Order 103.— KNOT WEEDS. 291 



a Calyx unequally 4-cleft. Styles 2, long, deflexed. . . .16 

 a Calyx equally 5-parted. Styles erect. .. .b 

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



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



c Flovv'^.rs in leafless, terminal, spike-like racemes.... d 

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



d Raceme one, dense. Stems decumbent at base 13, H 



d Eacemes several. Sheaths naked, not fringed 11 'l2 



d Eacemes several. Sheaths bristly friuge-ciliate e 



e Style 2 (or 3)-cleft. Achenia flat or lens-shaped .... 8-1 



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, 3-anu-led 1 2 

 1 P. avicula're. Bird K. Prostrate or erect. Leaves emptic-lanc'eolate, acutish at 



each end. Achenia striate, dull. Very common 

 2P.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. LaTce K. Erect, much brandied,' 2-3f. hi-h. Leaves 



lauce-oblong or linear. Achenia smooth, dull W 

 oP.hirsu'tum. //ai.j, ^ Hairy-tawny. Leaves lanceolate* from a blunt base. S. 



6 P. hydropiperox des. Mxld Water-pepper. Stem smooth. Leaves linear-lanceolate 



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



7 P. acre 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, noddmg. Calyx dotted. Achenia roughened 

 9P.Car^eyi Carei/s K. Plant hairy. Spikes nodding, on very Ion. stalks 

 10 P.PersicaMa. Ladrfs-thumh. Leaves marked witli a brown spot Si-ikea 



short, dense, erect. Achenia shining, flattened 



11 P. Pennsylvan'icum. PenmyUania K. Spikes oblong, dense, with ^dandular- 



hispul stalks and pedicels. Achenia with flat sides c 



12 P.incarnaW Flesh-red K. Spikes linear, nodding, the stalks and branches 



glandular-dotted. W. S. "'u.ns 



18 P amphibW. Water K. Stem ascending from a prostrate, rootin. base 

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



UP.viviparum^/^/^,^,-,^,,^. Creeping at base. Lvs. lance-hnean Mts N 

 ;rP V ..f '^^'-^'l^^f -• Stem stout, tall, with large, drooping spikes". \ 

 16P.V.rg.xuaW Up-Ji. K. Leaves large. Eacemes slender, flou;,-8 ren.ote 

 7P.convorvulus. Kuot-BMu^eed. Roughish. E.cemes axillary'. Fruit dull 

 P.c..no'de. Bearded B Sheaths with a hairy ring. Panicles axil, and erminal 



20 P. sagma turn. Scratch-gra.s. Lvs. lance-sagittate. Stamens 8. Styles 3 



21 P. arxfo hum. Aram-lv. S. Lvs. j.olnted, with pointed lobes. Stain. 6." Stv. 2. 



