Description
Astrophytum asterias var. nudum (a.k.a. cv. Ruri Kabuto) has a very characteristic glabrous stem lacking the white tufts of loose hairy scales typical of the common Astrophytum asterias. The smooth green epidermis show up the felty areoles.
Forma rubra (red form): The red schizochromic form (Astrophytum asterias var. nudum f. rubra) has bright orange-red stems due to the absence (or reduced production) of chlorophyll pigments: every other pigment is present at normal levels, the dominant green colouration is lost, but will still more than likely have normal other pigments that give the yellow overall appearance of the stem. This form with red stems is very attractive and highly prized. This schizochromic form is almost always seen grafted on stronger columnar species, and cannot can be grown on its own roots. However some clones have enough chlorophyll in their tissues and can be grown on they own roots too, but very slow growing.
Habit: It is usually solitary unless damaged.
Stem: bright orange to dark red, much depressed, disc-shaped to low dome-shaped (Only in cultivation plants may have a spherical till columnar shape, mature plants 2-7 cm tall, 5-16 cm broad, smooth completely flake free (without the minuscule tufts of bright white hairy scales).
Ribs: The stem is typically divided by very narrow but distinct vertical grooves into 8 broad ribs. The ribs are very low, almost flat on top, forming triangular sections with no cross-grooves.
Areoles: Round, prominent, 3-12 mm in diameters, forming a line up to the centre of each rib, felted to hairy, white till straw-coloured, then grey. Normally 3 to 10 mm apart.
Spines: Not any.
Flowers: Apical, diurnal, radial, 3-5 cm long, 5-7(-9) cm in diameter opening widely, yellow with orange/red throats.
Blooming season: Spring to summer and each flower lasts for one or two days only.
Origin and Habitat
Garden origin (Nursery produced cultivar)
Cultivation and Propagation
Variegated and albinos cacti are regarded as choice and difficult in cultivation, but despite that many of them are relatively easy to grow. But be aware that they cannot tolerate prolonged exposure to direct sun light (especially during the hottest summer days), so grow them in half-shade or under filtered sun. They are sometime seen as grafted plants, but many grow well on their own roots, too.
On the contrary, the albinos can survive only if grafted on a strong green base.
Use mineral well-permeable substratum with little organic matter (peat, humus). Water sparingly from March till October and keep perfectly dry in winter at temperatures from 5 to 15 degrees centigrade. (In general these plants are more tender and cannot endure freezing temperatures ) In the rest period no high atmospheric humidity!!
Propagation: Usually by seed. Plants are often grafted onto column-shaped cacti.
Bibliography
Major references and further lectures
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Edward Anderson “The Cactus family” Timber Press, Incorporated, 2001
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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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David R Hunt; Nigel P Taylor; Graham Charles; International Cactaceae Systematics Group. “The New Cactus Lexicon” dh books, 2006
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N. L. Britton, J. N. Rose: “The Cactaceae. Descriptions and Illustrations of Plants of the Cactus Family.” Volume III, The Carnegie Institution of Washington, Washington 1922
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Brian Loflin, Shirley Loflin “Texas Cacti: A Field Guide” Texas A&M University Press, 26/Oct/2009
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Albert Michael Powell, James F. Weedin “Cacti of the Trans-Pecos and Adjacent Areas” Texas Tech University Press, 2004
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Del Weniger “Cacti of Texas and Neighboring States: A Field Guide” University of Texas Press, 1984
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Alfred Richardson “Plants of Deep South Texas: A Field Guide to the Woody and Flowering Species” Texas A&M University Press, 2010
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Jackie M. Poole, William R. Carr, Dana M. Price “Rare Plants of Texas: A Field Guide” Texas A&M University Press, 2007