This section is from the book "The Standard Cyclopedia Of Horticulture Vol2", by L. H. Bailey. See also: Western Garden Book: More than 8,000 Plants - The Right Plants for Your Climate - Tips from Western Garden Experts.
(classical name; said by Pliny to be in honor of King Juba's physician; possibly from the Greek for fat). Euphorbiaceae. Milkweed (improperly) Wolfs-milk. Spurge. The last name, most often applied to the genus as a whole, belongs more properly to the common herbaceous species and especially to E. Lathyris. Of very diverse habit, from succulent cactuslike trees to low or prostrate herbaceous weeds; planted mostly in the open, but some kinds grown under glass as oddities and some as florist's plants.
The genus is characterized by the single pedicellate, pistilate flower without floral envelopes, or with only a rudimentary calyx, surrounded by numerous staminate flowers, each consisting of a single stamen separated from its pedicel only by a joint; the whole infloresence surrounded by a more or less cup-shaped involucre with 5 lobes and 1-5 glands is called a cyathium. The involucre is regular or nearly so; the glands free from one another: the fruit an explosive caps., with 3 carunculate seeds; the staminate flowers are usually subtended by minute bracts. - One of the largest plant genera, of not less than 700 and probably over 1,000 species, occurring in most temperate and tropical regions. Many are desert plants and the greater number grow in dry and sterile places. Euphorbia is distinguished from the nearest related genera, Pedilanthus and Synadenium, by its regular or nearly regular involucre, which in Pedilanthus is protuberant on one side of the base and contains the glands, and by the free involucral glands which in Synadenium are united into a ring.
Some of the fleshy species are very similar to succulent cacti and Asclepiadaceae. One long grown under the name of E. pendula, Boiss., is a Sarcostemma according to N. E. Brown. For E. tithymaloides, see Pedilanthus; for E. Grantii, Hort., and E. arborea, Hort., see Synadenium.
Monographed by Boissier in DeCandolle's Prodromus, 15, pt. 2 (1862). See local floras and Norton, Rept. Mo. Bot. Gard. 11, for native species. See also Fobe, in Monatsschrift fur Kakteenkunde, 8:42 (1898) and Berger, Sukkulente Euphorbien, a manual of the cactus-like species in cultivation. The recent work of N. E. Brown of Kew in Flora of Tropical Africa and Flora Capensis describes and gives keys to practically all the African species, which include nearly all the succulent ones, both wild and cultivated. Although the vegetative form varies remarkably, so that the various sections of the genus are considered of generic rank by many authors, the floral characters are very similar and so inconspicuous as to be of little importance generally in a horticultural work.
Most of the species have abundant milky juice, and the cactiform kinds have been thus distinguished from cacti, but many cacti also have milky juice. The juice of many species is acrid-poisonous, especially if it comes in contact with mucous membranes or open sores. The juice from some of the species is used in medicine as a purgative.
Many of the fleshy species are cultivated by lovers of succulents for their curious shapes; and a few are valuable for their ornamental foliage. The flowers are usually too minute to be noticeable. Some, like E. corollata (Fig. 1437), E. maculata, E. Cyparissias and E. margi-nata, are weeds in America, but not troublesome. The great majority of the species are insignificant herbs. The species are remarkably free from injurious insects, and are rarely attacked by a few fungi.
The fleshy species are grown much the same as cacti, but the culture is less difficult, and they do well with warmer treatment. In winter they are kept in a dry and cool house, 50° to 55° F., with good light and little water. Drips must be carefully avoided. In summer the pots should be plunged outdoors in hot dry situations, with a moderate supply of water and especially good drainage. It is better to protect them from continued rain, but most species do well without this. The more fleshy species, like E. Caput-Medusae, E. mammillaris, and E. meloformis, require more heat and better care than the others. They have to be watered with great care in winter. The air of most greenhouses is too damp for them if the requisite low temperature is maintained. The winter conditions of air and temperature in ordinary living - rooms make them ideal for the succulent euphorbias. Species like E. neriifolia need water in the growing season and dry conditions after the leaves fall. The shrubby species, like E. atropurpurea and E. dendroides, do well with the treatment of the more fleshy kinds.
See D. A. W. and F. S. Curtis, in Sharon Cactus Guide, March and May, 1897.
Fig. 1437. Cyathium of Euphorbia corollata ( X 2). The pistillate flower is at 8, surrounded by several staminate flowers arising above the involucral glands with their five oblong spreading petaloid appendages. No. 3.
The few hardy species of ornamental value make good border plants or are suitable for the rockery. E. epithymoides usually known in gardens as E. polychroma, is one of the best herbaceous perennials, forming a hemispherical clump with beautiful yellow foliage of different shades when in bloom. E. palustris and related species are similar but erect and not compact.
The succulent species can nearly all be propagated by cuttings. These are taken best in early summer, allowed to dry somewhat and then planted in sand, charcoal or a mixture of these. Coal-ashes are used effectively by some. When seeds can be procured, they may be used in propagation. Grafting, as is sometimes practised with cacti, is possible. Potting soil need not be rich. A coarse sandy loam, or, some say, any kind of soil will do.