This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol2", 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 caulescent herbs, with descending or horizontal rootstocks. Stems sometimes woody at the base. Leaves alternate, with the stipules obsolete or appearing as narrow dilations at the base of the petiole, palmately 3-foliolate; leaflets broadly obcordate, usually inequilateral, nearly sessile or rarely stalked, sometimes sensitive. Flowers perfect, heterogonous or homogonous. Sepals 5, narrow, imbricated. Corolla yellow, sometimes with a darker eye. Petals 5, surpassing the sepals, rounded or notched at the apex. Stamens 10: filaments glabrous or the longer ciliate. Capsule more or less elongated, columnar or narrowed upward, angled, 5-celled. Seeds several in each cavity, transversely ridged or tuber-culate by broken ridges. [Greek, yellow-oxalis.]
About 50 species, of wide geographic distribution. Type species: Xanthoxylis corniculata (L.) Small.
Pedicels appressed-pubescent; cymes typically umbel-like.
Longer filaments glabrous.
Stem appressed-pubescent, not creeping; capsules pubescent.
Stem loosely pubescent; capsules glabrous except in No. 2, a plant with creeping stems.
Plants spreading and creeping; capsules pubescent.
Plants erect; capsules glabrous.
Cymes open at maturity; capsules gradually pointed.
Cymes cluster-like at maturity; capsules abruptly pointed.
Longer filaments pubescent.
Petals glabrous; pistil, or styles, short-hairy.
Stem and branches finely soft-pubescent or nearly glabrous; primary branches of the
cyme short or obsolete.
Leaves numerous; cymes mostly 1-flowered; capsules less than thrice as long as the
Leaves few; cymes mostly several-flowered; capsules over thrice as long as the calyx.
Stem and branches hirsute; primary branches of the cyme long; leaflets copiously
Petals pubescent; pistil, or styles, long-hairy.
Pedicels loosely pubescent.
Capsule-body several times longer than the sepals; leaflets uniformly green.
Capsule-body scarcely twice as long as the sepals; leaflets brown-margined.