Plants of this species are sparingly to densely branched (usually from the base) and form clusters up to 9 cm in diameter.
The columnar plant bodies are usually erect (rarely more or less flat on the ground); 20-90 mm long and 6-15 mm thick.
Flowering occurs from May to October; the flask-shaped flowers have cream, 9-11 mm long petals.
The species is found in the western part of Namaqualand from near Port Nolloth to the Vanrhynsdorp area, on exposed quartz gravel flats and gentle slopes, rarely on rocky outcrops and in shallow pans on rocks.
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
This very variable taxon occurs from southern Namibia to the Cederberg in South Africa, but mainly in the mountainous area of Namaqualand near Vanrhynsdorp, in rock crevices or between boulders, often in very exposed positions.
The plants form much-branched shrublets up to 0,5 m tall. The leaves are green, sometimes turning yellowish green or purplish red; they are almost triangular in section, usually 20-35 mm long (sometimes as short as 10 mm or as long as 50 mm) and 2-4 (sometimes 6) mm wide, about as thick as they are wide.
In autumn/early winter (March-June) the flowers appear, which as a rule are yellow-green, rarely white with a pink tinge.
No less than 25 synoniems have been recorded for this species, so it will come as no surprise that it is quite variable.
As a rule, the plants consist of only one pair of leaves, rarely 2 or 3. These leaf-pairs are 20-50 mm long and 15-30 mm wide, sunken into the ground. Old leaves stay on the plants for 1 or 2 years.
The flowers appear in April – June; they are 20-50 mm in diameter and may be white, pink, red , magenta, or yellow (see part 2). Even within one population one can come across all these colours.
The plants are locally abundant on flats or slopes rich in quartz pebbles in the Vanrhynsdorp area.
The first 3 pictures were taken on 30 March 2012, # 4 early next morning. Last one: 3 Sept. 2010
Earlier this month I was on an 8-day trip to Namaqualand with a couple of friends, hoping to see Argyrodermas and Conophytums in flower.
In spite of the drought we saw a lot of interesting plants, a few of which are pictured below.
Many other pictures should find their way into posts on succulents from the area.