Limits of the genus

There has been considerable debate about the extent of the genus. In the middle of the twentieth century there was a tendency to separate groups of plants within Rebutia as new genera, e.g. Mediolobivia, whereas towards the end of the century the reverse tendency predominated, with genera previously regarded as separate, such as Weingartia, being subsumed within Rebutia. At the beginning of the twenty-first century there was a broad consensus, as reflected in Kew's list of Vascular Plant Families and Genera, that the following genera should be regarded as synonyms of Rebutia:^[5]

Kew's Plants of the World Online accepts Aylostera Speg.^[6] and Reicheocactus Backeb. 1942.^[7]

(The generic names Bridgesia, Spegazzinia, Echinorebutia, Eurebutia, Mediorebutia, Neogymnantha and Setirebutia are invalid, the first two because they are homonyms of Bridgesia Bert. ex Cambess. and Spegazzinia Backeb. respectively,^[8] the remainder for lack of any valid publication. Some of these are nevertheless valid names for subdivisions of the genus.)

The history of the taxonomic treatment of the genera Rebutia, Aylostera, Weingartia, Sulcorebutia and Cintia is summarized below.^[9]

The variation in the treatment of the genus is illustrated by the difference between Mosti et al., who in 2011 treated Aylostera and Weingartia (including Cintia and Sulcorebutia) as distinct from Rebutia,^[9] and Plants of the World Online, which as of October 2023 continued to separate Aylostera, but merged Cintia, Sulcorebutia and Weingartia into Rebutia.^[1]

Species

The number of species is similarly debatable, because of disagreement both over what constitutes the genus and what constitutes a species. A very large number of plants that have circulated as species of Rebutia are now generally regarded as varieties, forms or synonyms of others.^[10] E. F. Anderson recognised forty-one species in 2001.^[11] The following species are accepted by Plants of the World Online as of October 2023:^[1]

Image	Scientific name	Distribution
	Rebutia arenacea Cárdenas	Bolivia
	Rebutia borealis Diers & Krahn	Bolivia
	Rebutia breviflora (Backeb.) D.R.Hunt	Bolivia
	Rebutia canigueralii Cárdenas	Bolivia.
	Rebutia cardenasiana (R.Vásquez) G.Navarro	Bolivia
	Rebutia cintia Hjertson	Bolivia.
	Rebutia cylindrica (Donald & A.B.Lau) Donald	Central Bolivia
	Rebutia fabrisii Rausch	Argentina
	Rebutia fidaiana (Backeb.) D.R.Hunt	Bolivia
	Rebutia glomeriseta Cárdenas	Bolivia
	Rebutia krugerae (Cárdenas) Backeb.	Bolivia
	Rebutia mentosa (F.Ritter) Donald	Bolivia.
	Rebutia minuscula K.Schum.	Argentina
	Rebutia nataliarum V.Gapon	Bolivia.
	Rebutia neocumingii (Backeb.) D.R.Hunt	Peru to Bolivia.
	Rebutia neumanniana (Backeb.) D.R.Hunt	Bolivia to Argentina
	Rebutia oligacantha (F.H.Brandt) Donald ex D.R.Hunt	Bolivia
	Rebutia padcayensis Rausch	Bolivia to Argentina (Salta)
	Rebutia steinbachii Werderm.	Bolvia
	Rebutia tiraquensis Cárdenas	Bolivia

Phylogeny

Recent research has indicated that the genus Rebutia as currently defined is polyphyletic. Sulcorebutia and Weingartia were kept as separate genera in the study; a summary cladogram for those species studied is shown below.^[12]

Species formerly classified as Weingartia, Sulcorebutia and Cintia show a close relationship to each other and to species of Rebutia with naked pericarpels (Rebutia II), including the type species R. minuscula. The larger group of species of Rebutia studied, those with hairy or bristly pericarpels, form a separate, more distantly related clade (Rebutia I). It is suggested that these be excluded from the genus.^[12]