This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
Slender herbs or more rarely shrubby, with simple leaves. Flowers axillary and solitary or geminate, or terminal and spicate or racemose. Calyx bilabiate, lips entire, ultimately closing over the fruit, and the upper one furnished with a helmet-shaped appendage which enlarges as the fruit is advancing towards maturity. Corolla-tube long, curved, dilated at the throat, naked within; upper lip entire or notched; lateral lobes of the lower lip usually connected with the upper, the central one spreading. Stamens 4; anthers cohering in pairs. A large genus, abundant in America, and scattered throughout the northern temperate regions. The genus is represented by two species in Britain, S. galericulata and S. minor; the former, common in England, has blue flowers; and the latter is a rather rare plant of very slender habit, with small pale pink flowers. They are known under the popular name Skull-cap. The generic name is from scutella, a dish, in reference to the form of the calycinal appendage.
1. S. macrantha. - A pretty perennial, usually less than a foot high. Leaves lanceolate, obtuse, eiliate. Flowers showy, violet-blue, in alternate axillary pairs, produced throughout the Summer. A native of Siberia.
2. S. alpina. - Of about the same stature as the last, with nearly sessile ovate-cordate toothed hairy leaves. Flowers in dense terminal spikes, wholly purple, or the lower lip of the corolla white or yellowish. A native of the mountainous parts of Europe and Asia, producing its flowers freely all the Summer.
3. S. Japonica. - A creeping species with obovate-spathulate leaves narrowed towards the base into a short petiole. Flowers in terminal spikes, bright blue or white. A profuse blooming plant from Japan.
S. villosa, from the Andes of Peru, has dense terminal spikes of showy scarlet flowers, and is rather tender. There are several other interesting hardy species, but the greenhouse species from Mexico greatly exceed them in the size and brilliancy of their flowers.