Rebutia (Aylostera) fusca was first described by Friedrich Ritter in Kakteen und andere Sukkulenten 28(4): p. 78, the journal of the Deutsche Kakteen-Gesellschaft, in 1977.

The description is reproduced here in the original Latin as published, together with my own translation in English. The description is rather brief but is expanded upon, in German, in Ritter’s book “Kakteen in Südamerika”, vol. 2, pp. 614-5, with a black-and-white photograph on p. 792, self-published in 1980.

Rebutia fusca Ritter spec. nov.

Plerumque solitaria, viridis, 2 – 4 cm crassa; costae 13 – 17, dissolutae, 1,5 – 3 mm altae; areolae 1 – 1,5 mm longae, lana brunnea obtectae; spinae marginales 8 – 14, pectinatae, 1,5 – 3 mm longae, adpressae, rufae, interdum flavae, basi rufa; saepius 1 – 2 centrales, crassiores, rufae vel atrae, 2 – 3 mm longae.
Flores 28 – 34 mm longi; ovarium lana alba et saetis pallidis instructum; stylus 5 – 8 mm cum tubo coalitus; sulcus nectarifer 0,5 – 2 mm longus; tubus floralis 3 – 5 mm longus, interne albidus, externe lana exigua instructus; filamente alba sine lacuna insertiorum; stylus et 4 – 5 stigmata pallidissime viridia ; petala miniata vel coccinea, spathulata vel linearia, 12 – 20 mm longa, 5 – 8 mm lata, obtusa; semina 1,2 mm longa, vix tuberculata; habitat Tarija ad occidentem versus, Bolivia.
Sammelnummer FR 940.

English translation

Rebutia fusca Ritter spec. nov.

Generally solitary, green, 2 – 4cm thick; 13 – 17 ribs, separated into tubercles 1.5 – 3mm high; areoles 1 – 1.5mm long, covered in brown wool; 8 – 14 marginal spines, comb-like, 1.5 – 3mm long, flattened against body, red, sometimes yellow with red base; often 1 – 2 central spines, stronger, red or black, 2 – 3mm long.

Flowers 28 – 34mm long; ovary with white wool and pale bristles; style fused with the tube for 5 – 8mm; nectary groove 0.5 – 2mm long; flower tube 3 – 5mm long, white inside, the outside with a little wool; filaments white inserted without hole; style and 4 – 5 stigmas pale green; petals red or scarlet, spatulate or linear, 12 – 20mm long and 5 – 8mm wide, blunt-tipped; seeds 1.2mm long, barely bumpy; habitat Tarija and westwards, Bolivia.

Collection number FR 940.