21. Leaf blades at least 2.5 times as long as wide; petioles usually less than 20 



mm. long; mature ocreae at least 1.5 times as long as broad (22) 



22(21). Perianth glandular (23) 



22. Perianth without glands (25) 



23(22). Achenes biconvex, oval in cross section; styles 2; stems stout, usually 

 over 7 mm. in diameter at base 19. P. densiflorum. 



23. Achenes mostly trigonous, triangular in cross section; styles 3; stems less 



than 6 mm. in diameter at base (24) 



24(23). Achenes black, lustrous, smooth; young flower buds white or green- 

 tipped; inflorescence erect 20. P. punctatum. 



24. Achenes black, dull, minutely pitted; young buds pinkish; inflorescence usually 



nodding 21. P. Hydropiper. 



25(22). Achenes trigonous; styles 3 (26) 



25. Achenes lenticular; styles 2 (27) 



26(25). Inflorescences usually less than 4 cm. long, mostly rounded at the apex; 

 marginal cilia of ocreae usually less than 3 mm. long; achene ovoid, 

 longer than wide, lenticular or trigonous 22. P. Persicaria. 



26. Inflorescences usually more than 4 cm. long, tapering to the apex; marginal 



cilia of ocreae usually 3 mm. long or more; achenes trigonous, 

 about as wide as long 23. P. hydropiperoides. 



27(25). Inflorescences usually less than 4 cm. long, mostly rounded at the apex; 

 marginal cilia of ocreae usually less than 3 mm. long; achene 

 lenticular or trigonous; annual 22. P. Persicaria. 



27. Inflorescences usually more than 4 cm. long, tapering to the apex; marginal 



cilia of the ocreae usually 3 mm. long or more; perennial (28) 



28(27). Peduncles and ocreolae strigose or stipitate-glandular; stamens or styles 

 strongly exserted from the flowers; perianth in fruit 4 mm. long or 

 more, pinkish-red; inflorescence terminal 15. P. amphihium. 



28. Peduncles and ocreolae not strigose nor stipitate-glandular (glands, if present, 



sessile); stamens and styles mostly included; perianth in fruit less 

 than 3.5 mm. long, white or pinkish-white; inflorescences numerous, 

 terminal and lateral 19. P. densiflorum. 



1. Polygonum virginianum L. Jump seed. Fig. 403. 



Annual herb; stems erect or reclining, 3-15 dm. tall; ocreae marginally trun- 

 cate and ciliate; leaf blades ovate to elliptic-ovate or ovate-lanceolate, 3-16 cm. 

 long, acute; flowers in long terminal very loose and interrupted wandlike or spike- 

 hke aggregations; pedicels about 3 mm. long; calyx greenish-white, about 4 mm. 

 long, 4-parted to near the middle; achene lenticular, strongly biconvex, 3.5-4 mm. 

 long, ovoid-oblong, topped by the 2 persistent deflexed and hooked (hornlike) 

 rather rigid styles about 4 mm. long. Antenoron virginianum (L.) Roberty & 

 Vautier, Tovara virginiana (L.) Raf. 



In water or in seepage along streams and about lakes, in low rich woodlands, 

 in e., s.e. and n.-cen. Tex. and Okla. (Ottawa, Muskogee, Pittsburg, Kay, Cherokee 

 and Choctaw cos.), June-Oct.; Que., Ont. and most of e. U.S.; also Pue. and 

 Hgo. 



2. Polygonum sagittatum L. Tearthumb, arrow-vine. Fig. 404. 



Basally stoloniferous or subrhizomatous, probably perennial; stems ascending, 

 thin, weak and reclining or scandent, to 2 m. long, 4-angled and finely channeled, 

 armed on the angles with minute recurved prickles; leaf blades lanceolate or 

 broadly so, 1-12 cm. long, sagittate-cordate basally, apically acute; petioles long 

 in lower leaves, short in upper ones; inflorescences terminal and axillary (a very 



810 



