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 acaulescent or leafy-stemmed herbs, some species very woody at the base, with simple or branched, often tufted stems, and entire alternate opposite or whorled leaves. Flowers small, fascicled, cymose, umbellate or capitate, subtended by 5-8-toothed or cleft campanulate top-shaped or almost cylindric involucres. Calyx 6-cleft or 6-parted, usually colored, the segments equal or the outer ones larger. Stamens 9, included or exserted; filaments filiform, often villous. Style 3-parted; stigmas capitate. Achene pyramidal, 3-angled, more or less swollen near the base, invested by the calyx-segments, or winged. Embryo axial or somewhat eccentric. [Greek, referring to the woolly and jointed stems.]
Over 200 species, natives of America, mostly of the western United States. Type species:
Eriogonum tomentosum Michx.
Achenes merely angled, never winged.
Calyx contracted into a stipe-like base.
Caulescent; stems topped by compound cymes.
Stem leaves alternate.
Stem leaves opposite or whorled.
Calyx yellow; basal leaves rounded at the base; Alleghanian.
Calyx white or pink; basal leaves narrowed at the base; campestrian
Scapose; stems topped by simple umbels.
Calyx jointed to the pedicel without a sripe-like base.
Scapes or peduncles topped by capitate clusters.
Calyx glabrous; achenes over 2 mm. long.
Calyx villous; achenes less than 2 mm. long.
Scapes or peduncles topped by more or less compound cymes.
Ovaries and achenes completely clothed with wool; leaf-blades silky above with silvery
Ovaries and achenes glabrous or villous at the top; leaf-blades more or less floccose.
Annual; herbaceous throughout and usually simple at the base.
Perennial; shrubby and much branched at the base.
Calyx white, pink or reddish.
Leaf-blades copiously pubescent on both sides.
Leaf-blades densely pubescent beneath, inconspicuously so above."
Inflorescence 2-3 times compound; branches spreading.
Inflorescence 5-7 times compound; branches erect or nearly so.
Involucres on drooping or deflexed peduncles.