An Illustrated Flora of the Northern United States, Canada and the British Possessions/Polygonaceae

Flowers or flower-clusters subtended by involucres. Ocreae present; calyx 2-4-parted; stamens 3 or fewer. Ocreae none; calyx 6-cleft or 6-parted; stamens 9; achene 3-angled. Flowers or flower-clusters not involucrate; stamens 4-8. Stigmas tufted; sepals of the inner row usually accrescent. Calyx 6-parted; style 3-parted; achene 3-angled. Calyx 4-parted; style 2-parted; achene lenticular. Stigmas capitate, 2-cleft or toothed; sepals of the outer row often accrescent or reflexed. Floral tube obscurely or only slightly developed; stigmas not 2-cleft; ovule erect. Internodes of the stem and branches not adnate; plants not heath-like; sepals of the outer row often winged. Leaf-blades jointed at the base; ocreae 2-lobed, becoming lacerate; filaments, at least the inner, dilated. Leaf-blades not jointed at the base; ocreae various, not 2-lobed; filaments slender. Ocreae cylindric, truncate. Sepals 4; calyx curved; stamens 4. Sepals 5, if fewer, the stamens more than 5; calyx not curved. Ocreae oblique, more or less open on the side facing the leaf. Plants with fleshy rootstocks, scaly caudices and simple flower-stems; leaves mostly basal; inflorescence simple; styles elongated. Plants with fibrous roots or slender rootstocks, without scaly caudices, with branching stems; leaves not basal; inflorescence branched. Sepals neither keeled nor winged. Racemes collected into terminal corymbs; embryo dividing the endosperm by an S-shaped curve; plants smooth. Racemes not in terminal corymbs; embryo slender, at one side of the endosperm; plants prickle-armed. Sepals, at least the outer ones, keeled or winged. Stigmas rounded capitate; styles short, erect, or none. Stigmas dilated, toothed; styles divaricate. Internodes of the stem and branches partially adnate; plants heath-like; sepals of the inner row often winged. Floral tube well developed, enclosing the achene, winged; stigmas 2-cleft; ovule pendulous.