This section is from the book "Commercial Gardening Vol2", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
Out of some 300 species only a few are grown largely. The most popular is the variegated form of M. cordifolium, which has small heart-shaped leaves bordered with creamy white, and bears masses of bright rose-purple blossoms. It is largely grown for carpet bedding, and is sold in shallow boxes. Propagation is effected by cuttings from stock plants inserted in a gritty compost under glass from February to April.
Other species are M. crystallinum (the Ice Plant), M. tricolor, and M. pomeridianum, all annuals easily raised from seeds sown in heat in spring. The Ice Plant is so called owing to the large glittering crystallike granules which give the ovate wavy leaves a frosted appearance. M. pomcridianum has yellow flowers like those of Sweet Sultan, but they only open in the evening. M. tricolor has pink-, crimson-, and white-flowered varieties.