Rebutia (Aylostera) einsteinii was first described by A. V. Frič, in Möllers Deutsche Gärtner Zeitung, 63: 23, p. 267, in 1931. The account is a chatty article, in German, of Frič’s exploits in finding the plants and growing them on as grafts. The plant is first named there (as Rebutia einsteinii) but there is little actual description other than to say the plant is small (Frič put it in his pocket), grows at very high altitude (5700m) and has large yellow flowers.

The species was further described in other publications in later years. Here are the main features:

Bodies tap-rooted, brownish green, sometimes with a purplish cast, 2cm – 4cm in diameter, about the same in length, sometimes longer, branching with age.

Areoles quite elongated and a wide range of colours from white through brown to black. No central spines except in older plants, but usually about 10 radial spines (can be more), quite fine, usually spreading outwards along the body; all the same length but vary from plant to plant, some being short-spined.

Flowers yellow to orange-yellow*, 25mm to 40mm in diameter and the same length, with yellow, greenish-yellow or whitish stamens, style and stigmas. Flower buds are very hairy. A key difference between this species (group) and others is that the style is not fused to the flower tube, and the tube is very thick in comparison, at up to 4.5mm at the narrowest point.

*Note that descriptions in various publications are difficult to reconcile, mainly because different authors regard different plants as being not distinct from A. einsteinii (A. gongianii, for example). Pink, red and salmon-coloured examples of A. einsteinii have been described. As yet none of these are in the collection.