Erect, spreading, loosely-branched shrubs, rarely cushion-like or small trees, to 5 m high. Roots ± tuberous. Stems with indefinite growth, sometimes divided into segments, cylindric to somewhat clavate, distinctly tuberculate; tubercles elongate to ovate-rhomboid, slightly raised and rib-like, sometimes mamillate. Leaves restricted to young developing stem-segments and on young pericarpels and hypanthia, rudimentary, caducous, terete, ± subulate. Areoles terminal on tubercles, elongated, slightly depressed or raised, invested with glochids, white or light yellow woolly hairs, and spines. Spines 1–10, acicular or subulate, smooth, lacking a papery sheath. Glochids few and often absent, white to light yellow. Flowers lateral or sometimes terminal, bisexual, regular. Perianth caducous, segments numerous, spreading to erect, virtually free, inserted on hypanthium apex; outer tepals forming a distinctive red-pink cap at bud stage; inner tepals pink to red, erect or slightly spreading. Stamens inserted in numerous rows. Ovary inferior; style thick, with 5 stigmas. Fruit succulent, ovoid to obovoid or obloid, tuberculate, solitary or forming short chains of up to 4 by proliferation, with glochidiate areoles and sometimes spines, green to yellowish; seeds subglobose to irregularly angular, or pyriform, with smooth to slightly rugose funicular envelopes covered with fine hairs, and a rudimentary funicular girdle.
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