124 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM, 
40. Carex hystricina Muhl.; Willd. Sp. Pl. 4: 282. 1805. 
Type Locauity: ‘‘Habitat in humidis Pennsylvaniae.”’ 
RanGE: British America to Georgia, Nebraska, and New Mexico. 
New Mexico: North Percha Creek ( Metcalfe 1122). 
41. Carex rostrata Stokes in With. Bot. Arr. Veg. Brit. ed. 2. 2: 1059. 1787. 
Type Locatity: ‘‘ Bogs of Isla, and on Bentelkerny and Breadalbane,’’ England. 
RanGE: British America to California, New Mexico, and New York; also in Europe. 
New Mexico: Truchas Peak; Silver Spring Canyon; Chama. Bogs, Transition to 
Arctic-Alpine Zone. 
9. KOBRESIA Wip. 
Slender tufted perennial with erect culms and solitary spikes; spikelets 1 or 
2-flowered, spicate; perigynium none; stigmas 3; achenes obtusely 3-angled, sessile. 
1. Kobresia bellardi (All.) Degland in Loisel. Fl. Gall. 2: 626. 1807. 
Carex bellardi All. Fl. Pedem. 2: 264. pl. 92. f. 2. 1785. 
Kobresia scirpina Willd. Sp. Pl. 4: 205. 1805. 
Elyna spicata Schrad. Fl. Germ. 1: 155. 1806. 
Elyna bellardi Koch, Linnaea 21: 616. 1848. 
TYPE LocaLity: European. 
Rance: Arctic America, south in the Rocky Mountains to northern New Mexico; 
also in Europe and Asia. 
New Mexico: Costilla Valley (Wooton). Wet ground. 
Order 11, ARALES. 
15. LEMNACEAE. Duckweed Family. 
Small unattached aquatics, the plant body a thallus, rooting from beneath. 
KEY TO THE GENERA. 
Roots several from a prominently nerved thallus............ 1. SprropELa (p. 124). 
Root solitary from a faintly nerved thallus...........-...-. 2. Lemna (p. 142). 
1. SPIRODELA ScuHLED. 
Thallus disk-shaped, 7 to 12-nerved, 2 to 10 mm. long, bearing a single cluster of 
4 to 16 elongated roots; spathe saclike; ovary 2-ovuled; fruit unknown. 
1. Spirodela polyrhiza (L.) Schleid. Linnaea 13: 392. 1839. 
Lemna polyrhiza L. Sp. Pl. 970. 1753. 
Tyre Locauity: ‘‘Habitat in Europae paludibus fossis.”’ 
RanaeE: In still water throughout most of North America and in the Old World. 
Reported by Mr. J. R. Watson from ‘‘ponds about the fair grounds, Albuquerque.’’? 
2. LEMNA L. Dvuckweep. 
Thallus disk-shaped, usually provided with a central nerve, with or without lateral 
ones, each with a single root; ovary with 1 to 6 ovules; fruit ovoid, more or less ribbed. 
KEY TO THE SPECIES, 
Fronds long-stipitate, narrowly oblong, 6 to 10 mm. long, mostly sub- 
merged, often forming large masses............-.200--0 eee ee eee 1. Z. trisulea. 
Fronds not stipitate, broadly elliptic to obovate, 3 mm. long or less, 
floating. . 
Fronds obovate, 3 mm. long; fruit more or less lenticular....-..-. 2. L. minor. 
Fronds elliptic or oblong, 2 mm. long or less; fruit elongated...... 3. L, minima, 
1 Bull. Univ. N. Mex. 49: 94. 1908. 
