Astrophytum ornatum

Astrophytum ornatum.

Synonyms include Echinocactus mirbelii.

This is the largest of the species.
Young plants are spherical and the older ones more cylindrical and up to around 1 m high.
Up to 30 cm across they have 8 (5 – 10) prominent, narrow ribs.
Areoles, down the apex of the ribs, have short, woolly yellowish-white hairs that fall off.
There are clusters of up to 11 straight spines in the areoles.
They are up to 4 cm long apart from a longer central one.
Initially yellowish they age to brown then grey.

The dark or grey-green stems are patterned with white or yellowish spots of scales.
These run in horizontal bands across the ribs.
They vary greatly with some plants having none to others with dense scales.

The bright yellow flowers appear at the top of the plant.
They are up to 12 cm across and the very hairy hypanthium (tube) is short.

Astrophytum ornatum var. mirbelii.
Some recognise this as a variety while others believe it is just part of the natural variability of the species.
It differs from A. ornatum by having the white flecks evenly distributed over the surface rather than in bands.