Aylostera (Rebutia) walteri was first described by Prof. Dr. Lothar Diers in Kakteen und andere Sukkulenten 40(8): pp. 186-90, in 1989, the journal of the Deutsche Kakteen-Gesellschaft.

The description is extensive, in Latin and German with further notes in German. Here is the text of the description of this species in the original Latin, with a summary of the additional notes, but you should look up the original description for more details, including colour and black-and-white photographs and drawings, and scanning electron microscope photographs. The English translation below is my own.

Rebutia (Aylostera) walteri Diers spec. nov.

Corpus solitarium, raro paulum proliferans, ± applanate globosum; in natura 1,5-2 cm, in cultura ad er. 5 cm diam., atroviride; radix ramosa, non rapiformis. Costae 15-22, plerumque ± spiraliter decurrunt, solutae in tuberculis parvis. Tubercula 1-2 mm alta, in basi eorum (5-) 6 angulata, er. 5 mm longa et er. 4 mm lata. Areolae circulares ad ± ovales, er. 1 mm diam., tomento sufflavoalbo, deinde clarogriseo-griseo. Spinae plerumque 15-22, tenues, patentes, er. 3 mm longae, in cultura ad 18 mm longae; exteriores subalbae acuminibus brunneis, interiores brunneae acuminibus atrioribus; spinae longissimae in parte superiore areolae.

Flores 3-4 cm longi, ad 5 cm lati, late infundibuliformes. Pericarpellum globosum-ovale, 4-5 mm longum, er. 3,7-5,3 mm latum, sufflavum-clarosubbrunneum-subviride, interdum claroroseum; 9-13 squamis ± lanceolatis, 1-1,5 mm longis et er. 0,3-0,4 mm latis; in axillis earum 0-4 pili setiformes ad 5 mm longi et complures pili tenues crispati. Receptaculum 10-15 mm longum; eius pars intima est zona 2,3-5,7 mm longa ubi stylus est concretus cum floris tubo, supra ea tubus angustus qui in faucem abrupte dilatatus infundibuliforme; flavoviride-claro-brunneum- claroviolaceoroseum; 3-5 squamis acutolanceolatis ad ± triangularibus sufflavis-subbrunneis-clarogriseis-subrubris in partibus inferioribus receptaculi. In axillis squamarum 0-5 pili setiformes ad 11 mm longi et complures pili tenues crispati.

3-6 folia transeuntia ± lanceolata; pars dorsalis eorum sufflava-aurantiaca, pars ventralis aurantiaca-violaceosubrubra aut claroviolaceosubrubra cum marginibus clarioribus ad claroaurantiacis. Folia perianthii exteriora 15-23 mm longa, 4,7-7 mm lata, longeovalia-lateovalia, acuminata, sufflava-aurantiaca cum partibus centralibus longitudinalibus violaceoroseis-violaceosubrubris. Folia perianthii interiora 15-21 mm longa, 5- 6,5 mm lata, ± longeovalia-lateovalia, interdum in acuminibus irregulariter incisa, aurantiaca aut aurantiaca cum acumine et partibus centralibus longitudinalibus violaceoroseis. Omniafolia perianthii 16-18. Camera nectarea alba, ± tubularis, 5-8 mm longa; in parte inferiore 0,6-0,8 mm lata, in parte superiore 1,4-2,3 mm lata. Nectarium er. 1,2 mm latum summa in camera nectarea. Omnia stamina 55-65. Stamina infima inserta paulum supra nectarium, stamina suprema in basi foliorum perianthii interiorum vel paulum sub basi eorum. Inter stamina intima et suprema pauca stamina dispersim inserta. Stamina intima 6,5- 7 mm longa; stamina in faucem receptaculi longiora, stamina suprema 8-10 mm longa. Omnia filamenta alba, ± cylindracea. Antherae sufflavae, er. 0,9-1,1 mm longae, er. 0,5-0,6 mm latae.

Fructus ± globosus, er. 4-6 mm diam., ± viridis squamis subvi- ridibus, denique griseus, siccariens; in axillis squamarum pilo- sitas pericarpelli manet; continens 35-72 semina. Semen 1,1- 1,3 mm longum, 0,8-0,9 mm latum; ± olliforme (sensu Buxbaum), interdum parva crista in parte ventrali.

Regio hili basalis, ± ovalis, vix vel paulum demersa, continet cicatricem funiculi et zonam micropylae quae perspicue procedit; regio hili saepe residuis texturae subalbis-subbrunneis tecta est. Testa opaca subbrunnea-nigra, cellulis paulum convexis, raro planis, tunica arillosa (sensu Buxbaum) decidiens, particula tunicae adhaerentes.

Habitat in Santa Victoria, Salta, Argentina, in altitudine 2500- 2700 m.

Holotypus in Herbario Universitatis Coloniae (KO- ELN), Germania sub nr. Hoffm. 1960A.

English translation

Rebutia (Aylostera) walteri Diers spec.nov.

