 
Spikelets loosely spicate or capitate. 
Spikelets 8-12 mm. long, subulate. 61. C. uniflorus. 
Spikelets 3-5 mm. long, not subulate. 62. C. subuniflorus. 
Achene oblong to obovoid, not more than twice as long as thick. 
Spikelets with 1-4 achenes. 
Rachis wingless or narrowly winged. 
Umbelsimpleor head solitary : leaf-bladesrelatively narrow. 
Spikelets loosely spicate. 
Spikelets densely spicate or capitate. 
B 
. C. tetragonus. 
Heads ovoid to cylindric. 64. C. flavus. 
Heads globose to subglobose. 
Heads dark brown: scales mucronulate. 65. C. fuligineus. 
Heads green or greenish brown: scales not mu- 
eronulate. 
Achene 2 mm. long : scales about 2 mm. long. 66. C. filiculmis. 
Achene 1 mm. long: scales less than 2 mm. 
long. 67. C. Blodgettii. 
Umbel compound : leaf-blades relatively broad. 68. C. ligularis. 
Rachis-wings broad, membranous. 
Scales firm, not appressed. 69. C. Grayi. 
Scales thin, closely appressed. 70. C. echinatus. 
Spikelets with 5-10 achenes. 
Heads sessile, or on rays less than 2 cm. long. "1. C. brunneus. 
Heads terminating rays 2-7 em. long. 72. C. Ottonis. 
1. Cyperus flavéscens L. Annual, yellowish green. Leaf-blades 2-3 mm. wide, 
smooth, the longer usually exceeding the inflorescence: scapes very slender, tufted, 7-30 
cm. tall: spikelets in 3's-6's, linear, subacute, yellow, many-flowered, flat, 8-18 mm. long, 
3-4 mm. broad ; the clusters terminal and sessile, or on 1-4 short rays: scales ovate, ob- 
tuse, 1-nerved, appressed, twice as long as the achene: stigmas 2: achenes orbicular-obo- 
void, black, obtuse, shining, the superficial cells oblong. 
In marshy soil, Maine to Michigan, Florida and Mexico. Alsoin the Old World. Summer and fall. 
2. Cyperus diándrus Torr. Annual, deep green. Leaf-blades about 2 mm. wide: 
scapes tufted, slender, 5-40 cm. tall: bracts of the involucre usually 3: spikelets 8-18 
mm. long, linear-oblong, acute, flat, many-flowered ; the clusters sessile and terminal or at 
