The Latin word calculus means pebble and in this case probably refers to both the roundness and the firmness of the plant bodies.
These bodies are to 30 mm diameter, ball- to barrel-shaped, very firm, whitish-green to pale yellowish-green, without any markings; they form a hemisphere with age.
The flowers are open at night (sometimes staying open during cool mornings) and are said to smell strongly like cloves or carnations; they are golden yellow to deep reddish orange and appear in April-June.
The plants occur in full sun on salty quartz flats and gentle slopes in the Knersvlakte.
First picture taken 10th Sept. 2010; others 12th May 2017