Alkanna root is obtained from Alkanna tinctoria, Tausch. (N.O. Boragineae), a herbaceous plant, growing in Hungary, the Grecian Archipelago, and Asiatic Turkey. The simple tapering roots are of a deep reddish-purple colour, and crowned by the remains of leaves, which bear whitish, bristly hairs. The roots have little odour or taste, and readily colour the fingers when handled. They vary commonly from 10 to 15 centimetres in length and 1 to 2 centimetres in thickness. The external surface is deeply furrowed and the outer layers readily exfoliate in papery strips. The furrows are often so deep as to separate the whitish wood into isolated strands, these changes being due to the destruction of the parenchymatous tissue by conversion into colouring matter.
Constituents.—The root contains two red substances of an acid nature, namely anchusic and alkannic acids; alkalies change the colour of the former to green and of the latter to blue. The root yields from 5 to 6 per cent. of a red, amorphous, oleoresinous substance, to which the name of alkannin has been given. This colouring matter is readily soluble in oils, and is employed as a reagent for the detection of oil in vegetable microscopical research, the solution being prepared by dissolving the alkannin in absolute alcohol, adding an equal volume of water, and filtering. The roots of Onosma echioides, Linn., and of Macrotamia cephalotes, DC., contain a colouring matter similar to that found in alkanna root.
Uses.—Alkanna root is used for colouring lip salves and similar toilet preparations of an oily or spirituous nature. The fine red colouring matter is incompatible with alkalies.