180 Karl M. Wiegand and Arthur J. Eames 



35. URTICACEAE (Nettle Family) 



a. Plant arborescent; ovule suspended. 



b. Flowers from special buds on wood of the preceding year, developing before 



the leaves ; stamens erect in the bud ; anthers extrorse ; leaves serrate ; fruit a 



flat samara. 1. Ulmus 



b. Flowers on shoots of the season, developing mostly with the leaves ; anthers 



introrse; fruit fleshy. 



c. Flowers racemose, or the pistillate ones mostly solitary ; stamens erect in the 



bud; leaves serrate. 2. Celtis 



c. Flowers, at least the pistillate ones, densely spicate or capitate ; stamens 

 inflexed in the bud. 

 d. Leaves entire, pinnately veined ; staminate flowers in globose racemes. 



3. Maclura 

 d. Leaves dentate, often lobed, palmately veined; staminate flowers spicate. 



4. Morus 

 a. Plant herbaceous ; ovule suspended or erect. 



b. Leaves palmately 3-7-lobed or -divided ; stamens erect in the bud ; ovule sus- 

 pended. 

 c. Leaves 5-7-divided, the divisions narrow ; pistillate flowers forming an irregular 



spicate cluster ; plant erect. 5. Cannabis 



c. Leaves 3-5-lobed, the divisions broad; pistillate flowers in definitely organized 

 cone-like spikes ; plant twining. 6. Humulus 



b. Leaves not lobed ; stamens inflexed in the bud ; ovule erect ; plant erect. 

 c. Calyx of the pistillate flowers of 2-5 separate or nearly separate sepals. 



d. Leaves alternate, with stinging hairs; sepals of the staminate flowers 5, of 



the pistillate flowers 4 ; stigma long-subulate ; achenes oblique, reflexed, 



naked. 7. Laportea 



d. Leaves opposite; sepals of the staminate and the pistillate flowers both 3-4; 



stigma capitate-tufted.. 



e. Plants with stinging hairs ; achenes inclosed by the two inner and larger 



sepals; stems opaque. 8. Urtica 



e. Plants without stinging hairs, glabrous ; achenes naked or nearly so ; 

 stems translucent. - 9. Pilea 



c. Calyx of the pistillate flowers tubular or cup-shaped, 2— 4-lobed, inclosing the 

 achene ; plant unarmed. 

 d. Leaves opposite, serrate ; flowers glomerate, in interrupted axillary spikes 

 which are sometimes leafy at the top, not involucrate ; stigma long, 

 filiform. 10. Boehmeria 



d. Leaves alternate, entire ; flowers in short axillary glomerules, involucrate ; 

 stigma tufted. 11. Parietaria 



1. Ulmus (Tourn.) L. 



a. Flowers slender-pedicelled, clustered or racemose, drooping ; leaves smooth, or some- 

 what rough above ; bud scales dark-margined. 

 b. Flowers subumbellate or corymbose ; fruit notched at least halfway to the seed ; 

 branches not corky-winged ; buds glabrous ; petioles 5-10 mm. long ; leaf blade 

 elliptic-ovate, very oblique at base. 1. U. americana 



b. Flowers racemose ; fruit with a shallow notch ; branches often corky-winged ; 

 buds pubescent; petioles 2-5 (8) mm. long; leaf blade elliptic-obovate, usually 

 slightly oblique at base. 2. U. raccmosa 



a. Flowers short-pedicelled, in dense capitate clusters, not drooping; leaves scabrous, 

 or rarely smooth above; bud scales uniformly dark. 

 /». Seed near the center of the large (17 mm. wide), shallowly notched, oval wing; 

 leaf blade large, 8-18 cm. long; stamens 5-9; twigs rather stout; buds large. 

 c. Twigs of the preceding season pale brown, scabrous-papillose ; bud scales 



