About 500 species of annuals, biennials, perennials and subshrubs from the northern hemisphere, the southern half of Africa and temperate South America. They vary greatly in habit from cushion or mat-forming to erect and sparingly branched. They have opposite pairs of usually simple and entire leaves and terminal cymes (sometimes solitary) of five-petalled flowers with tubular to greatly inflated calyces.
Among the smaller mountain species are several which are first rate and indispensable rock garden plants, e.g. S. acaulis and S. schafta. Many more are worthy of trial. Most of them require moist but freely draining soil and a moderately sunny site. Propagation by seed when ripe or in spring, division in autumn or early spring and cuttings in late spring or late summer.