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.
Succulent usually prostrate herbs with alternate opposite or whorled leaves, seldom in rosettes. Parts of the flower in fives or fours; stamens twice as many as petals. 120 species, chiefly from the temperate and frigid zones of the north. Name from sedeo, to sit, referring to the prostrate habit of most species on rocks and stones.
1. S. acre. Biting Stonecrop, Wall Pepper, or Poor Man's Pepper. - This indigenous trailing yellow-flowered species is perhaps the commonest in cultivation. It spreads so rapidly that it is well suited to cover rock-work, etc. It is quite glabrous, with small scale-like imbricate leaves and numerous flowers rising only a few inches from the ground.
2. S. reflexum. - Another yellow-flowering species, growing from 6 inches to a foot high. Leaves crowded, cylindric, re-flexed, about an incli long. Flowers in terminal flat cymes. This species spreads very fast, and has become naturalised in several parts of Britain.
3. S. album.- Flowering-stems erect. Leaves glabrous, cylindric, oblong, about 6 lines long. Flowers white. A native of North Britain.
4. S. Telephium, syn. S. purpureum. Orpine. - Stems about a foot high. Leaves broad, 1 to 3 inches long, ovate or oblong, flat or concave, obtusely serrate. Flowers rose, purple, white, or speckled, in dense corymbose cymes. An indigenous plant.
5. S. Rhodiola. Rose-root. - This species has dioecious flowers. It grows about a foot high, with obovate or lanceolate acute glaucous leaves toothed towards the tip, the upper ones largest. Flowers purplish or yellow, in compact cymes. A native species, frequently seen in old gardens.
6. S. Sieboldii. - A distinct species with erect or ascending-slender stems. Leaves opposite or in threes, flat, orbicular, and glaucous. . Flowers in dense corymbs, very showy, pink or red. A native of Japan, and an old inhabitant of our gardens. There is a variegated form.
7. S. Fabaria. - Near the foregoing, but taller and handsomer, and also a native of Japan. Leaves broadly oval, crenate. Flowers rosy purple. Both this and the last bloom towards the end of Summer.
8. S. Ewersii. - A dwarf species with glaucous oblong-orbicular crenate flat glabrous leaves and rosy purple flowers in large corymbs. One of the best. A native of Siberia, flowering in Summer.