190 CYPERACEAE 



14. DICHROMENA Michx. 



Leafy -stemmed sedges, perennial by rootstocks, the spikelets crowded in a terminal 

 head involucrate by several bracts, which are often white at the base. Spikelets compressed, 

 several-many-flowered. Scales spirally imbricated all around, several of them with imper- 

 fect flowers, or empty. Perianth none. Stamens 3. Style subulate. Stigmas 2, very 

 slender. Achene lenticular, transversely rugose, crowned with the broad persistent base 

 of the style (tubercle). The plants bloom from spring to fall. WHITE-TOP. 

 Involucre of 2 bracts : achenes barely 1 mm. long. 1. D. nivea. 



Involucre of 4-10 bracts : achenes over 1 mm. long. 



Bracts of the involucre 4-6, linear: tubercle truncate on top of the achene. 



Leaves filiform above the dilated base : achenes dark ; tubercle low, blunt. 2. D. Floridensis. 

 Leaves linear above the dilated base : achenes pale ; tubercle long, acute. 3. D. colorata. 



Bracts of the involucre 7-10, lanceolate : tubercle decurrent on the sides of the 



achene. 4. D. lattfolia. 



1. Dichromena nivea Boeckl. Stems tufted, 1-3 dm. tall, very slender nearly terete, 

 smooth : leaves mostly shorter than the stems ; blades very narrowly linear or linear-fili- 

 form : bracts of the involucre 2, very unequal, slender beyond the white dilated bases : 

 head less than 1 cm. in diameter, pearly white, erect : spikelets ovate, 3-4 mm. long, 

 crowded : scales smooth, notched at the apex, closely imbricated : achenes lenticular, 

 plump, obovoid, barely 1 mm. long, short-beaked, with prominently wrinkled sides. 



In wet soil and low grounds, Arkansas and Texas. 



2. Dichromena Floride'nsis Britton. Stems copiously tufted, 2-4 dm. tall, smooth, 

 slender : leaves numerous ; blades involute-filiform, smooth : bracts of the involucre 4-6, 

 slenderly attenuate : heads about 1 cm. in diameter : spikelets oblong : scales pale : achenes 

 obovoid, slightly over 1 mm. long, dark brown, finely wrinkled, the tubercle nearly trun- 

 cate on the top of the achene-body. 



In low pine lands, southern Florida. 



3. Dichromena colorata (L.) A. S. Hitchcock. Stem slender, rather sharply tri- 

 angular, 3-6 dm. tall. Leaf-blades narrowly linear, much shorter than the stem : bracts 

 of the involucre 4-6, reflexed when mature, yellowish white at the base : head globose, 

 1-2 cm. in diameter : spikelets narrowly oblong, acute : scales membranous, lanceolate, 

 nearly white, 1 -nerved, subacute : achenes obovoid, a little over 1 mm. long, excluding 

 the tubercle, pale brown, compressed, nearly truncate at the summity there covered by the 

 tubercle which is not decurrent on its edges. [D. leucocephala Michx.] 



In moist sandy soil, pine lands, New Jersey to Florida and Texas. Also in tropical America. 



4. Dichromena latif olia Baldw. Similar to the next preceding species but the stem 

 stouter, obtusely triangular or nearly terete. Leaf -blades lanceolate or linear-lanceolate, 

 tapering gradually to a long acuminate apex from a broad base, 3-8 mm. wide, sometimes 

 overtopping the stem, but the lowest much shorter : bracts of the involucre 7-10, strongly 

 reflexed when old : head globose, 1-2 cm. in diameter : spikelets oblong, subacute : scales 

 ovate-lanceolate, nearly white, rather obtuse : achenes nearly orbicular in outline, a little 

 over 1 mm. long, excluding the tubercle, pale brown, faintly wrinkled transversely and 

 longitudinally so as to appear reticulated ; the tubercle decurrent on its margins. 



In wet pine lands, Virginia to Florida and Texas. 



15. ABILDGAARDIA Vahl. 



Perennial, or sometimes annual, acaulescent herbs. Leaves basal : blades narrow, 

 commonly involute : scapes tufted, jointless, simple. Involucre of a single small bract. 

 Spikelets solitary or several in terminal umbels or clusters, several to many-flowered : 

 scales imbricated in 2 rows, or in 3 rows by the twisting of the rachis, keeled, decurrent, 

 deciduous. Perianth wanting. Stamens. 1-3. Style pubescent, with a swollen base, de- 

 ciduous. Stigmas 3. Achenes 3-angled, broadest above the middle, warty, pale. 



1. Abildgaardia monostachya (L.) Vahl. Perennial, glabrous. Leaves firm, 

 shorter than the scape ; blades nearly filiform above the discolored bases, slightly involute, 

 sharp-pointed : scapes tufted, very slender or filiform, 1-4 dm. tall, erect, smooth : bracts 

 of the involucre much shorter than the spikelets, inconspicuous : spikelet solitary or some- 

 times 2 together, flattened, ovoid or conic, 1-1.5 cm. long, pale : scales in 2 rows, acute or 

 mucronulate, with broad white margins : stigmas 3 : achenes slightly pear-shaped, 2-2.5 

 mm. long, constricted near the base, copiously warty, yellowish white, often apiculate. 



In sandy or rocky soil, peninsular Florida and the Keys. Also in the tropics. Spring to fall. 



16. SCHOENUS L. 



Perennial rush-like herbs, with tufted rigid scapes. Leaves basal ; sheath dark -col- 



