This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol1", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Annual or perennial, often pubescent or glandular caulescent herbs, various in habit, never twining nor climbing. Leaves alternate, entire, continuous with the ocreae, often glandular-punctate. Ocreae cylindric, mostly membranous, truncate, naked, ciliate or fringed with bristles. Racemes spike-like, varying from linear to ovoid, dense and erect, or few-flowered, lax and drooping. Ocreolae funnelform, naked, ciliate or fringed. Pedicels rather stout, articulated at the base of the calyx. Calyx more or less colored, varying from white and green to red, often glandular-punctate, investing the achene. Sepals mostly 5, 2 wholly exterior, 2 wholly interior and 1 with one margin interior and the other exterior, none of them winged or keeled. Stamens varying from 4 to 8, included or exserted; filaments not dilated, erect or nearly so. Styles mostly 2, sometimes 3, usually partially united, included or exserted; stigmas capitate. Achene mostly lenticular, sometimes 3-angled and lenticular on the same plant, usually black, smooth or granular. Endosperm horny. Cotyledons accumbent. [From Pcrsica, from the resemblance of the leaves to those of the peach.]
About 125 species, widely distributed. Type species: Polygonum Persicaria L.
Racemes solitary or paired.
Raceme short and stout; leaves obtuse or merely acute.
Raceme long and slender; leaves acuminate.
Racemes several or numerous.
Ocreae not fringed with bristles.
Style and stamens included or slightly exserted; achene-faces concave.
Achene biconvex, broadly oblong; plants perennial.
Achene concave, orbicular; plants annual.
Style or stamens conspicuously exserted; achene-faces swollen.
Ocreae without spreading borders; leaves relatively narrow, short-petioled or sessile; stigmas minute.
Stem, branches and peduncles rough-glandular.
Stem, branches and peduncles not rough-glandular.
Sepals not glandular-punctate.
Racemes short, stout and compact.
Ocreae inconspicuously fringed; achene narrowly ovoid. 8.
Ocreae conspicuously fringed; achene broadly ovoid.
Racemes slender, elongated and lax or interrupted.
Ocreae strigose, fine-bristly; leaves glabrous or somewhat strigose.
Calyx greenish-white; ocreolae copiously long-bristly.
Calyx white, pink or purplish-pink; ocreolae sparingly fine-bristly.
Ocreae hirsute or appressed-hirsute, coarse-bristly; leaves conspicuously ap-
Achene granular and dull; racemes drooping.
Achene smooth and shining; racemes erect.
Ocreae with spreading border; leaves broad, long-petioled; stigmas large.