In northwestern Argentina, the Calchaquíes Valleys are an ecosystem formed by a set of valleys, rivers, mountains and coloured quebradas, which constitute a strongly xerophytic habitat. The Valleys run along the Andean foothills to the west of the provinces of Catamarca, Tucumán and Salta. They start at the threshold of Belén (Catamarca), and lead up to the Quebrada del Toro (Salta), approximately 400 km as the crow flies. For about 325 km, the various populations which make up the taxon known as Echinopsis thionantha (Spegazzini) Werdermann can be encountered in a spatial continuum. Starting from La Cienaga de Abajo, 19 km north of Belén (Kiesling reports disjointed populations of the taxon in Famatina, La Rioja (2005, 88), there are globular populations with grey blue epidermis and black spines when it’s young, known as Echinopsis glaucina H. Friedrich & G. D. Rowley or Echinopsis thionantha ssp. glauca (F. Ritter) Lowry. Then we arrived at La Poma, 51 km north of Cachi (Salta) for the most northwesterly populations. Right after La Cienaga, in the direction of Hualfín, the taxon begins to elongate, <46 cm (A & M 451, photos 57-60), arriving at <65 cm (A & M 151, photo 19), or reaching a size of <39 x 25 (h x ø), with 25 ribs (photos 20-23), in the centre of the distribution area (Cafayate, Angastaco, Quebrada de Las Conchas). The body becomes a grey-green, and the areoles have a greater number of spines, although shorter, compared to populations at La Cienaga. E. thionantha is a perfect example of a dominant species. i.e. more opportunistic and therefore better at adapting to different habitats, resulting in a greater numerical progression of individuals and populations, and higher variability. This case gives us the opportunity to highlight how certain differences brought to distinguish groups of related taxa, once the verifications in habitat have been made, often have little consistency. As already mentioned, in the southernmost distribution area, the populations of the form glaucina or glauca, which we will call glaucina populations, are distinguished from E. thionantha as being smaller, with less ribs (8-14 vs. 9-15), less spines, but longer > 1 cm (Hunt et al. 2006, text: 102-103). We have also already mentioned how these populations, whose distinctive characters (in addition to a generally globular form) are actually the grey-blue epidermis and the black young spines (A & M 442, photos 31-47) begin to elongate between La Cienaga de Abajo and Hualfín. In this area we are witnessing the intergradation of the glaucina populations into the thionantha populations (A & M 451, photos 48-60). Now, even though we do not recognize the need for infra or intra specific ranks, we would like to point out that in order for two subspecies of the same species to exist, they should benefit from a minimum of territorial autonomy. If there is a spatial continuum between populations, which makes up a natural species, and the "distinct" forms blend together, it is clear that we are talking about the same biological species, and that it is useless to demand different species or subspecies to indicate the variations in question. In our opinion, we are not even dealing with populations crossing with each other, giving rise to intermediate forms, but the same population that has already been transformed in space and time. In truth, the species has also continued to change in other parts of the distribution area, but these trasformations did not lead to different forms being demanded. We also have the case of scattered individuals (not populations), which in some zones of the distribution area of the species were assumed to belong to the subspecies rank, under the name Echinopsis thionantha ssp. ferrarii (Rausch) Lowry (Hunt et al. 2006, text: 102-103), or to the species rank, in another genus such as Acathocalycium ferrarii Rausch (Anderson 2001, 105; 2005; 2011). In April 2011, we dedicated ourselves to the surveys in the area of Amaicha del Valle (Tucuman, AR), the range of the subspecies ferrarii. We were southeast of Amaicha in El Remate, in the eastern areas of El Tio and of the Observatorio. We went northwest to the Rio Calchaquies, then past Quilmes crossing the valley, and a further 10 km until we arrived at the Rincón de Quilmes. The taxon is indicated by the following characters: globose habit <12 cm, green, about 18 ribs, awl like spines, central 1-4 <1.5 cm, radial 7-9, <2 cm, flowers from yellow to orange red, to carmine <5.5 x 5 cm (Anderson 2001, 105, 2005, 2011). Among these, the only characters that might distinguish the taxon from E. thionantha are the colour of the stem, green to grey-green, and according to Kiesling and Ferrari (2005, 90) the fact that the stems are depressed or globose, never cylindrical like in E. thionantha, and not so grey. Regarding flowers, Kiesling and Ferrari tell us that on the western side of the valley (Rincón de Quilmes), where the type was detected, they are red, while on the other side (east of Amaicha) populations have flowers ranging from yellow to red, with all the intermediate tones in between. Populations of E. thionantha are living all over the examined area, which (of course) in addition to the globular shape, can lengthen in growing. Within these populations, one can identify some individuals (usually isolated), which show the characters that would be distinctive of ssp. ferrarii, or A. ferrarii (A & M 460, photos 67-70, 74-75, 81-84, 86, 97-102, A & M 471, photos 121-124), and living beside the more elongated conspecific examples (A & M 460, photo 86, A & M 471, photos 123, 125). To emphasize the variability of the populations, we would also cite the example of the survey carried out in the south of Amaicha, where some specimens have the characters of the glaucina populations (A & M 469, photos 115-120). It should be noted that also in this case the form can be either glubular or elongated. As highlighted, E. glaucina / E. thionantha ssp. glauca and A. ferrarii / E. thionantha ssp. ferrarii are phases in the transformation process of E. thionantha, the first at the intra-populational level, the second at the infra-populational level. In both cases, it seems appropriate to consider the taxa concerned as synonyms of the dominant E. thionantha. (Quoted from: Anceschi & Magli 2013b, 52-55)