Denmoza is a South American genus consisting of one accepted species: D. rhodacantha. Another species has been described as D. erythrocephala, but it is generally not accepted as a “good” species. The species grows in Argentina in the region of Mendoza, of which the genus name is an anagram.
In habitat there are specimens reaching heights of up to 3 meters according to Hunt et.al. in The New Cactus Lexicon. However, the “normal” description of D. rhodacantha calls for a species globular in shape, only elongating towards a slight columnar shape in old age. The plants I have are probably around 25 years old and very much globular at approximately 15-20 cm in diameter and about the same in height.
Described in 1922 by Britton and Rose, the genus Denmoza has later been included both in Cleistocactus and Oreocereus. As can be seen from the flowers on these plants and the specimen of Oreocereus trollii described in a previous post, there are some clear similarities. Some more recent research suggests the genus is more closely related to the genus Acanthocalycium and certain members of Echinopsis s.s. (“sensu stricto”, as in the strict or narrow view of Echinopsis). It is also possible that it arose in the distant past as an intergeneric hybrid between Echinopsis and Oreocereus, as suggested in J. Lodé’s The Taxonomy of the Cactaceae.
The usual descriptions of the species calls for brownish red spines, which certainly doesn’t fit the yellow-spined form I have. The spines on that particular specimen are also slightly stronger than on the brownish-red-spined form. I think they are both very attractive forms and although they take a long time to start flowering (probably at least 15-20 years), they are well worth growing.
I cross-pollinated the two plants as they happened to flower at the same time and intend to sow some of the seeds that resulted from the happy union. I certainly hope the yellow-spined form will show up in some of the seedlings.
It is quite easy to grow and fairly tolerant of adverse conditions. It’s hardy down to at least -5°C and probably a good deal more for short periods. A well-drained porous soil with perhaps 30% organic material will give good healthy specimens.