32. POLYGONACEAE 95 



4. Leaves oval to obovate, 1-2.5 cm wide; achenes brown, dull 

 or glossy; waste ground and disturbed soil. Aug.-Oct. 



[P. achonum Blake]. Erect Knolweed P. erccturn L. 



4. Leaves linear-oblanceolate to narrowly ellijitical, 2-5 mm 

 wide; achenes black, glossy; in sandy or alluvial soil. 



July-Oct. [P. exscrtum Small]. Bushy Knolweed 



P. ramosissinium Michx. 



2. Stem and branches erect, sharply 4-angled; inflorescence 

 slender; leaves plicate; sandy soil. July-Sept. Slender Knot- 

 weed P. tenue Michx. 



1. Flowers in terminal or axillary spikes or racemes. 

 5. Outer sepals not keeled or winged. 

 6. Style short; sepals usually 5. 



7. Stem glabrous or pubescent, not retrorsely bristly. 



8. Panicle terminal, usually solitary; perennial marsh or 

 aquatic or more or less amphibious herbs with long 

 rhizomes. 

 9. Panicle ovoid or ellipsoid, 1-3 cm long; leaves ellipti- 

 cal, glabrous, glossy above, obtuse or acute; shallow 

 water. June-Aug. [P. natans (Michx.) Eaton, non 

 Gueldenst.; P. amphibium of Am. auth., not L.]. 

 The terrestrial pubescent form with lanceolate, 

 acuminate leaves is f. hartwrightii (A.Gray) 

 G.N.Jones. Water Smartweed P. fluitans Eaton 



9. Panicle linear-cylindrical, 3-9 cm long, the peduncle 



glandular-hispidulous or strigose; leaves lanceolate, 

 acuminate; wet ground, common, except in the 

 southern counties. July-Oct. [P. emersum (Mich.x.) 



Britt.; P. muhlenbergii (Meisn.) Wats.] 



P. coccineum Muhl. 



8. Panicles usually several, axillary as well as terminal; 

 plants of moist rich soil. 



10. Stipular sheaths fringed with bristles. 

 11. Calyx glandular-punctate. 



12. Panicles erect; stamens 8; achenes glossy; wet 

 ground, common. July-Aug. Dotted Smart- 

 weed P. punctatum Ell. 



12. Panicles nodding in fruit; stamens 4 or 6; 



achenes dull; along ditches, common; nat. 



from Eur. Aug.-Oct. Water-pepper 



P. hydro pi per L. 



1 1. Caly.x not evidently punctate. 



13. Stems and peduncle glandular-hispidulous or 



pubescent; panicles nodding; flowers rose- 

 color; achenes lenticular; plants annual. 

 14. Leaves lanceolate; peduncles stijjitate- 

 glandular; achenes 1.8-2.5 mm long; 

 sandy soil, local; Kankakee Co. July- 

 Aug P. careyi Olney 



