Discocactus Pfeiff.

Greek diskos—disk, referring to the flattened stems.

Body mostly solitary, low-growing, flattened spherical to spherical. Stems spiny, the ribs distinct or tuberculate. Flowers nocturnal, arising from an apical, often sunken, woolly head (cephalium), white; summer. Flower tube narrow, scaly. Fruit mostly spherical to club-shaped, fleshy.

The 2 commonly cultivated species are keyed out below. D. placentiformis (Lehm.) K. Schum. from Brazil (Bahia) is generally known under its synonym D. bahiensis Britton & Rose while D. horstii Bruining & Brederoo from E Brazil is generally grown as a cristate form grafted onto other cacti.

Flowers nocturnal, fragrant, white, arising from a cephalium.

5-8 species from Brazil, E Bolivia and N Paraguay.

Taylor, N.P. (1981).

Source: Thompson, A, ; Forbes, S.; Spencer, R. (1997). Cactaceae. In: Spencer, R.. Horticultural Flora of South-eastern Australia. Volume 2. Flowering plants. Dicotyledons. Part 1. The identification of garden and cultivated plants. University of New South Wales Press.

kingdom Plantae
phylum   Tracheophyta
class    Magnoliopsida
superorder     Caryophyllanae
order      Caryophyllales
family       Cactaceae