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..
Buckwheat Family. Herbs, vines, shrubs or trees, with alternate or sometimes opposite or whorled simple mostly entire leaves, jointed stems, and usually sheathing united stipules (ocreae). Flowers small, perfect, dioecious, monoecious or polygamous, spicate, racemose, corymbose, umbellate or panicled. Petals none. Calyx inferior, free from the ovary, 2-6-cleft or 2-6-parted, the segments or sepals more or less imbricated, sometimes petaloid, sometimes developing wings in fruit. Stamens 2-9, inserted near the base of the calyx, or in staminate flowers crowded toward the centre; filaments filiform or subulate, or often dilated at the base, distinct or united into a ring; anthers 2-celled, the sacs longitudinally dehiscent. Pistil solitary; ovary superior, 1-celled; ovule solitary, orthotropous, erect or pendulous; style 2- or 3-cleft or 2- or 3-parted (rarely 4-parted), sometimes very short; stigmas capitate or tufted, rarely 2-cleft or toothed; fruit a lenticular, 3-angled or rarely 4-angled achene, usually invested by the persistent calyx; endosperm mealy or horny; cotyledons accumbent or incumbent, flat; embryo straight or curved.
About 40 genera and 800 species, of wide geographic distribution.
* Text contributed by Dr. John Kunkel Small.
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.