142 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



41. URTICACEAE. Nettle Family. 



Leaves lobed or divided. Plants without stinging hairs. 

 Plants erect annuals; leaves divided to the base into several leaflets. 



1. CANNABIS. 

 Plants twining perennials; leaves toothed or merely lobed, not divided to the base. 



2. HTJMULTTS. 



Leaves merely toothed. 

 Leaves alternate. 

 Plants without stinging hairs; leaves lanceolate, lees than 2.5 cm. wide; flower 



clusters sessile in the axils of the leaves 3. PARIETARIA. 



Plants with stinging hairs; leaves broadly ovate, 5-12 cm. wide or wider; flowers in 



loose branched cymes ... 4. TJRTICASTRUM. 



Leaves opposite. 



Plants with stinging hairs, perennial 5. TTRTICA. 



Plants without stinging hairs, minutely hairy or glabrous. 



Plants annual, glabrous; leaves shining, succulent, the petioles usually as long 



as the blades; flowers in loose cymes 6. PILEA. 



Plants perennial, more or less hairy; leaves not shining, thin, the petioles 

 shorter than the blades; flowers in spikes or loose cymes.. 7. BOEHMERIA. 



1. CANNABIS L. 

 1, Cannabis sativa L. Hemp. 



Occasional in waste ground about Washington. June-Aug. Native of Eurasia; 

 common in cultivation and often escaping. 



2. HUMULUS L. Hop. 

 1. Humulus lupulus L. Common hop. 



Rare as an escape from cultivation. Aug.-Sept. Native of Eur. ; often cultivated in 

 the U. S. for ornament or for its bracts, which are used in making yeast, and frequently 

 escaping; 



Humulus japonicus Sieb. & Zucc, the Japanese hop, was collected in waste ground 

 along the Washington river front, Sept., 1899 (Steele). Native of Japan; often culti- 

 vated for ornament, and escaped at various places in the U. S. 



3. PARIETARIA L. 



1. Parietaria pennsylvanica Muhl. Pelutory. 



Rich woods or along stone walls; rare. June-July. Widely distributed in N. 

 Amer. 



4. URTICASTRUM Fabr. 



1. Urticastrum divaiicatum (L.) Kuntze. Wood nettle. 



Rich woods and alluvial soil; common. July-Oct. Eastern N. Amer. (Laportea 

 canadensis Gaud.) 



5. TTRTICA L. Nettle. 



Leaves lanceolate or ovate-lanceolate, usually twice as long as broad or longer, rounded 

 or cordate at the base, evenly toothed with comparatively small teeth, only 

 slightly bristly beneath 1. TJ. gracilis. 



Leaves ovate or broadly ovate, usually less than twice as long as broad, coarsely and 

 often irregularly toothed, very bristly beneath 2. TJ. dioica. 



1. TJrtica gracilis Ait. 



Wet soil, especially on canal banks, there abundant. June-Aug. Widely dis- 

 tributed in N. Amer. 



2. TJrtica dioica L. 



Moist soil; frequent. May-July. Native of Eur.; naturalized in the eastern U. S. 



