SAXIFRAGACEAE, in botany, a small family of dicotyle dons belonging to the sub-class Archichlamydeae and the cohort Rosales. There are ninety genera with about 75o species dis tributed through the Arctic and north temperate zone, often alpine. It is represented in Britain by its largest genus Saxifraga (see SAXIFRAGE), Clirysospleniurn (golden saxifrage) and Parnassia (grass of Parnassus). The plants are herbs, generally with scat tered exstipulate leaves with a broad leaf-base. The small flowers are generally arranged in cymose inflorescences and are bisexual, regular and hypogynous, perigynous or more frequently more or less epigynous, this variation in the relative position of the ovary occurring in one and the same genus Saxifraga. The free stamens are obdiplostemonous, i.e., those of the outer whorl are opposite to the petals, and two carpels. The carpels are sometimes free, more generally united at the base, or sometimes completely joined to form a one- or two-chambered ovary with two free styles. The fruit is a many-seeded capsule.
Nearly half the species (35o) are contained in the genus Saxi fraga. Chrysosplenium, with 45 species, two of which are British, has a very similar distribution. The North American genus Heuchera has sometimes apetalous flowers. Astilbe has 20 species in temperate Asia and north-eastern North America; A. japonica
is commonly grown in the spring as a pot-plant, and often mis named Spiraea.
The family is now extended to include other groups of genera differing in habit and more or less in general conformation from those referred to. Among these is the genus Ribes. to which belong the gooseberry (R. Grossularia) and currants of gardens. These are shrubs with racemes of flowers which have only one whorl of stamens (isostemonous), an inferior unilocular ovary with two parietal placentas, and fruit a berry. Other genera are Hydrangea (q.v.), Deutzia and Philadelphus, all well-known garden plants; P. coronaries is the so-called syringa or mock-orange. They are shrubs or trees with simple generally opposite leaves, pentamerous flowers with epigynous stamens and a tri- to pentalocular ovary. Escallonia, which represents a small group of genera with leathery gland-dotted leaves, is also included.
In North America, Saxifraga is represented by about 3o species, the other prominent genera being Ribes (currant and gooseberry) with 20 species, and Heuchera (alum root) with to species.
For further details see A. Engler and K. Prantl, Die Natiirlichen Pflanzenfamilien (Leipzig, 1887-1908) ; A. B. Rendle, Classification of Flowering Plants (Cambridge, 1925).