Single bodied, rarely proliferating, more or less flattened spherical; in habitat, 1.5 – 2cm, in cultivation up to 5cm in diameter, dark green; roots spreading, with no tap root. 15 – 22 ribs, more or less spiraling, divided into tubercles. Tubercles 1 – 2mm high, 5 or 6-sided at the base, 5mm long and 4mm wide. Areoles circular to more or less oval, 1mm in diameter, with whitish wool, later light grey. Generally 15 – 22 spines, thin, spreading, 3mm long, in cultivation up to 18mm long; outer spines whitish with brown tips, inner spines brown with black tips; spines above the areoles longer than others.

Flowers 3 – 4cm long and 5cm wide, broad funnel-shaped. Pericarpel spherical to oval, 4 – 5mm long, 3.7 – 5.3mm wide, yellowish to light brown to greenish, sometimes light pink; 9 – 13 lanceolate scales, 1 – 1.5mm long and 0.3 – 0.4mm wide; with 0 – 4 bristles up to 5mm long and several thin curly hairs in the axils. Receptacle 10 – 15mm long, the lowest part 2.3 – 5.7mm long and fused with the style; above it the tube is narrow but abruptly change to a wide funnel; yellowish-green to light brown to light purplish pink; 3 – 5 sharply pointed triangular scales in the lower part of the receptacle, yellowish-brownish-light grey-reddish. 0 – 5 bristles up to 11mm long and a few curly hairs in the axils of the scales.

3 – 6 more or less lanceolate transient tepals; outer parts yellowish-orange, inner parts orange-purplish red or light purplish red with lighter to light orange edges. Outer petals 15 – 23mm long, 4.7 – 7mm wide, long-oval-broad-oval, pointed-tipped, yellowish orange with a purplish pink to purplish red central stripe. Inner petals 15 – 21mm long, 5 – 6.5mm wide, more or less long-oval-broad-oval, occasionally with frayed tips, orange or light orange with a central, pointed purplish area at the base. 16 – 18 petals in total. Nectary white, tubular, 5 – 8mm long; lower part 0.6 – 0.8mm wide, upper part 1.4 – 2.3mm wide. Nectar groove 1.2mm wide. 55 – 65 stamens. Lowest stamens inserted a little above the nectary, the highest level with the base of the inner petals, or a little below their base. A few filaments inserted here and there between the innermost and the top stamens. Inner stamens 6.5 – 7mm long; stamens longer at the throat of the receptacle, the top stamens 8–10 mm long. All filaments white, more or less cylindrical. Anthers yellowish, 0.9-1,1 mm long, 0.5-0.6 mm wide.

Fruit more or less spherical, 4-6 mm in diameter, with greenish or light grey scales, tearing open when dry; remains of the pericarp visible in the axils of the scales; containing 35-72 seeds. Seed 1.1 – 1.3mm long, 0.8 – 0.9mm wide; more or less pot-shaped (sensu Buxbaum), sometimes a small crest on the ventral side.

The basal region of the hilum, more or less oval, barely slightly concave, contains the scar from the funiculus [stalk] and the micropyle clearly protruding; hilum often covered with whitish-brownish remnants of tissue. The testa is dull brownish-black, with an arillus (in the sense of Buxbaum) descending, adhering to parts of the coat, straight or slightly arched.

Habitat in Santa Victoria, Salta, Argentina, at an altitude of 2500- 2700m.

Additional notes

A few specimens were discovered at the time together with plants of Rebutia hoffmannii Diers & Rausch (1977), which in their severely dried-up state could not be distinguished from those of the species mentioned. It was only after they had filled in culture that they turned out to differ from Rebutia hoffmannii. The observations and investigations carried out in the years that followed strengthened the indication that these plants could not be assigned to any known species. The suspicion of hybridogenicity, possibly with Rebutia hoffmannii, was not confirmed. The offspring used after selfing, which are now available up to the third generation, always consist of specimens that are very similar to each other and to the original mother plants. In order to put the work on a broader material basis, I asked Walter Rausch to look for other sites in the area where the plants in question occur during his Argentina expedition in 1983 and, above all, to collect new specimens.

This material was also compared and examined with that already available and with the many Rebutia strains cultivated here, so that definitive clarity could be gained. The findings showed clearly that the plants discovered together with Rebutia hoffmannii belong to a new species.

Rebutia walteri differs from Rebutia hoffmannii mainly in the following characteristics; the information for Rebutia hoffmannii in brackets: body solitary (proliferating), up to 5 cm (up to 3.5 cm) diameter, dark green (light green); spines max. 25 (about 40), up to 18 mm (up to 12 mm) long, centrals brown (white); receptacle 10-15 (14-21) mm long, yellow-green-light brownish-light violet-pink (purple-pink), receptacle tube with style fusion zone 5.5-9 (9-14.5) mm long; style fusion zone 2.3-5.7 (5.5-11) mm long; Stigma branches cylindrical, blunt (tapering), 0.7-1 mm (0.4-0.7 mm at their base) thick. Fruit green (reddish-reddish violet). Since the differences are varied and significant and no close family relationships can be identified with other known Rebutia genera, the listing of the new species is justified.