APETALOUS EXOGENOUS PLANTS. 491 



ovary ; calyx of the fertile flower 4-sepalons, unequal, the 

 inner ones dilated in fruit, and inclosing the achenium ; 

 stigma sessile, tufted ; achenium straight, ovate, smooth, 

 compressed. — Herhs, with stinging hairs, opposite leaves, 

 and greenish /oz6'cr5, in panicled spikes or close clusters. 



♦ Flowers in panicled or simple spikes. 



U. GRACILIS, Ait. Stem tall, 4-angled, smoothish, slen- 

 der; leaves long-petioled, ovate-lanceolate, coarsely serrate, 

 acute, rounded at the base, 3-5-nerved, smoothish, the 

 petioles bristly; spikes very slender, loosely panicled. 

 (U. procera, Willd.) Low ground in the upper districts, 

 and northward. July and August. Stem 3°-4° high, 

 mostly simple; leaves thin, 4'-6' long. Perennial. 



U. DioiCA, L. Hispid throughout; stem 4-angled, pu- 

 bescent above, branching ; leaves rather short-petioled, 

 ovate, cordate, acuminate, coarsely serrate, pubescent be- 

 neath ; spikes much branched; floivers often dioecious. 

 Waste places. Introduced. June-August. Stem 2°-3° 

 high ; leaves 3-4' long, thicker than in the preceding and 

 flowers larger. Perennial. 



U. CAPiTATA, Willd. Stem 4-angled, roughish ; leaves 

 large, long-petioled, rough, oblong-ovate, slightly cordate, 

 coarsely serrate, 3-nerved, those on the branches alternate; 

 sjjike solitary, leafy at the summit. Wet shaded places. 

 July and August. Stem 3°-5° high. 



** Flowers in simple clusters shorter than the petioles. 



U. UREXS, L. Stem 4-angled, hairy; leaves ovate, 

 coarsely serrate, 5-nerved, hairy ; clusters by pairs in each 

 axil, loose, peduncled. Damp soil. December-February. 

 Stem 1° high. Annual. 



U. CHAMiEDRYOiDES, Pursli. Stem smooth ; leaves 

 small, nearly sessile, ovate, coarsely serrate, hairy beneath, 

 hairy and bristly above ; clusters nearly sessile, globose, 

 dense; calyx hairy. February and March. Stem 4'-6' 

 high. 



