1. Cladium jamaicense Crantz. Saw-grass. Fig. 239. 



Coarse erect reed 1-2.5 m. tall, with short rhizomes; leaves long, very tough, 

 channeled ventrally, with dangerous saw-toothed cutting margins; inflorescences 

 ample, 2-5 dm. long, much-branched, often droopy; spikelets ovoid, chestnut- 

 brown, 3-5 mm. long, in fascicles of 2 to 6 at ends of the branchlets, each with a 

 single fertile floret and below it 2 or 3 other spirally imbricate scales, all but the 

 lowest enclosing stamens; perianth absent; achene obovoid, apiculate, somewhat 

 lustrous, brownish, the obovoid body 2-2.5 mm. long, the apiculate 0.6-1 mm. 

 long. 



Locally abundant in fresh water on margins of streams, ponds and lakes, mostly 

 in areas of calcareous soil, s.e. Tex., Rio Grande Plains, Edwards Plateau and 

 Trans-Pecos, summer; widespread in Carib. region, n. to Gulf States and Va. The 

 var. chinense (Nees) Koyama occurs in China and Japan. 



Most of the plants of Arizona, Nevada and New Mexico, and some plants of the 

 Edwards Plateau and the Trans-Pecos, Texas, have, on the average, slightly smaller, 

 proportionately shorter and more numerous spikelets and denser inflorescences than 

 the plants described above. These have been segregated as a separate species, C. 

 californicum (Wats.) O'Neill. These differences are not well marked but usually 

 the plants from the above states, California and Coahuila are thought to be C. 

 californicum. 



11. Schoenus L. 



About 100 species, world-wide in distribution. 



1. Schoenus nigricans L. Black sedge. Fig. 240. 



Coarsely tufted perennial; culms slender, wiry, erect, simple, 2-6 dm. long, 

 about 1 mm. thick; leaves basally crowded, the lower sheaths chestnut-black and 

 shiny, the upper blades tough, thin, wiry, involute, shorter than the culms, apically 

 spinose; bracts 1 or 2, the lower one far-surpassing the inflorescence, involute and 

 wiry like the leaves; inflorescence a single sessile glomerule of about 10 sessile 

 spikelets; spikelets laterally compressed, of about 5 to 10 distichous much-overlap- 

 ping dark-chestnut to blackish scales of which only the upper few produce mature 

 fruit; perianth bristles few, much shorter than the achene, minutely plumose at the 

 very base; style 3-branched; achene shortly obovoid-trigonous with convex sides, 

 pearly- or bony-white, shiny, jointed abruptly with the difl"erently-textured style 

 which thus does not leave a tubercle. 



Infrequent or rare in creek canyons, about hot springs and other wet places, s. 

 part of Tex. Edwards Plateau, spring; widespread in warm-temp, usually semiarid 

 parts of the world. 



12. Dichromena Michx White-top Sedge 



Tufted or rhizomatous perennials with stems leafy basally, the blades ascending; 

 flowering culms terminating in an involucrate headlike agglomeration of spikelets, 

 the bracts white basally but green distally; spikelets usually whitish; scales several, 

 spirally imbricated or irregularly distichous, the terminal ones enclosing a fertile 

 floret, the lower ones staminate or empty; perianth absent; achenes lenticular, 

 transversely rugose, crowned with the broad persistent base of the style (tubercle) 

 as in Rhynchos-pora. Some authors would include Dichromena within Rhyncho- 

 spora. 



One of the more easily recognizable of the sedges because of the white bases of 

 the bracts; these apparently function to attract insects. Most sedges, on the con- 

 trary, are thought to be wind-pollinated. About 60 species in the Western Hemi- 

 sphere. 



464 



