This section is from the book "The Gardener V1", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
'American Cowslip ' - is a small group of pretty well known and much-admired hardy border plants. They are of simple accommodating nature, doing well in most soils and situations, but reach the greatest perfection in deep moist rich loam and in partial shade. Propagate by division in early spring, or by seeds, which they produce freely.
Dodecatheon Meaclia is the best-known species. The leaves are all radical, stalkless, oblong lanceolate, thin and soft in texture, and pale green, obscurely toothed, dying off shortly after flowering. The flower-stems are a foot or more high, bearing a considerable umbel of elegant drooping flowers of interesting shape. The flowers are rosy-purple, and divided into five broad much-reflexed segments. Flowers in April, May, and June, and in the north often blooming well through July. There are several varieties of this species of greater or less distinctness, which are often vended as species. The best of them are, Dodecatheon M. ele-gans, syn. giganteum, remarkable for greater luxuriance in all its parts, and rather more delicate colouring; Dodecatheon M. album, with white flowers suffused with rose; and Dodecatheon M. lilacinum, with rosy-lilac flowers.
Dodecatheon Integrifolium has oblong leaves destitute of teeth. The flower-stems are from 6 to 12 inches high. The inflorescence is the same as in Dodecatheon meadia, but the divisions of the corolla are more acute, and the colour is rosy-crimson. Flowers April, May, and June. W. S.