Saxifragaceæ, a natural order of exogenous plants, comprising herbs, shrubs, and trees, so varied in character that botanists are not in agreement respecting its limits. The British genera, of which there are four, all of which are herbs, are very diverse in character, yet they give very little idea of the range of the variation of generic character in the order when they are compared with the ligneous or arborescent exotic genera. They are all, however, distinguished from the genera of the closely allied orders by their regular flowers; four, five, or rarely ten-lobed calyx, more or less adherent to the ovary; petals equal in number to segments of calyx or wanting; stamens also generally equal in number or twice as many, still more rarely indefinite in number; ovary either adherent or inserted in a broad base, either two or four celled, or, if one-celled, having two or more parietal placentas often lobed at the top, with the same number of styles or stigmas as cells or placentas, rarely twice as many; fruit a capsule, with several seeds, usually many to each cell or placentas; the albumen usually copious. The family is spread over nearly the whole world, most numerously in the mountainous regions of the northern hemisphere; they are rare in tropical America, in Peru and Java, and in southern Australia. The prevailing property is astringency. The small grain-like roots of Saxifraga granulata, a native of Britain and other temperate countries of Europe, were formerly reputed to be efficacious in calculus. S. tridactylites, also a native of Britain, is said to be beneficial in diseases of the liver. But the only species of the numerous herbaceous class having any well-based reputation for medicinal or official virtues is the Alum-root (Heuchera americana), which is abundantly distributed in rocky and shady places throughout the United States. The root, which is intensely astringent, is employed by the Indians to heal wounds and persistent ulcers, and it is said to form the basis of a powder reputed in America to be a cure for cancer.
Among the arborescent species there are some which produce valuable timber. Cunonia capensis is the Red Alder or Rood Els of the Cape of Good Hope. Its timber resembles that of the lime-tree, but is more tough and close-grained, and being also susceptible of a fine polish is valued alike for agricultural purposes and for cabinet-work. Platylophus trifoliatus is the White Alder or Wit Els of the same country; it is a larger growing tree than the preceding, the trunk often attaining a diameter of 3 or 4 feet. The wood is white, light, and comparatively soft, and is valued for making boxes, drawers, the more common articles of furniture, picture-frames, and the like. The bark of some of the species of Weinmannia are employed in Peru and in the West Indian Islands in the tanning of leather, and also for adulterating Peruvian bark. Some of the Australian species yield gum. The Hydrangea, so popular in British gardens and in cottage windows, belongs to this family.