OUDEU 102. KNOTWEEDS. 291 



a Calyx unequally 4-cleft. Styles 2, long, deflexed....!6 



a Calyx equally 5-parted. Styles erect b 



b Sheaths with a spreading border. Stamens 7. Plant tall 15 



Sheaths not bordered. Stamens 5, 6, or 8 c 



6 Flowjrs in leafless, terminal, spike-like racemes d 



c Flowers axillary, or rarely forming a leafy raceme. . . .f 



d Kaceme one, dense. Stems decumbent at base. . . .13, 14 

 d Kacemes several. Sheaths naked, not fringed.... 11, 12 

 d Kacemes several. Sheaths bristly fringe-ciliate. . . .e 



e Style 2 (or 3)-cleft. Achenia flat or lens-shaped.... 8-10 

 e Style 3-cleft. Achenia sharply 3-cornered. Wet.... 5-7 



f Achenium protruding beyond the calyx, 3-angled 3, 4 



f Achenium included in the calyx, 8-angled 1, 2 



1 r. avicula're. Bird K. Prostrate or erect. Leaves elliptic-lanceolate, acutifrh at 



each end. Achenia striate, dull. Very common. 



2 P. ten'ue. Slender K. Slender, rigidly erect. Leaves lance-linear, erect, acute. 



3 P. marit'imum. Sea K. Prostrate, diffuse, glaucous, close-jointed. Leaves 



linear-oblong, fleshy. Achenia smooth, shining. E. 



4 P. ramosis'simum. Lake K. Erect, much branched, 2-3f. high. Leaves 



lance-oblong or linear. Achenia smooth, dull. W. 



5 P. hirsu'tum. Hairy K. Hairy-tawny. Leaves lanceolate from a blunt base. S. 

 G P. hydropiperoi'des. Mild Water pepper. Stem smooth. Leaves linear-lanceolate, 



not acrid, tapering at both ends. Spikes slender. Calyx dotless. 

 7 P. aere. Sharp W. Stem smooth. Leaves biting, dotted as well as the calyx, 



lanceolate, pointed. Spikes very slender, thread-form. 



8 P. hydropi'per. Water-pepper. Smooth. Leaves very biting, dotted. Spikes 



short, nodding. Calyx dotted. Achenia roughened. 



9 P. Car'eyi. Carey's K. Plant hairy. Spikes nodding, on very long stalks. 

 10 P. Fersica'ria, Ladi/ s-thumb. Leaves marked with a brown spot. Spikes 



short, dense, erect. Achenia shining, flattened. 



11 P. Pennsylvan'icum. Pennsylvania K. Spikes oblong, dense, with glandular- 



hispid stalks and pedicels. Achenia witli flat sides, c. 



12 P. incarna'tum. Flesh-red K. Spikes linear, nodding, the stalks and branches 



glandular-dotted. W. S. 



18 P. amphib'ium. lVa(er K. Stem ascending from a prostrate, rooting base. 

 Leaves lance-oblong. Stamens 5. Spikes large, dense, rose-red. 



1 4 P. vivip'arura. Alpine Bistort. Creeping at base. Lvs. lance-linear. Mts. N. 

 !5 P. orienta'le. Princes Feather. Stem stout, tall, with large, drooping spikes, f 



16 P. Virginia 'num. Lip-ft. K. Leaves large. Kacemes slender, flowers remote. 

 17 P. convolvulus. Knot- Bindweed. Roughish. Racemes axillary. Fruit dull. 

 ISP. cilino'de. Bearded B. Sheaths with a hairy ring. Panicles axil, and termira?. 

 10 P. dnmito'rum. Hedge B. Calyx with the 3 outer sepals acutely wing-keeled. 



20 P. sagitta'ttun. Scratch-grass. Lvs. lance-sagittate. Stamens 8. Styles S. 



81 P. arifo'Uum. Arui*-lo. S. LVB. pointed, with poiuted lobes. Stain. 6. Sty. 2. 



