One species and two former combinations
In the Plants of the World Online treatment checked on 10 October 2026, Obregonia is a monotypic genus. Its only accepted species remains O. denegrii Frič. The genus and species name were published in 1925. The database places it in Cactaceae and gives the genus's natural range in northeastern Mexico. [2-WWW]
The former combinations Ariocarpus denegrii (Frič) W.T.Marshall and Strombocactus denegrii (Frič) G.D.Rowley are synonyms of Obregonia denegrii. They refer to the same species. Resemblance of its broad tubercles to some Ariocarpus is an appearance feature, while the accepted current classification retains a separate genus. [2-WWW]
Rosette structure and limestone habitat
The solitary, low stem consists of overlapping triangular tubercles. Each narrows towards a small areole, woolly when young and bearing few soft spines. Pale flowers arise near the woolly tip from young areoles. The IUCN description presents a compact body 8–12 cm in diameter. Fleshy tissues, including spindle-shaped roots, make up most of the plant. [Lucas and Synge 1978, p. 108 and p. 1768] [Martínez-Berdeja and Valverde 2008, p. 108 and p. 1768]
Older field accounts and ecological experiments focus on the Jaumave Valley in Tamaulipas. The IUCN account describes dry, rocky limestone hills at around 800 m above sea level, among shrubs and other cacti. The current species record in POWO lists Tamaulipas and Nuevo León. Data on specific sites and the range accepted in the database differ in detail. [Lucas and Synge 1978, IUCN p. 107] [Martínez-Berdeja and Valverde 2008, IUCN p. 107] [2-WWW]
Growth and reproductive biology
Six-month-old seedlings responded to water availability in a greenhouse by changing growth rate and partitioning of dry biomass between root and stem. No significant change in these parameters was found at the two light levels applied. The observation concerns seedlings within a specified range of conditions and helps explain one mechanism through which nurse plants act. [Martínez-Berdeja and Valverde 2008]
Seeds allow material originating from many parent plants to enter propagation. Activating areoles in culture permits numerous shoots to be obtained from seedling fragments. Formation of somatic embryos from vegetative tissues has also been described in the species. The methods differ in regeneration pathway, medium composition and acclimatisation requirements. Details of structure, sowing and cultivation are in the account of O. denegrii. [Cardarelli et al. 2010] [Malda et al. 1999b]
