304 POLYGONACEeE. 



filiform. ACHENIA triangular or lenticular, usually covered 

 by the persistent calyx. — Eterbaa w • plants with jointed 

 stems, and small flowers in axillary and terminal fascicles and spikes, 

 or paniculate racemes. 



* Peksic.vrja, To urn. Fl owers in term inal or axillary 'piles, white or rose colored. 

 Mostly anni 



1. P. Pennsylvanicum, L. Pennsylvania, Knot- Grass. 



Stem smooth, tumid at the joints; leaves lanceolate, petiolate ; stipules smooth; 

 spikes oblong, crowded; stamens 8; styles 2 or 1. 



Margins of ponds and ditches. July — Oct. Slem 2 to 3 feet high, Le mm 3 to 5 

 inches long, % as wide, slightly scabrous. Spiket dense-flowered, largt and some- 

 what nodding. Flowers rose-colored, pedicellate. 



2. P. PebsiCARIA, L. L'idfs Thumb. Spotted Knot weed. 



Stem smooth; leaves lanceolate, pointed, roughish; sheaths fringed; tpUce* ovoid- 

 oblong or cylindrical, dense, ereet, on smooth peduncles; stamens mostly C; sty'es 

 2; united nearly half their length. 



Waste and damp place?, very common. July, Aug. Stem 12 to 18 inches high, 

 often colored. Leaves 2 to 4 inch a long, >4 as vide, usually marked with a dark 

 heart-shaped spot near the middle. Flowsrs greenish-purple, ia spikes about 1 

 inch long. 



3. P. LAPATniroLiUM, L. Pale Knotweed. 



Stem smooth, geniculate; terse* ovate-lanceolate or oblong-lanceolate, acuminata 

 smoothish, sometimes hairy beneath; upper sheaths somewhat fringed; spikes cy- 

 lindrical or oblong, erect or nodding; stamens mostly 6; styles 2, distinct and 

 at length divergent. 



Swamps and ditches, rare. An%. Stem 2 to 4 feet high. Leaves 3 to 5 inches- 

 long, }X to \% as wide, on petioles J-i to )< inch wide. Flowers small, white, or 

 tinged with red, in numerous panicled a 



4. P. Hydropiper. L. Water-pepper. Smart-weed. 



Smooth; leaves lanceolate, marked with pellucid dots, wavy -margined ; sheaths 

 inflated, fringed; spikes slender and interrupted, drooping- calyx dotted with 

 glands; stamens 6 to 8; styles 2 to 3, united at base; fruit lenticular or 3 sided. 

 (P. punctatum. Ell.) 



Low grounds, very common. Aug., Sept. A well known intensely acrid plant, 

 12 to 20 inches high, with the stem and leaves sprinkled with glandular dots. 

 Leaves 2 to 3 inches long, 1-5 as wide. Flow ,rs green, tinged with purple and 

 white. 



5. P. Hydropiperoides, Miehx. Mild Water-Pepper. 



Stem smooth, upright or ascending, of'en rooting at'thc joints along the base; 

 leaves lanceolate, roughish, slightly hairy or ciliate ; sheatJis fringed with long 

 bristles ; spikes slender, loosely flowered, weak ; stamens 7 to S ; styles 3, united bo- 

 low; fruit 3-sided, smooth and shining. 



Bwamps and along streams. July, Auar. Stem 12"to 15 inches high. Leavs 2 

 to 4 inches long, 1-5 as wide, sessile. Spikes several crowded near the summit of 

 the stem, composed of small fascicles of reddish flowers. (P. mite, Pers.) 



6. P. amphibium, L. Water Persicaria. 



Leaves elliptical-lanceolate or oblong, pointed or nearly obtuse, narrowed or 

 somewhat heart-shaped at the base ; spikes very dense, ovoid or cylindrical ; sta- 

 mens 5 ; styles 2;jruil flattened, smoothish. 



Marshes or ponds. July, Aug. A very variable species, embracing several d>»- 

 Unct varieties. Stem smooth, furrowed, short-jointed, often very long and creeping, 



