Parental names in the source and today
González-Zamora, Aquino and Sánchez described Stenocactus × irregularis as a hybrid of S. coptonogonus and S. pentacanthus. POWO currently accepts the name S. obvallatus, in which it includes S. pentacanthus. In today's nomenclature, the proposed parental pair is therefore written as S. coptonogonus × S. obvallatus. The hybrid name is accepted in POWO.[González-Zamora et al. 2023, pp. 89–90, 95–101; POWO, checked on 11 October 2026][2-WWW]
The paper was published electronically on 13 December 2022, while volume 75 of Brittonia is dated 2023. The type material comes from near San Diego de la Unión in Guanajuato. It was collected on 7 July 2020, and the principal specimen is held in the IBUG herbarium. The hybrid study site lay at 2285 m elevation.[González-Zamora et al. 2023, pp. 89, 91, 97–98]
Comparison of 132 adult plants
The analysis included 53 individuals of S. coptonogonus, 56 identified in the study as S. pentacanthus and 23 hybrids. Three populations were used for each parent. Hybrids were examined at a site near San Diego. The authors measured stems and ribs and assessed spines in ten areoles on each plant. Of seven characters, one was removed before analysis because it was strongly associated with another character.[González-Zamora et al. 2023, pp. 90–94, Tables 1–2]
| Group | Number of plants | Mean ± SD | Range |
|---|---|---|---|
| S. coptonogonus | 53 | 13,0 ± 0,39 | 12–14 |
| S. obvallatus (S. pentacanthus in the study) | 56 | 37,0 ± 4,9 | 30–53 |
| S. × irregularis | 23 | 19,0 ± 3,6 | 15–28 |
Discriminant analysis of six characters separated three morphological groups. Its first axis explained 99,9% of discriminant variation, with rib number contributing most. This percentage describes separation of the groups in the space of the measured characters. It does not determine the proportions of parental genomes in the hybrid.[González-Zamora et al. 2023, pp. 92–95, Tables 2–4, Figure 2]
Complete ribs and ribs that end on the stem
A complete hybrid rib runs along the stem, while an incomplete rib ends partway along it. The authors usually recorded 3–6 incomplete ribs, with a wider range of 1 to 18. Some ended before forming an areole. The combination of 15–28 complete ribs and incomplete ribs gives the stem an irregular arrangement of ridges.[González-Zamora et al. 2023, pp. 95–98, Figures 3–4]
The plant has an extensive underground stem section and a turnip-shaped root thickened in its upper part. The above-ground stem may be partly embedded in the substrate. In the taxonomic description, it is 5–11 cm tall and usually 7,5–10 cm in diameter. At the deeper-soil site, hybrids co-occurred with S. coptonogonus. They were also found in rockier places with the other parent. These are distribution observations, without an experiment on conditions for growth of the underground stem.[González-Zamora et al. 2023, pp. 97–101]
The flower, fruit and seeds
The hybrid's flowers measured 21–28 mm in length. Inner tepals were white with a longitudinal purple stripe, and the innermost tepals were distinctly shorter. Dry fruits opened at the side or at their connection to the perianth remains. Seeds were about 0,9–1,1 mm long. Flowering occurred mainly in January and February, sometimes March, and fruits were observed in April and May.[González-Zamora et al. 2023, pp. 98–100, Figures 5–6]
The authors sowed 85 seeds from three hybrid plants. Of this sample, 78% germinated. The result documents the ability of some collected seeds to germinate. The article did not give the conditions or duration of this trial, so it does not allow a complete sowing method to be reproduced or subsequent seedling survival to be assessed.[González-Zamora et al. 2023, pp. 98, 101]
Basis of the origin hypothesis
Intermediate and distinctive morphological characters, proximity to the proposed parents and overlap of their flowering in February supported a hybrid origin. No DNA analysis or controlled crossing of the parents was performed during the study. Origin was therefore explained by agreement between morphological and field data.[González-Zamora et al. 2023, pp. 99–101]
The main observations concerned the vicinity of San Diego de la Unión. Material cited in the publication also includes a 2022 specimen from Santa María del Río in San Luis Potosí. This additional record distinguishes the scope of the morphometric measurements from the broader set of documented occurrence sites.[González-Zamora et al. 2023, pp. 98–99]
A new hybrid species of Stenocactus (Cactaceae) from the Bajío region, Mexico
González-Zamora P., Aquino D., Sánchez D., A new hybrid species of Stenocactus (Cactaceae) from the Bajío region, Mexico, Brittonia, 2023, 75(1):89-102, doi: 10.1007/s12228-022-09733-9
A description of Stenocactus × irregularis and a morphometric analysis of 132 adult plants of the hybrid and its proposed parents. The paper presents rib, underground stem, flower and seed traits, and a germination trial.
Plants of the World Online — Royal Botanic Gardens, Kew
Accepted names, synonyms and distribution. A citation beside a taxon leads to its record.
Accessed 2026-10-08.