Name and genus circumscription
Franz Buxbaum published the genus Mammilloydia in 1951. Plants of the World Online accepts M. candida within it. In this treatment, the names Mammilloydia ortizrubioana, Mammillaria estanzuelensis and the historical subspecies menchacaensis and ortizrubioana are synonyms of one species. Descriptions of varieties on archival labels therefore refer to variation within the material covered by this account. [2-WWW] [2-WWW]
In the 2026 paper by Solórzano and colleagues, the species appears under the name Mammillaria candida. The authors use a broader circumscription of Mammillaria, and the results concern the same plant that the atlas presents as Mammilloydia candida. This treatment allows the publication to be found by its original title and connects the account's current name with the former name of the material studied. [Solórzano et al. 2026] [2-WWW]
Structure of stems, flowers and seeds
The stems are globose to shortly cylindrical, solitary or branched from the base. The surface consists of spirally arranged tubercles, with spines grouped in areoles at their tips. Bristles grow between the tubercles. Numerous white radial spines overlap to form a pale covering. The central spines may have pink or brown tips. The regional Flora del Bajío description reports watery sap and blue-green tubercles. [Arias and Aquino 2019, pp. 124–125, regional description]
The flowers have a well-developed perianth, and elongated, pale fruits later appear between the tubercles. In the regional description, the seeds are black and about 1.2 mm long. Their surface has elongated seed-coat cells and recessed boundaries between cells. Seed morphology is one of the elements used in discussing the distinctness of Mammilloydia. [Arias and Aquino 2019, p. 124–125]
Pozycja ewolucyjna
The analysis by Chincoya and colleagues included 52 plastid loci from 142 chloroplast genomes, representing 103 taxa in the mammilloid clade. Material identified as Mammillaria candida formed, with M. albiflora, an early lineage sister to the other sampled lineages in the clade. The result shows that similar tuberculate stems coexist with substantial diversity in evolutionary history. [Chincoya et al. 2023, pp. 3–8, 12–14]
Conclusions about genus boundaries depend on the scope of sampling and the type of genetic data. Plastid loci describe the history of one linked organelle genome. The authors of the 2023 study identify a need to resolve classification further, especially since their sample lacked Mammillaria mammillaris, the type species of Mammillaria. The current account retains the accepted POWO treatment and gives the alternative name when discussing the publication. [Chincoya et al. 2023, Chincoya et al., pp. 12–14] [2-WWW]
Range and population structure
Field verification in 2023–2025 confirmed sites in Coahuila, Nuevo León, San Luis Potosí and Tamaulipas. Plants mainly occupied upland hills and foothills of the Sierra Madre Oriental. They occurred among shrubs and rosette-forming plants, and in soil-filled rock crevices. Locally, they formed small, separated groups, although the environmental model indicated a more extensive belt of potentially suitable habitats. [Solórzano et al. 2026, p. 5–10]
A study of five nuclear microsatellite markers detected high diversity and regional structure. Preserving sites in different parts of the range allows distinct components of this variation to be maintained. Numerical details, the proportion of protected areas and limitations of inference are presented in the species account and the article on habitats and genetics. [Solórzano et al. 2026, p. 10–16]