188 Karl M. Wiegand and Arthur J. Eames 



2. Polygonum (Tourn.) L. 



a. Stems not twining; leaves linear to ovate, not cordate but sometimes sagittate or 

 hastate. 

 b. Stems not armed with prickles. 

 c. Flowers axillary. 



d. Calyx in fruit 2-3.5 mm. long; margins whitish, or reddish white; plant 

 usually prostrate; leaves acute, 6-30 mm. long; achenes dull. 

 i LP. aviculare 



d. Calyx in fruit 3.5-5 mm. long; margins yellowish, or yellowish red; plant 

 erect; leaves 15-60 mm. long. 

 e. Leaves broadly elliptical, obtuse or subacute ; achenes dull. 



2. P. erectwm 

 e. Leaves narrowly elliptical or lanceolate ; achenes glossy. 



3. P. ramosissimum 

 c. Flowers in terminal spikes. 



d. Styles short, soft, barely exserted, withering in fruit. 

 e. Sheaths not ciliate, except rarely the uppermost. 

 /. Spikes several ; annual plants of damp rich soils. 



g. Peduncles obscurely glandular or smooth ; stamens 6. 



h. Achenes 1.5-1.8 mm. wide; spikes slender, drooping, pinkish or 

 purplish. 

 i. Leaves glabrous ; plant tall. 4. P. lapathi folium 



i. Leaves tomentose beneath ; plant low. 4a. P. lapathifolium, 



var. salicifolium 

 h. Achenes (1.8) 1.9-2.5 mm. wide; spikes thicker, erect, greenish. 



5. P. scabrum 



g. Peduncles strongly glandular-pubescent ; stamens 8 ; achenes 2.2-3.5 

 mm. wide; spikes "thick, erect, pink. 

 h. Leaves copiously strigose beneath and often above; uppermost 

 sheaths often ciliate; achenes 2.2-2.8 mm. wide. 



6. P. pennsylvanicum 

 h. Leaves glabrous or sparingly strigose on the midrib beneath ; 



sheaths usually not ciliate; achenes 2.5-3.5 mm. wide. 



6a. P. pennsylvanicum, 



var. laevigatum 



f. Spikes 1-2 (3) ; perennial aquatic or marsh plants, with long rootstocks 



rooting in the mud. 



g. Leaves elliptical or narrowly oblong-lanceolate, obtuse or subacute; 



spikes oval-oblong, 1.3-2.5 cm. long ; flowers bright pink. 



7. P. amphibium 



g. Leaves ovate-oblong or ovate-lanceolate, very acute or short-acumi- 

 nate; spikes oblong-linear, 3-9 cm. long; flowers deeper pink. 



8. P. coccinenm 

 e. Sheaths ciliate with a row of bristles. 



/. Sepals glandular-dotted. 



g. Achenes dull ; spikes strongly arched and nodding ; flowers greenish ; 

 stems often reddish ; internodes short, 2-A cm. long ; stamens 6. 



9. P. H yd ro piper _ 



g. Achenes glossy ; spikes erect or flexuous, not strongly nodding ; 

 flowers white, flesh color, or greenish white; stems green or green- 

 ish purple ; internodes longer, 3-8 cm. long. 

 h. Plant perennial; stems decumbent and submerged at base, rooting 

 at the nodes ; spikes erect, rather dense, peduncled ; flowers 

 whitish or pinkish ; stamens 8 ; achenes mostly 3-angled. 



10. P. robustius 



