Description
Astrophytum myriostigma is a quite variable species and several breeds do exist. The “Irregular Ribs” is a rare form sought after for its unusual irregular, broken or branched ribs. In all other characteristics, namely size and shape of stems, flowers, fruits, roots etc. it is very similar to the standard species. Every plant is different and particular, and the form and shape of ribs varies with time.
Habit: It is a spineless succulent plant, usually solitary or with very few basal branches. A transverse section of the stem reveal a perfect star shaped form (like the common star-fish).
Stem: Globular to cylindric up to 60(-100) cm tall and 10-20 cm in diameter, bright green, covered with many minute white hairy scales that give it a characteristic chalk-white or silvery-grey appearance, but sometime naked. The scales are composed of very fine interwoven hairs, which, under a microscope, are very pretty object.
Roots: Fine, fibrous.
Areoles: Closed together
Spines: Wanting.
Ribs: Usually 5, slightly spiralling, regular, deep, prominent, very broad and acute.
Flowers: Funnelform, 4-7 cm long glossy yellow and sweet scented from the areole at the tip of the stem on mature plant. Outer perianth segments narrow, with brown scarious tips. Inner perianth segments numerous, oblong yellow with a silky shine. Scales on ovary tube scaroious, imbricated, very narrow often bristly tipped, with long wool in their axil.
Blooming season: Flowers appear intermittently throughout the warm months from April to September. Plants may take up to six years to flower.
Fruit: 2-2,5 cm in diameter, greenish to tannish-red, covered with brown, overlapping scales, with long wool in their axil.
Seeds: Dark brown, helmet-shaped, shining, with a large depressed hilum, the margins being turned in.
Origin and Habitat
Garden origin (Nursery produced cultivar)
Cultivation and Propagation
Astrophytum myriostigma is a summer grower species relatively easy to grow. It is sometime seen as a grafted plant but grows very well on its own roots too.
Growth rate: It is a slow growing and easily flowering species.
Soil: Use mineral well permeable substratum with little organic matter (peat, humus), plants may become too elongated if compost is too rich.
Repotting: Re-pot every 2 years. Use pot with good drainage.
Fertilization: It grows much faster with a low nitrogen content fertilizer in spring and summer. Potassium helps maintaining the plants compact and healthy.
Watering: Requires careful watering to keep plant compact. Water sparingly from March till October, the thin, fibrous roots suffer if there is humidity, therefore the plant should be watered only when the surrounding terrain is dry. Keep dry as soon as the temperature starts dropping in October and keep it perfectly dry in winter at temperatures from 5 to 15 degrees centigrade.
Hardiness: They need to be kept in a cool place during winter rest and are somewhat resistant to frost if kept on the dry side prior to, and during, cold weather (due to the altitude they are hardy to -5 C ° C, or less for short periods). Although it is one of the easier Astrophytum to grow, it tends to rot in winter during the resting phase, if kept wet. In the rest period no high atmospheric humidity!!
Sun Exposure: Light shade to full sun, its colour tends to richer and darker when grown in light shade.
Uses: It is an excellent plant for container growing. It always looks good and stays small.
Pests & diseases: It may be attractive to a variety of insects, but plants in good condition should be nearly pest-free, particularly if they are grown in a mineral potting-mix, with good exposure and ventilation. Nonetheless, there are several pests to watch for:
- Red spiders: Red spiders may be effectively rubbed up by watering the infested plants from above.
- Mealy bugs: Mealy bugs occasionally develop aerial into the new growth among the wool with disfiguring results, but the worst types develop underground on the roots and are invisible except by their effects.
- Scales: Scales are rarely a problem.
- Rot: Rot is only a minor problem with cacti if the plants are watered and “aired” correctly. If they are not, fungicides won’t help all that much. To prevent rottenness it is also advisable to surround its root neck by very rough sand or grit, this help a fast water drainage.
Propagation: Almost exclusively by seed. Plants are sometimes grafted onto column-shaped cacti. Cutting scions from a flourishing plant is almost a crime because the scions do not root easily.
Remarks: This quite variable plant has been widely grown for years and is now available in several cultivated variety and several breeds do exist. The famouse “Onzuka” is only one of these and though maybe the most beautiful, but a lot of other forms are represented in many collections.
Bibliography
Major references and further lectures
1)James Cullen, Sabina G. Knees, H. Suzanne Cubey “The European Garden Flora Flowering Plants: A Manual for the Identification of Plants Cultivated in Europe, Both Out-of-Doors and Under Glass” Cambridge University Press, 11/Aug./2011
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Edward F. Anderson “Das große Kakteen-Lexikon.” Eugen Ulmer KG, Stuttgart 2005
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Keith Grantham, Paul Klaassen “The plantfinder’s guide to cacti & other succulents” Timber Press, 18/mag/1999
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Britton & Rose “The Cactaceae” 4: 273, 1923
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Hiroshi Hirao “Colour encyclopaedia of cacti” Japan 1979 (Japanese language and script)
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Willy Cullmann, Erich Götz (Dozent Dr.), Gerhard Gröner “The encyclopedia of cacti” Portland, OR: Timber Press, 1986
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David Hunt, Nigel Taylor “The New Cactus Lexicon” DH Books, 2006
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Curt Backeberg “Cactus Lexicon” Sterling Publishing Company, Incorporated, 1978
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Del Weniger “Cacti of the Southwest: Texas, New Mexico, Oklahoma, Arkansas, and Louisiana” University of Texas Press, 1969
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Del Weniger “Cacti of Texas and Neighboring States: A Field Guide” University of Texas Press, 1984