Perennials, often shrubby or tree-like; roots fibrous, rarely tuberous. Leaves rosetted or distichous, linear to ovate-lanceolate, succulent, glabrous to spiny, margins serrate-dentate, usually spiny. Inflorescence axillary, racemose, spicate or capitate, usually many-flowered, branched or unbranched. Flowers bisexual, subtended by bracts, slightly zygomorphic, usually pedicellate; perianth segments in two series, free or united, swollen above the ovary; stamens 6, usually exserted; style filiform, exceeding anthers, stigma usually capitate. Fruit a loculicidal capsule; seeds triquetrous to flattened, sometimes winged.
About 340 species in Africa, Madagascar and Arabia, widely cultivated as ornamentals; 7 naturalised in Australia, 2 naturalised in Victoria.