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.
Erect herbaceous perennials; roots often fleshy. Leaves usually with conspicuous transverse veins. Flowers in simple terminal or extra-axillary umbels. Lobes of the corolla long and narrow, reflexed. Within the petals there is a coronet seated upon the combined filaments, composed of 5 boat-shaped processes having 5 projecting horns. Stamens 5, inserted upon the base of the corolla. Pollen-masses 10, waxy, fixed to the stigmas in pairs. Follicles normally 2, not coriaceous. Seeds bearing a tuft of silky hairs at one end. There are upwards of twenty-five species, mostly from America, many of which occur in the temperate regions of the North. The name is the Greek form of AEsculapius, to whom the genus is dedicated.
1. A. tuberosa. Butterfly-weed or Pleurisy-root. - An erect hairy plant about 18 inches high. Leaves linear to oblong-lanceolate, nearly sessile. Flowers small, numerous, terminal, or towards the summit borne in corymbose umbels. Petals green tinged with orange. Hoods of the coronet oblong, bright orange-red, and more conspicuous than the petals. Seed-vessel hoary, not prickly. A native of dry localities in North America, producing its brilliant flowers nearly all the Summer.
2. A. Cornuti, syn. A, Syriaca. Milkweed or Silkweed.-A robust-growing leafy species from 3 to 4 feet high. Leaves large, ovate or oblong, downy beneath, and distinctly petiolate. Flowers fragrant, larger than in the preceding, dull purple; hoods of the crown ovate, with 2 lateral teeth. Seed-vessel covered with soft prickles. A native of North America only, the second name having been misapplied.
The foregoing species are the only ones at all common in gardens, but there are several others equally handsome and effective where there is ample space for large subjects. A, Dougldsii has purplish-lilac sweet-scented flowers; A. incar-ndta purple and flesh-coloured; A. variegata purple and white.