230 MISC. PUBLICATION 42 3, U. S. DEPT. OF AGRICULTURE 



perianth small, calyxlike; petals none; stamens commonly 4, opposite 

 the perianth segments; ovary 1-celled; fruit an achene. 



Key to the genera 



1. Sepals of the pistillate flowers separate or nearly so, in pairs, the outer ones 

 much smaller, the inner ones enveloping the achene; plants armed with 



stinging bristlelike hairs ; leaves opposite 1. Urtic a. 



1. Sepals of the pistillate flowers united much of their length in a tubular or bell- 

 shaped, 4-lobed calyx; plants without stinging hairs; leaves alternate. 



2. Parietaria 

 1. URTIC A. Nettle 



Stems tall; leaves opposite, with stipules; herbage more or less 

 canescent or tomentose, usually also hispid with stinging hairs; 

 inflorescences elongate, spikelike; stigma sessile or nearly so; achene 

 compressed. 



All of the species flower in Arizona in summer (July to September). 

 Contact with nettles is very irritating to the skin, owing to the formic 

 acid released by the stinging hairs. 



Key to the species 



1. Petioles of the lower leaves more than half as long as to longer than the blades, 



the latter broadly ovate (at least the lower ones), often nearly as wide as 



long, cordate to subcuneate at base, the marginal teeth broadly triangular 



ovate, obtuse or acutish, directed only slightly upward- 1. U. gracilenta. 



1. Petioles mostly much less than half as long as the blades, the latter commonly 



lanceolate and much longer than wide, rounded to cuneate (exceptionally 



cordate) at base, the marginal teeth triangular, very acute, directed strongly 



upward (2). 



2. Stipules linear or narrowly lanceolate, acuminate; herbage green, sparsely 



to copiously (but not densely) pubescent as well as hispid. 



2. U. GRACILIS. 



2. Stipules oblong or broadly lanceolate, obtuse or acutish; stem and the lower 



surface of the leaf blades usually densely grayish pubescent as well as 



hispid 3. U. holosericea. 



1. Urtica gracilenta Greene, Torrey Bot. Club. Bui. 8: 122. 1881. 

 Sierra Ancha (Gila County), Chiricahua and Huachuca Mountains 



(Cochise County), Baboquivari Mountains (Pima County), 4,000 to 

 8,000 feet. New Mexico and Arizona. 



The leaves are bright green on both surfaces and the shorter hairs 

 are sometimes spreading and straight, sometimes subappressed and 

 curly. 



2. Urtica gracilis Ait,, Hort. Kew. 3: 341. 1789. 



Carrizo, Lukachukai, and White Mountains (Apache County), 

 Pinal eno Mountains (Graham County), Chiricahua Mountains 

 (Cochise County), up to 9,000 feet, in springy places and along 

 streams. Almost throughout temperate North America, 



3. Urtica holosericea Nutt., Acad. Nat. Sci. Phila. Jour. ser. 2, 1: 



183. 1847. 



Kaibab Plateau and Grand Canyon (Coconino County), about 7,500 

 feet. Washington to California and Arizona. 



This form apparently intergrades with U. gracilis and is perhaps 

 best regarded as a variety (U. gracilis var. holosericea Jepson). 



