(Some plants in the Asteraceae contain hepatotoxic pyrrolizidine alkaloids. Coltsfoot is among them. More info here: Livertoxic PAs --Henriette.)
Coltsfoot. N. F. IV. Farfara. Coltsfoot Leaves. Tussilago Leaves. Folio, Farfarae, P. G. Tussilage, Pas d'ane, Fr. Huflattig, Rosshuf, G.—"The dried leaves of Tussilago Farfara, Linne (Fam. Compositae), without the presence of more than 5 per cent. of other parts of the plant or other foreign matter." N. F. Coltsfoot is a low perennial herb, indigenous to Europe and growing in wet places from Quebec to Pennsylvania and westward to Minnesota. It possesses a horizontal rhizome from which, early in the spring, arise several leafless, erect, simple, unifloral scapes or flower-stems and bearing appressed scale-like bracts of a brownish-pink color. The flower, which stands singly at the end of the scape, is large, yellow, compound. The leaves do not make their appearance until after the flowers. The flowers have an agreeable odor, which they retain after desiccation. The dried root and leaves are inodorous, but have a rough, bitterish, mucilaginous taste.
The leaves are described as "petioles long, pubescent; blades very brittle, nearly orbicular or broadly ovate-reniform, from 8 to 15 cm. in length and nearly as broad, deeply cordate at the base, angulately lobed and dentate with red-brown teeth, palmately five- to nine-veined; young leaves white floccose all over, the older leaves with upper surfaces dark green and nearly smooth, the younger densely white floccose. Odor indistinct; taste mucilaginous, faintly herbaceous, bitter. The powder, when examined under the microscope, exhibits numerous multicellular, non-branching hairs, usually curved and twisted together, We lower cells about 0.035 mm. in width, the terminal cells much elongated, about 0.012 mm. in width and at times with spiral bands; broadly elliptical stomata about 0.05 mm. in length and associated with finely striated epidermal cells, the latter having wavy vertical walls; non-porous sclerenchymatous fibers few with walls from 0.006 to 0.01 mm. in thickness; parenchyma cells containing chloroplastids; tracheae few, spiral, annular or with simple pores. Coltsfoot yields not more than 20 per cent. of ash." N. F. Boiling water extracts their virtues. C. S. Bondurant (A. J. P., 1887, 340) examined coltsfoot chemically. He found evidences of a bitter glucoside. Klobb isolated two phytosterols from coltsfoot flowers. (P. J, 1909, 999.) Coltsfoot exercises little sensible influence upon the human system. It is, however, demulcent, and is sometimes used in chronic coughs, consumption and other affections of the lungs. The expectorant properties which it was formerly thought to possess are not obvious. The leaves were smoked by the ancients in pulmonary complaints, and in Germany they are said to be substituted for tobacco. In the N. F. they are used in a pectoral tea. Cullen used the fresh juice in scrofula,, several ounces daily. Dose, of the dried leaves, one to two drachms (3.9-7.5 Gm.), which may be conveniently given in decoction.
The Dispensatory of the United States of America, 1918, was edited by Joseph P. Remington, Horatio C. Wood and others.