144 URTICACEAE (nettle FAMILY) 



bricated bracts, each 2-flowered. Achene invested with the enlarged scale-like 

 calyx. 



1^ Humulus lupulus L. Sp. PI. 1028. 1753. Leaves commonly longer than 

 the petioles: the fruiting calyx, achene, etc., sprinkled with yellow resinous 

 grains, giving the bitterness and aroma of the hop. — In the mountains from 

 New Mexico to British America and eastward across the continent. 



la. Humulus lupulus neomexicanus Nels. & Ckll. Proc. Biol. Soc. Wash. 

 16: 45. 1903. Leaves divided or sometimes parted, the segments varying 

 from broadly lanceolate to nearly linear, acuminate, freely sprinkled with 

 resin particles on the lower face: fruiting bracts ovate-lanceolate, usually 

 acuminate, finely pubescent. — ^This is the common form in Colorado and New 

 Mexico. 



33. URTICACEAE Reichenb. Nettle Family 



Herbs with simple alternate or opposite leaves, and small greenish apetalous, 

 monoecious, dioecious, or polygamous flowers variously clustered. Calyx 2-5 

 cleft, or of distinct sepals. Stamens as many as the lobes of the calyx and 

 opposite them; filaments wrinkled and inflexed in the bud. Stigma simple, 

 peniciUate or filiform; ovary always 1-celled and 1-ovuled, becoming an 

 achene. — Ulmaceae in part. 



Leaves alternate: no stinging hairs 1. Parietaria. 



Leaves opposite; beset witli stinging hairs . 2. Urtica. 



1. PARIETARIA L. 



Annual herbs without stinging hairs. Leaves alternate, 3-nerved, petioled 

 and without stipules. Flowers axillary, polygamous, and glomerate in a 

 leafy involucre. Calyx of the staminate flowers 4-parted; the fertile tubular 

 or campanulate (4-lobed), and permanently inclosing the ovary. Stigma 

 peniciUate. 



1. Parietaria pennsylvanica Muhl. Willd. Sp. PI. 4: 955. 1806. Low, sim- 

 ple or sparingly branched, minutely downy: leaves oblong-lanceolate, thin, 

 veiny, roughish with opaque dots: flowers shorter than the leaves of the in- 

 volucre. — From Colorado to Wyoming; across the continent. 



2. URTICA L. Nettle 



Perennial herbs armed with stinging hairs, with distinct stipules, monoe- 

 cious (rarely dioecious) greenish clustered flowers, mostly in racemes or spikes 

 or loose heads. Sterile flowers with four stamens inserted around the cup- 

 shaped rudiment of a pistil. Fertile flowers with the 2 outer sepals smaller. 

 Stigmas sessile. Achene flattened and ovate. 



Leaves broadly dvate; cordate , . . , ~i^ , . . 1. U, dioiea. 



Leaves ovate-lanceolate, base rounded or barely subcordate. * 



Tomentose beneath 2. U. holosericea, 



Glabrate or slightly pubescent and hispid '3. U. gracilis. 



1. Urtica dioiea L. Sp. PI. 984. 1753. A coarse weedy perennial 5-15 dm. 

 high, very bristly and stinging: leaves ovate, cordate, acute, deeply serrate, 

 downy beneath as is also the upper part of the stem: spikes much branched. — 

 Naturalized from Europe and now widely .distributed in the United States, 

 mostly in waste grounds. 



2. Urtica holosericea Nutt. Journ. Acad. Phila. N. S. 1: 183. 1847. Tall 

 and stout, more or less bristly, finely and densely tomentose especially on the 

 lower side of the leaves: leaves thick, oblong to ovate-lanceolate, rounded at 

 base, on short stout petioles: staminate flowers in loose slender diffuse panicles 



