BUCKWHEAT FAMILY 71 



Calyx mostly 5-parted, the divisions petal-like, erect and per- 

 sistent. Stamens 3-9 ; styles 2-3-parted. Fruit lens-sliaped 

 or 3-angled.* 



1. P. aviculare L. Knotgrass. Annual or perennial. Stem pros- 

 trate or ascending, diffuse, smooth, 6-24 La. long. Leaves small, 

 lanceolate or linear-oblong, obtuse, nearly or quite sessile. Sheaths 

 thin and dry, 2-3-cleft or cut. Flower clusters axillary, 1-5-flowered ; 

 flowers inconspicuous, nearly sessile. Calyx greenish-white, 5-parted, 

 the lobes with white or colored borders. Stamens 5-8 ; style 3-parted. 

 Akene 3-angled, not shining. A common weed in dooryards and where 

 the gromid is trampled.* 



2. P. lapathifolium L. Annual. Stem branching, 1-4 ft. high. 

 Leaves lanceolate or broader, wedge-shaped at the base and taper- 

 ing from near the base to an extremely slender point, ciliate, vary- 

 ing greatly in length. Sheaths not ciliate or fringed. Spikes oblong 

 to linear, closely flowered, erect or nearly so, ^-2 in. long. Calyx 

 white or pink. Stamens 6 ; style 2-cleft. Akene ovate, lens-shaped, 

 ■5J5 in. wide or less. In wet soil. 



3. P. acre HBK. Water Smartweed. Perennial. Smooth or 

 nearly so ; stems erect or ascending, rooting below, 2-5 ft. high. 

 Leaves lanceolate or broader, tapering at both ends, petioled, ciliate, 

 translucent-dotted, acrid, 1^8 in. long. Sheaths cylindrical, falling 

 early, bristly-fringed. Spikes erect or nearly so, loosely flowered, |-3 

 in. long. Calyx whitish-greenish or flesh color. Stamens 8 ; style 

 usually 3-parted. Akene oblong, lens-shaped, smooth and shining. 

 Swamps and wet soil, especially S. 



4. P. Persicaria L. Lady's Thumb. Annual. Smooth or nearly so. 

 Stem erect or ascending, 6-24 in. high. Leaves lanceolate or nar- 

 rower, tapering at both ends, usually with a dark triangular or cres- 

 cent-shaped spot near the center, very variable in length. Sheaths 

 more or less bristle-fringed. Spikes ovoid or oblong, dense, erect, 

 peduncled, |-2 in. long. Calyx pink or purple. Stamens usually 6 ; 

 Styles 2-3-cleft more than half their length. Akene broadly ovate 

 and lens-shaped, often somewhat triangular, smooth and shining. In 

 waste ground, often a troublesome weed. Naturalized from Europe. 



5. P. hydropiperoides Michx. Mild Water Pepper. Perennial. 

 Stem smooth, slender, erect, decumbent, or prostrate, 1-3 ft. long. 

 Leaves usually narrowly lanceolate, but variable, acute, ciliate, 2-6 

 in. long. Sheaths wrinkled, bristle-fringed. Spikes erect, slender, 

 often with the flowers scattered, ^-2} in. long. Calyx pale pink, 

 greenish or nearly white. Stamens 8 ; style 3-parted more than half 

 its length. Akene 3-angled, smooth and shining. In swamps and 

 wet places, especially S. 



