This remarkable cactus was originally described as the sole member of the genus Digitostigma and it is still often referred to under that name.
Astrophytum caput-medusae grows in low elevation habitats between 100 and 200m in flat terrain with thorny scrub in the Mexican state of Nuevo Leon. The plants are found growing at the base of bushes with grasses and other small plants and can be quite difficult to spot. During the one time in habitat I observed this plant I only saw three specimens although I am sure many more must exist. Other cacti in the vicinity include Echinocereus (Wilcoxia) poselgeri and Sclerocactus (Ancistrocactus) scheeri.
Fig. 1 A. caput-medusae in habitat
Astrophytum caput-medusae has a large taproot with a crown of long but thin tubercles that can grow up to 20cm long but less than 5mm in diameter. The epidermis is brownish in colour and has the white flecking that is a unique feature of Astrophytum. At the end of each tubercle is a small areole where sometimes a small spine cluster is present. The flowers emerge from a second larger areole part way down the tubercle. They are very characteristic of Astrophytum in form with yellow petals and a red throat.
In cultivation the seedlings grow quickly and at just a few weeks old the first distinctive tubercle forms. As with any cacti with large tuberous roots cultivation can be tricky and a well drained compost with careful watering is required. Plants are often seen grafted, where they can grow to much larger proportions than is natural. During the winter months the tubercles of Astrophytum caput-medusae are liable to dry up and a little water can be given but only if temperatures are kept reasonably high, 10-15C. With luck flowers will be seen in the third or fourth year and maybe earlier if grafted.
Fig. 2 A caput-medusae in cultivation
They are generally easy plants to grow and will live in a cool greenhouse (mine runs at a minimum of 5°C) in a sunny position. I have had another seedling flower while in a 2 3/4” pot. Why not try this wonderful plant in your own collections – it really brightens up the winter months.
Fig. 3 A caput-medusae seedlings
Paul Hoxey
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