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 erect or prostrate shrubs with usually opposite simple fleshy leaves very variable in form, and conspicuous white, yellow or red flowers resembling some of the Compositeae in appearance, though widely different in structure. Calyx-tube adnate to the ovary, limb 5- to 8-lobed. Petals linear, numerous, in one or more series. Stamens numerous. Capsule contained in the fleshy calyx-tube, usually 5-celled, opening through the top of the cells, many-seeded. The species are estimated at about 300, the majority inhabiting South Africa. The name is a compound of mid-day, and a flower; the flowers of many species do not expand except when the sun shines upon them.
1. M. crystallinum. Ice Plant. - This very remarkable plant is a native of the South of Europe. It is a dwarf branching annual with alternate or opposite oblong-undulate sessile leaves which as well as the stem are covered with crystalline granules. The flowers are solitary and axillary, either pink or white, with a yellow centre.
2. M. cordifolium. - This is a perennial species, and better known by the variegated form, which is in great request for bedding in Summer. The habit is dwarf and dense, with small cordate leaves and sessile purple flowers. South Africa.
3. M. tricolor. - A pretty tender annual species, growing in dense tufts. Leaves long, linear, acute. Flowers pink and crimson with a dark eye, solitary, on long radical peduncles covered with small granular protuberances. South Africa.