POL YG ON A CEA E. 359 



Racemes erect. 



Style-branches scarcely or slightly exserted. 



Achene broadly oblong, biconvex. 5. P. Portoricense. 



Achene orbicular, flat. 8. P. Pennsylvanicum. 



Style-branches long-exserted ; achene ovoid, somewhat gibbous. 



9. P. iongistylum. 

 Ocreae fringed with bristles, their limbs not spreading. 



Racemes not interrupted, erect ; achene lenticular or 3-angIed. 

 Ocreae conspicuously fringed; achene broadly ovoid. 



10. P. Persicaria. 

 Ocreae inconspicuously fringed ; achene narrowly ovoid. 



11. P. persicarioides. 

 Racemes not interrupted, erect ; achene always 3-angled. 



Ocreolae conspicuously fringed. 14. P. Opelousanum. 



Ocreolae inconspicuously fringed. 



Leaves mostly glabrous above ; achene pointed at the top. 



15. P. Iiydropiperoides. 

 Leaves strigose above ; achene pointed at both ends. 



13. P. setaceum. 



Racemes not interrupted, drooping. 12. P. Careyi. 



Racemes interrupted, erect or drooping. 



Achene granular and dull ; racemes drooping. 16. P. Hydropiper. 

 Achene smooth, shining ; racemes erect. 17. P. punctatum. 



Ocreae fringed with bristles, their limbs normally spreading. 



18. P. orientale. 



2. Flowers in long naked much interrupted spike-like racemes; calyx 4- parted. 



19. P. Virginianum. 

 3. Flowers in axillary clusters; stems more or less wiry, not twining. 



Plants prostrate ; achene invested by the calyx. 



Achene pointed at the apex, rounded at the base. 



Leaves mostly acute ; style 3-parted to below the middle. 



20. P, aviculare. 

 Leaves mostly obtuse; style 3-parted to the base. 21. P. Httorale. 



Achene pointed at both ends. 22. P. Bellardi. 



Plants prostrate ; achene protruding beyond the calyx. 



Leaves mostly longer than the internodes ; sea beach species. 



23. P. maritimum. 



Leaves shorter than the internodes ; plant of waste places. 24. P. Rayi. 

 Plants erect or ascending, rather stout. 

 Achene invested by the calyx. 



Leaves oval, oblong or obovate, persistent. 25. P. erectum. 



Leaves narrowly lanceolate or linear-oblong, persistent. 27. P. ramosissimum. 

 Leaves oblong-lanceolate or narrowly oblong, fugacious. 



28. P. camporum. 



Achene much exserted beyond the calyx. 26. P. exsertum. 



Plants strictly erect and very slender. 



Leaves with a lateral impression on either side of the midvein ; fruiting pedicels 



stout, erect. 29. P. tenue. 



Leaves without lateral impressions ; fruiting pedicels slender, deflexed. 



30. P. Douglasii. 



4. Flowers in axillary and terminal clusters, racemes or panicled racemes; stems 



mostly twining. 



Stems twining ; herbaceous vines. 



Outer segments of the calyx unchanged, or keeled in fruit. 



Achene granular and dull ; ocreae not bristly. 31. P. Convolvulus. 



Achene smooth and shining ; ocreae bristly. 32. P. cilinode. 



Outer segments of the calyx conspicuously winged in fruit. 

 Calyx-wings not incised. 



Fruiting calyx 10-12 mm. long, the wings crisped. 33. P. scandens. 

 Fruiting calyx 6-8 mm. long, the wings rather flat. 34. P. dtemeforum. 

 Calyx-wings incised. 35. P. cnstatum. 



Stems stout, erect, tall ; outer calyx-segments winged in fruit. 36. P. Zuccarinii. 



5. Flowers in capitate clusters or racemes; stem climbing by recurved prickles. 

 Leaves sagittate: achene 3-angled. 37. P. sagittatum. 



Leaves halberd-shaped; achene lenticular. 38. P. ari folium . 



I. Pclyeronum viviparum L. ALPINE BISTORT. (I. F. f. 1318.) Perennial 

 by a corm-like rootstock, mostly glabrous and somewhat glaucous ; stems solitary 



