Description
The standard Mammillaria rodantha is a columnar cactus that characteristically divide dichotomously with age forming large clumps.
Crested form: This is a nice crested plant particularly appreciated by collector for its free blooming habit. It can form large tangled, brain like mounds in few years.
Stem: Fan shaped, dark green, usually 15-40 cm in height and up 8-10(13) cm in diameter. White wool can be seen growing on the top part of the plant body.
Tubercles: Conical to cylindrical, without latex.
Axils: With fine bristles.
Central spines: About 4 to 6 straight or more or less curved up to 1,5 cm long, vividly coloured reddish-brown but also straw-coloured or golden yellow. The bottom half of the cactus has spines that are white or grey and appear to be dying.
Radial spines: Approximately 16 to 24, 3-10 mm long, glossy-white or yellowish.
Flower: Deep-pink to a purple colour, 20-23 mm long and 15-18 mm in diameter, stigmas usually purple.
Blooming season: The species flowers for very long periods of time. It starts blooming in the spring and continues to bloom until summer, but some plant will produce another ring of flowers in late October or even November.
Fruit: 15-25 mm long. Cylindrical to club shaped, purplish-pink frequently greenish at the base.
Seed: Brown to orange-brown.
Origin and Habitat
Garden origin (Nursery produced selection)
Cultivation and Propagation
This is an easy to grow cultivar, just as a classic cactus, don’t requires any special treatment. It is sometime seen as a grafted plant but grows very well on its own roots too.
Soil: Use mineral well permeable mineral soil with little organic matter (peat, humus).
Exposure: They need a good amount of light shade to full sun this help to keep the plants healthy, although slow growth.
Watering: Water sparingly from March till October (weekly during summertime, if the weather is sunny enough) , with a little fertilizer added. Less or no water during cold winter months, or when night temperatures remain below 10° to prevent root loss. It is sensitive to overwatering (rot prone).
Fertilization: Feeding may not be necessary at all if the compost is fresh then, feed in summer only if the plant hasn’t been repotted recently. Do not feed the plants from September onwards as this can cause lush growth which can be fatal during the darker cold months.
Hardiness: Keep perfectly dry in winter at temperatures from 5 to 15 degrees centigrade. (but it is relatively cold resistant and hardy to -5° C, or possibly colder for short periods) In the rest period no high atmospheric humidity!! (Temperature Zone: USDA 9-11)
Crested growth: Unlike ‘monstrose’ varieties of plants, where the variation from normal growth is due to genetic mutation, crested growth can occur on normal plants. Sometimes it’s due to variances in light intensity, or damage, but generally the causes are unknown. A crested plant may have some areas growing normally, and a cresting plant that looks like a brain, may revert to normal growth for no apparent reason. If you have any of the crested part left you need to remove the normal growth and leave the crested part behind this will need to be done regularly.
Propagation: Grafting or cuttings. Plants are usually grafted onto column-shaped cacti but proved to be able to produce their own roots if degrafted. Cuttings will take root in a minimum temperature of 20° C (but better in hot weather). Cuttings of healthy shoots can be taken in the spring and summer. Cut the stem with a sharp, sterile knife, leave the cutting in a warm, dry place for a week or weeks (depending on how thick the cutting is) until a callus forms over the wound. Once the callus forms, the cutting may be inserted in a container filled with firmed cactus potting mix topped with a surface layer of coarse grit. They should be placed in the coarse grit only; this prevents the cut end from becoming too wet and allows the roots to penetrate the rich compost underneath. The cuttings should root in 2 to 6 weeks. Large crested piece must be placed on the soil surface without burying the plant base down in the soil.
Bibliography
Major references and further lectures
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David Hunt, Nigel Taylor “The New Cactus Lexicon” DH Books, 2006
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John Pilbeam (1999) “Mammillaria The Cactus File Handbook” Nuffield Press.
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Stuart Max Walters “The European Garden Flora: Dicotyledons (Part I)” Cambridge University Press, 1989
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Edward F. Anderson “The Cactus Family” Timber Press, 2001
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