Spiny green cactus with variable white spots from north-central Mexico. Globose to cylindrical stems grow up to 6-12 inches in diameter. Spines are yellow, turning brown or gray with age, with 1 central and 5-10 radials. Flowers are large and yellow. Fruit is scaly and hairy.

May be distinguished from the similar but generally smaller A. capricorne based on flower color (all yellow instead of yellow with a red center), spines (less curved or twisted, thicker, with a central spine), and origin (on the southern slopes of the Sierra Gorda or in Cuatro Ciénegas, not further north or east of those respective locations). Young plants of the two species may be very difficult to tell apart, but ornatum seems to be more common in cultivation.

Found in Querétaro and Hidalgo.

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Most often the plant has 8 ribs, and sometimes the ribs spiral.
Areoles have 5-11 spines. It is cold resistant to low to mid 20F.
It is found in limited area in Mexico, in semi-desert, only in 10 locations - so is considered vulnerable, due to diminishing area of habitat and illegal collection of plants.

It is found often growing on rocks in canyons and can reach a height of 3'-4' in the wild.

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