LEMNACEAE (DUCKWEED FAMILY) 105 



C.f estiva in the presence of elongated bracts which are expanded and strongly 

 nerved at the base, the two or three lower much exceeding the mostly paler 

 head: lowest spike rarely distinct. Common throughout our range. 



(- - Spikes mostly separated, or if aggregated the individual spike well defined. 



M- Perigyniwn thin and scale-like, with little distinction between the margin and 

 the body, mostly greenish. 



68. Carex scoparia Schk. Riedgr. Nachtr. 20. f. 175. 1806. Culms slender, 

 erect, roughish above, 1.5-7.5 dm. tall: leaves less than 3 mm. wide: spikes 

 3-10, oblong, narrowed at both ends, bright brown, 6-16 mm. long, usually 

 aggregated into an ovoid head: perigynia lanceolate, 4-6 mm. long, rather less 

 than 2 mm. wide, narrowly wing-margined, several-nerved on both faces, 

 tapering into the ciliate two-toothed beak: scales thin, brown, acuminate or 

 cuspidate, shorter than the perigynia. Extending into Colorado from the 

 eastern States. 



M- *-+ Perigynium thickened in the middle, with conspicuous wing-margins 

 which are more or less incurved, mostly tawny or brown. 



69. Carex petasata Dew. Am. Journ. Sci. 29: 246. 1836. Caespitose: culm 

 erect, 1-4 dm. high, scabrous above, mostly longer than the leaves: spikes 3-6, 

 erect, ovoid, all contiguous into an oblong dark brown head: lower bracts often 

 green and as long as the head, but usually all scale-like: perigynium ovate or 

 ovate-lanceolate, broadly winged, nerved, rough on the margins, contracted 

 into a beak scarcely as long as the body, the whole not longer than the thin- 

 margined scale. C. leporina. Frequent in our range. 



70. Carex Liddonii Boott, Hook. Fl. Bor. Am. 2: 214. 1840. Culm erect or 

 nearly so: spikes 3-6, ovoid or oblong, pointed, erect, chaffy at the base, con- 

 spicuously fulvous in color, contiguous, or loosely aggregated into an oblong 

 head 2-3 cm. long: perigynium large and conspicuous, greenish or tawny, firm 

 in texture, lanceolate, 8-12 mm. long, thrice as long as the elliptic brown 

 achenium, few-nerved when mature, rough on the narrowly winged and in- 

 curved margins, very gradually beaked, about the length of the acute and 

 thin-margined scale. C. adusta congesta VV. Boott. Mostly at high altitudes; 

 Colorado to Montana; said to occur in Arizona. 



71. Carex festucacea Willd. Sp. PI. 4: 212. 1805. Culms nearly or quite 

 smooth, erect, 3-10 dm. tall: leaves erect, 2-4 mm. wide, shorter than the 

 culm: spikes 3-8, green-brown, oblong or nearly globular, clustered, 4-8 mm. 

 in diameter: perigynia orbicular or very broadly ovate, broadly wing-margined, 

 about 3 mm. irr diameter, several-nerved on both faces, the roughish beak 

 about one third the length of the body: scales acute or obtusish. C. straminea. 

 On the plains at the eastern base of the Rocky Mountains. 



72. Carex praticola Rydb. Mem. N. Y. Bot. Card. 1: 84. 1900. Culm 

 very slender towards the top, weak and nodding at maturity, erect when 

 young: leaves narrow, very long-pointed: spikes all silvery-brown, long atten- 

 uated at the base, the lower rather remote: perigynium thin and papery, ovate- 

 lanceolate, nearly nerveless. C. adusta minor; C. pratensis Drej. Colorado 

 and into British America. 



The following have also been reported from this range but probably some of 

 the specimens so reported are referable to other species: C. magellanica Lam.; 

 C. viridula Michx.; <". retrorsa Schkur.; C. microglochin Wahl. 



18. LEMNACEAE Dumort. DUCKWEED FAMILY 



Minute aquatic plants without stems or leaves, but a flat or disk-like irregular 

 plant-body which may be called the thallus or frond. These float on or near 

 the surface and increase vegetatively by lateral growth and branching, the 

 branches being lightly connected by slender stalks which soon allow them to 



