Astrophytum ornatum, the bishop's cap or monk's hood cactus, is a flowering plant of the family Cactaceae, endemic to the Central Plateau of Mexico.

Solitary and cylindrical in form, it may grow up to 2 metres (6.6 ft) in height and 30 centimetres (12 in) in width on the Central Plateau.

It develops numerous white woolly flakes for protection from the sun.

It is a rugged plant resistant to root rot, and easy to grow in a well-drained soil.

Astrophytum ornatum has gained the Royal Horticultural Society's Award of Garden Merit.