Description
Rebutia pygmaea var. pygmaea (sensu stricto) based on the description of Britton & Rose 1922:
Stem: Simple, ovoid to short-cylindric, 1 to 3 cm. long, 1.2 to 2 cm. in diameter, or sometimes branched with 2 to many short joints from a much thickened root; tubercles small, more or less arranged into 8 to 12 spiraled rows; areoles narrow, somewhat lanate.
Spines: All radial, 9 to 11, short, appressed, 2 to 3 mm long, acicular, somewhat swollen at base.
Flowers: From the lower part of the plant, somewhat curved at base, becoming nearly erect, 18 to 25 mm. long, rose-purple; scales on ovary and flower-tube small, hairy in their axils.
Fruit: Globular, 6 mm. in diameter.
Origin and Habitat
Bolivia and northwestern Argentina.
Type locality: Yavi, province of Jujuy, Argentina.
Cultivation and Propagation
Rebutia pygmaea is a summer grower species that is easy to cultivate and recommended for beginners. The whole Rebutia pygmaea complex has delightful flowers and the plants remain compact, and clumps can easily be managed by division. Another advantage is that the plants are very cold hardy in Winter if kept dry.
Growth rate: It is a slow growing but easily flowering species that will make clumps given the best conditions.
Soils: It likes very porous standard cactus mix soil with a pH slightly on the acidic side.
Repotting: This species will occupy a small flower pot comfortably and remain a manageable sized house plant, repotting should be done every other year or when the it has outgrown its pot. Use pot with good drainage.
Watering: Needs moderate to copious waterings in summer, but do not overwater (the root system is rot prone) and allow the pot to dry out between waterings. Keep dry in winter at a minimum temperature of 0°C.
Fertilization: Feed with a high potassium fertilizer in summer.
Hardiness: It is reputedly resistant to frost if kept on the dry side prior to, and during, cold weather and requires a winter rest period (hardy to -12 C ° C, or less for short periods), but for safe cultivation it is best to avoid freezing temperatures. It does not like high temperatures in summer, and will be perfectly happy in pots outdoors from April to September if protected from torrential rain and hail
Exposition: The plant tolerates extremely bright situations but enjoys filtered sunlight or afternoon shade, inside it needs bright light, and some direct sun. Tends to bronze in strong light, which encourages flowering and heavy spine production, but is likely to suffer from sun scorch or stunted growth if over exposed to direct sunlight during the hottest part of the day in summer.
Uses: It is an excellent plant for container growing. It always looks good and stays small. It look fine in a cold greenhouse and frame or outdoor in a rockery.
Pests & diseases: It may be attractive to and liable to damage by spider mites and thrips
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.
Rot: This species is particularly easy and accommodating, seldom suffer of cryptogamic diseases. Rot it is only a minor problem with rebutias if the plants are watered and “aired” correctly. If they are not, fungicides won’t help all that much.
Propagation: Division, direct sow after last frost. Seeds germinate in 7-14 days at 21-27° C in spring, remove gradually the glass cover as soon the plants will be well rooted (ca 1-2 weeks) and keep ventilated, no full sun for young plants! To make a cutting twist off a branch and permit it to dry out a couple of weeks, lay it on the soil and insert the stem end partially into the soil. Try to keep the cutting somewhat upright so that the roots are able to grow downward.
Note: It would appear that in cultivation they grow larger and cluster more vigorously than in habitat.
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 4, The Carnegie Institution of Washington, Washington 1923
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Curt Backeberg “Die Cactaceae: Handbuch der Kakteenkunde” Gustav Fischer Verlag, Stuttgart New York 1982–1985
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Backeberg, Curt, “Das Kakteenlexikon” p. 271, 1966
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Mosti, Stefano; “Digitorebutia” Buining & Donald (2), Cactus & Co., 4: 87, 2000
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Pilbeam, John; “Rebutia” p. 73, 1997
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Rausch Walter, “Lobivia ‘95”, p. 109, 1986
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Ritter, Friedrich; “Kakteen in Südamerika”, 2: 616, 1980
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Šída Otakar, “Rod Rebutia”, p. 85, 1997
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Šída, Otakar; “Atlas kaktus?”, tab. 29, 2002