Mammilloydia candida

Identity and former names

The accepted name is Mammilloydia candida (Scheidw.) Buxb. The basionym Mammillaria candida Scheidw. appeared in 1838, and the combination in Mammilloydia in 1951. Both names refer to the same nomenclatural type. POWO also includes here plants described as Mammillaria ortizrubioana, M. estanzuelensis and the subspecies menchacaensis and ortizrubioana. [2-WWW]

In 2026, Solórzano and colleagues use the name Mammillaria candida. When checking historical locations, they identified other species at some of them. In Xichú they found M. muehlenpfordtii, and in Atarjea M. geminispina. At other checked sites, incorrect records concerned species including M. lasiacantha and M. formosa. These are results from verifying specific locations. Establishing the full limits of variation in M. candida still requires a formal taxonomic revision. [Solórzano et al. 2026, pp. 5–6, 13–15]

Stem, tubercles and spines

Flora del Bajío describes the stems as solitary or offsetting, globose to shortly cylindrical, usually up to 11 cm high, exceptionally up to 30 cm, and 6–14 cm in diameter. The tubercles are 0.8–1.3 cm long and 0.4–0.6 cm wide at the base, arranged in 8/13 or 13/21 spirals. Areoles are round, and the axils between tubercles contain bristles. These dimensions come from the 2019 regional account, some of whose distribution data were later challenged during field studies. [Arias and Aquino 2019, Flora del Bajío, pp. 124–125. Solórzano et al., pp. 5–6] [Solórzano et al. 2026, Flora del Bajío, pp. 124–125. Solórzano et al., pp. 5–6]

The same description gives usually 30–60 radial spines, sometimes 25, up to 1.5 cm long. They are thin, needle-like and white, with reddish tips in some material. There are usually 6–12 central spines, sometimes four. They are straight and somewhat stiffer, usually up to 1 cm long, exceptionally up to 1.5 cm, with pink or brown tips. The dense, overlapping spines are the plant's most readily visible feature. [Arias and Aquino 2019, p. 124, regional description]

Flowers, fruits and seeds

The regional description gives flowers 2.5–3 cm long and about 3.5 cm in diameter. The inner tepals are yellowish to white, with a brown central stripe. The style is pink, and the stigma has four to seven lobes. Variation in flower appearance should be considered together with material origin. These data refer to the Flora del Bajío diagnosis, and the colour stated in that diagnosis remains separate from the appearance of specimens photographed in other parts of the range. [Arias and Aquino 2019, p. 124–125]

The fruits in the description are whitish-pink, club-shaped and 0.7–1.4 cm long. They emerge between the tubercles, shedding the dried perianth remains. They contain black seeds about 1.2 mm long. The seed-coat surface has elongated cells, flat to slightly raised outer walls and groove-like boundaries between cells. Flowering in March and April was reported regionally. [Arias and Aquino 2019, p. 124–125; fenologia regionalna]

Confirmed sites and microhabitats

Four expeditions were carried out in 2023–2025, checking 62 sites in nine Mexican states. After observations were combined with cleaned GBIF records, 254 occurrence records remained, comprising 136 from San Luis Potosí, 53 from Nuevo León, 44 from Tamaulipas and 21 from Coahuila. This is a count of location records, dependent on collection and documentation history. The authors assessed individual population sizes separately during fieldwork. [Solórzano et al. 2026, p. 2–6; tabela 1]

Confirmed sites lay at approximately 1140–2160 m above sea level. Plants occurred beneath low shrubs, between Yucca and Opuntia, and among rosettes of Agave, Hechtia and Nolina. Open, unsheltered places were occupied less often. On cliffs, the cacti rooted in crevices that accumulated soil and moisture. At some of the most populous sites, the substrate was dark, clayey and stony, while at others it was shallow or sandy. [Solórzano et al. 2026, pp. 5–6, 13–15, elevations rounded]

In Coahuila, some of the groups observed contained only three to nine plants. Larger groups were found elsewhere in the range. Plants were concentrated on small parts of hills, separated by areas without confirmed occurrence. The scattering of these patches matters when assessing habitat continuity and the possibility of preserving regional variation. [Solórzano et al. 2026, pp. 5–6, 13–15]

Genetic diversity

Sequencing of the plastid ycf1–ycf2 fragment included 20 plants from four sites, five from each. Two haplotypes were detected, one at the two sampled San Luis Potosí sites, the other in Nuevo León and Tamaulipas. This means there were two variants of the chloroplast fragment studied in this sample. [Solórzano et al. 2026, pp. 3–4, 10–11]

Analysis of five nuclear microsatellite markers included 95 individuals from eight locations. A total of 138 alleles were detected, along with structure that allowed groups from San Luis Potosí, Nuevo León and Tamaulipas to be separated. The largest share of variation, 88.8% in the AMOVA partition used, occurred within populations. The Coahuila sample contained two plants and needs to be expanded to assess this part of the range in comparable detail. [Solórzano et al. 2026, pp. 10–12, Tables 3–4 and AMOVA]

The authors link the observed heterozygote deficit to possible mating between related plants in small groups. Limited pollen transport is among the causes considered. The study examined genetic markers. Identifying effective pollinators and directly measuring seed movement remain separate research questions. [Solórzano et al. 2026, pp. 12, 15–16]

Habitats and conservation

A model combining climate and soil properties indicated 37 519.32 km² of potentially suitable area. Protected areas covered 1.45% of this modelled area. None of the 254 verified location records lay within the protected boundaries considered. The model's area describes the environmental similarity of map cells to conditions at known sites. Actual occurrence was confirmed in the field. [Solórzano et al. 2026, pp. 7–10, Table 2 and Fig. 5]

During visits, habitat changes in Coahuila were documented, including land occupation by a farm, a scrapyard, industrial development and expansion of the Ramos Arizpe–Saltillo urban area. The authors identify preservation of habitats and distinct regional components of variation as the basis for conservation action. Long-term monitoring of survival, recruitment and abundance would allow the rate of population change to be determined. [Solórzano et al. 2026, pp. 13–16]

Related articles

Materials from the author's archive

The species also appears in Konrad Szychowski's private material archive. [Kaktologia 2009b, file p. 13] [Neciu b.d., file p. 1]