Soil

Mini grey-green globular plant covered w/soft white spines. Readily clumping

M. standleyi

Slow to form clumps, 3 to 4 ft across. Globose stems to 6″. Prominent conical tubercles. Yellowish flowers.

8″d. Clumping w/prominent tubercles, some axil wool

Generally forms clumps, to 2″d./6″h.; tubular red flowers

Medium sized solitary plants, pyramidal stems; long radial spines

M. celsiana

Usually solitary, globose to 6″. Variable spines. Carmine red flowers.

Solitary, cylindrical, to 4″d./6″h.; short twisted spines

Slow branching; to 6″ cylindrical; woolly between spines

12″h. clumps develop as stems divide

Green stems to 6″, variable spines; generally solitary

Green stems to 6″, generally solitary. Purple flowers. Thin yellow-brown spines.

M. calacantha

Slowly clumping, 4″ dia., 12″ tall

Occasionally branches; 4″d./12″h.; long curved yellow/brown spines. Blooms spring to fall with flowers that are a deep-pink to a purple color.

Small stems 2″ across x 4″ tall will form large clusters. Soft spines splay outwards. Creamy yellow flowers in summer and fall. Regular water in summer, keep dry in winter.

6″ round stems with lots of very white spines, with longer hooked spines. Large red flowers.

Small clumps of fast-growing cylindrical branches to 4″h. Purple-pink tubular blooms

Cylindrical stems 2″ around to 20″ long, some bristles. Lots of red spines along the crown of the plant.

Cylindrical stems 2″ around to 20″ long, some bristles