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.
Herbs or underslimbs with viscid or hairy rarely glabrous foliage and terminal panicles or cymes of white, yellow, orange, purple, brown, violet or spotted showy flowers. The corolla affords the most striking character of this genus. It is 2-lipped, the upper one being small, and the lower large and inflated, bearing some resemblance to a slipper in some species, hence the generic name from the Latin calceolus, a shoe. In C. jovellana, however, the lips are nearly equal. Stamens 2. Capsule 2-celled, subtended by the somewhat enlarged calyx. The species are mostly natives of South America, two extending to New Zealand. All those mentioned below are from South America.
1. C. integrifolia. - An erect shrubby species, glabrous, pubescent, or viscid. Leaves varying from linear-lanceolate to ovate, crenate, rugose, narrowed into a short petiole. Flowers numerous, corymbose, yellow.
2. C. amplexicailis. - This species has ovate-lanceolate sessile stem-clasping crenate very hairy leaves and corymbose panicles of yellow flowers. C. crenata is a closely allied species with sessile leaves and very numerous though rather smaller flowers.
In addition to the foregoing there are several nearly or quite hardy species, which will nourish in the warm humid climate of the South-west of England and Ireland; but they appear to be very rare, and probably some of the best are no longer to be found in cultivation. C. Fothergillii is one of the hardiest herbaceous kinds, being found as far south as the Falkland Islands. It is a dwarf glandular pubescent herb with villous petiolate spathulate leaves and long narrow yellow and purplish brown flowers. C. plantaginea is an herbaceous scapose Chilian species with broad radical leaves and few yellow flowers spotted with red, on naked scapes about 9 inches high. C. Kellyana is a hybrid form, said to be quite hardy, and probably the issue of a cross between the last-named and another species. C. corymbosa has numerous yellow flowers. C. arachnoidea is an erect branching species about 2 feet high, having the spathulate leaves clothed with a dense whitish cobweb-like down and terminal clustered purplish red flowers. C. alba is a shrubby species with linear remotely toothed leaves and showy white flowers. C. violacea, syn. C. jovellana, has small ovate coarsely-toothed leaves and violet-purple flowers.
Very few of the pure species are cultivated, but the hybrid forms are numerous. They have been raised from C. amplexicaulis, C. integrifolia, syn. C. rugdsa, C. corymbosa, G. pmypurea, C. arach-noldea, C. thyrsifiord, etc.