to a single fertile scale plus one or more sterile scales above, when several scales 

 present the spikelet usually discernibly laterally compressed (i.e., as if the 2 margins 

 of the folded scale were pushed toward each other and the scale creased at the 

 usually keel-like median portion, the breadth of the spikelets then measured from 

 keel to keel of alternating scales and the thickness from side to side of the same 

 folded scale), the spikelet axis either disarticulating at the top of each internode 

 or only at its base or often completely persistent, each internode of the spikelet 

 axis often with 2 thin "wings" on each side of the flower (the decurrent lower 

 margins of the next superjacent scale); scales usually folded, either persistent or 

 deciduous; perianth absent; stamens 1 to 3; styles 2- or 3-branched; achenes 

 lenticular or trigonous, often stipitate and/ or apiculate, jointed with the style 

 usually at the very top of the achene, the achenial body there with or without a 

 minute apiculus but the latter (if present) of the same color and texture as the 

 main part of the achene. 



With upwards of 900 species in warm regions, Cyperus, a vast, difficult genus, 

 is often made more confusing by a very unsatisfactory and arbitrary segregation 

 of smaller "genera," such as Mariscus Vahl, Pycreus Beauv., Kyllinga Rottb. 



1. Achene lenticular, biconvex or concavo-convex (2) 



1. Achene trigonous or vaguely so, occasionally appearing nearly terete but 



definitely not biconvex nor concavo-convex (9) 



2(1). Achene dorsiventrally compressed, i.e., with one of the sides appressed to 

 the spikelet axis, the other appressed to the inner surface of the 

 scale, the latter not keeled 1. C laevigatus. 



2. Achene laterally compressed, i.e., with one angle next to the spikelet axis and 



the 2 slightly convex sides parallel with the 2 sides of the scale, the 

 scale being folded and creased at the keel-like median (3) 



3(2). Each spikelet with only 2 scales and only one achene (4) 



3. Each spikelet with 6 to 60 scales, usually several of them fertile (6) 



4(3). Stamens solitary; plants rhizomatous, the culms rising at intervals of 3-10 

 mm 2. C. brevifolius 



4. Stamens paired; culms densely tufted or plants mat-forming (5) 



5(4). Densely tufted with a culm density of 4 to 20 per square cm. in the tufts; 

 culms about 0.7 mm. thick basally; inflorescence 3-8 mm. long; 

 bracts with translucent corners at the very base; spikelets 2-2.5 mm. 

 long, 0.7-0.8 mm. broad, sordid-whitish or very pale-brownish; 

 lower (fertile) scale 1.7-2.4 mm. long; achene elliptic, 0.9-1.1 mm. 

 long (not including the apiculus), 0.5-0.6 mm. broad, ripening to 

 a very dark brown 3 C. tenuifoliits. 



5. Culm density in the mat 1 to 4 per square cm.; culms 0.8-1.8 mm. thick 



basally; inflorescence 7-14 mm. long; bracts without translucent 

 corners; spikelets 2.3-3 mm. long, 1.2-1.3 mm. broad, buffy-white 

 to white; lower (fertile) scale 2.2-2.9 mm. long; achene obovate, 

 1-1.4 mm. long (not including the apiculus), 0.75-0.9 mm. broad, 

 ripening black 4. C. sesquiflorus. 



6(3). Spikelets borne in lax spikes 12-40 mm. long and 12-23 mm. thick; scales 

 with broad white-hyaline margins markedly contrasting with the 

 brownish sides; achenes 1.2-1.5 mm. long 5. C. alhomarginatiis. 



6. Spikelets borne in heads or glomerules; scales with thin but not hyaline nor 



white margins; achenes mostly less than 1.2 mm. long (7) 



7(6). The lower part of the edges of the internodal niches of the spikelet axis 

 with minute persistent wings which become narrowed and join 



abaxlally forming a minute cup at the base of the achene 



6. C. polystachyos. 



416 



