Regarded by most as a form of Aylostera spegazziniana.

Listed by Mosti & Papini (2011) as a species in its own right, though no information is given other than the Ito reference. Although attributed to Backeberg, no description (of the originally Rebutia waltheriana) appears to exist. Ito provided a new combination and an explanation of the species in “Explanatory Diagram of Austroechinocactinae – Classification of Austroechinocactinae”, Japan Cactus Laboratory, Tokyo, Japan, in 1957, however this, and many of the other species erected, have been refuted. A very scathing review of this book was published by Gordon Rowley in The National Cactus and Succulent Journal 12(4), p.79, December 1957, in which Ito is said to have “worked abundantly to secure perpetuation of his name in the cactus literature: may he now decide to encourage the study of cacti with usable, conservative ideas rather than kill it stone dead with a plethora of fantastic new names.”

A. Wessner listed the plant KR339 (also known as WK339) as A. waltheriana in his 2009 catalogue. This is a somewhat ambiguous plant which has variously been named A. waltheriana, A. spegazziniana, A. minutissima, A. patericalyx; it is regarded as probably the best candidate for the original A. waltheriana.

I have been unable to find a plant under the name Aylostera (or Rebutia) waltheriana (or walteriana), nor the plant KR339 (or WK339). If you have one or know where I can get one, please let me know!