POLYGONACEAE 115 



Ocreae cylindric, truncate or with a spreading limb. 

 Sepals 4 : calyx curved : stamens 4. 6. P. Virginianum. 



Sepals 5, if fewer the stamens more than 5 : calyx not curved. 

 Racemes solitary or 2 : plants mainly aquatic. 

 Ocreae without spreading borders. 

 Leaf-blades with more or less acuminate tips. 



7. P. emersum. 

 I,eaf-blades blunt or merely acute at the apex. 



8. P. amphibium. 

 Ocreae with spreading borders. 9. P. Hartwrightii. 



Racemes several or numerous : plants mainly terrestrial. 

 Ocreae without spreading limbs. 

 Ocreae naked or merely ciliolate. 

 Racemes more or less drooping. 

 Styles united only at the base. 10. P. incarnalum. 



Styles united to beyond the middle. 11. P. lapathifoHum. 

 Racemes erect. 12. P. Pennsylvanicum. 



Ocreae fringed with bristles. 

 Racemes erect. 

 Flower-clusters contiguous or mainly so. 

 Achenes lenticular. 13. P. Persicaria. 



Achenes 3-angled. 

 Racemes oblong-cylindric. 13. P. Persicaria. 



Racemes linear. 14. P. hydropiperoides. 



Flower-clusters mostly separated. 15. P. punctatum. 



Racemes drooping. 

 Flower-clusters contiguous : foliage strigose. 



16. P, Careyi. 

 Flower-clusters mostly separated : foliage glabrous or nearly so. 



17. P. Hydropiper. 

 Ocreae with spreading limbs. 18. P. orientate. 



Ocreae oblique, more or less open on the side facing the leaf. 

 Sepals neither keeled nor winged. 

 I,eaf-blades sagittate : achenes 3-angled. 19. P. sagittaium. 



Leaf-blades hastate : achenes lenticular. 20. P. arifotium. 



Sepals keeled or winged, conspicuously so at maturity. 

 Stems stout, erect, not twining. 21. P. Zuccarinii. 



Stems relatively slender, twining. 

 Outer sepals keeled at maturity. 

 Inflorescence consisting mostly of axillary and terminal clusters and 



simple racemes : achene granular. 22. P. Convotvulus. 



Inflorescence consisting mostly of axillary and terminal panicled 

 racemes : achene smooth. 23. P. cilinode. 



Outer sepals developing conspicuous wings. 

 Sepal-wings not incised. 24. P. scandens. 



Sepal-wings incised. 25. P. cristatum. 



1. Polygonum aviculare L. Knotweed. Door-weed. (Man. p. 

 363 ; I. F._/. 1337.) In cultivated and waste grounds, almost through- 

 out N. Am. Asia and Eu. — Pennsylvania : Northampton ; Chester ; 

 Bucks ; Erie ; Lancaster ; Monroe ; Franklin ; Delaware ; Ai<- 

 legheny. 



