Genus circumscription and historical names
Plants of the World Online accepts Mammillaria as a separate genus in the family Cactaceae. Its natural range extends from the central United States to Colombia, and includes the Caribbean and Venezuela. The current list of species and their synonyms provides the reference for names in the atlas. [2-WWW]
The rank of some names has also changed among species retained in the genus. Mammillaria vetula includes the historical subspecies gracilis, M. decipiens the historical subspecies albescens, and M. haageana subsp. haageana the name M. san-angelensis. Former names have been retained when identifying study material. This keeps a character of a particular specimen or line linked to its proper scope. [2-WWW] [2-WWW] [2-WWW]
Tubercle and separate growth sites
In the study of material from San Ángel, tubercle primordia appeared beside the main shoot meristem as early as the third day after germination. As they elongated, the meristematic part at the tip produced spines and hairs. A flower-forming zone remained at the tubercle base. This dimorphic areole organisation explains the distance between the flower and the visible cluster of spines. Successive tubercles are elements in the organisation of the growing stem. [López-Ruiz et al. 2026, p. 1330–1334, 1337–1341]
The external surface alone does not determine tubercle anatomy. Tubercles differing in length and firmness were compared in material of M. vetula, M. decipiens and M. longimamma. All had larger vascular bundles, a network of smaller cortical bundles and chlorenchyma, parenchyma containing chloroplasts. No distinct hydrenchyma, specialised colourless water-storage parenchyma, was found in these three types. [Ozerova and Timonin 2020a, pp. 11–14]
Photosynthetic tissue and CAM
Cells of the outer chlorenchyma in the tubercles examined were short and nearly isodiametric, arranged in oblique rows of four or five. The authors described this arrangement as columnar chlorenchyma. Large vacuoles hold the temporary pool of malate in CAM metabolism, and relatively straight spaces between the rows may facilitate CO₂ diffusion into deeper tissue. This is a functional interpretation of the anatomy. Gas exchange in individual plants was not measured in this study. [Ozerova and Timonin 2020a, pp. 12–16]
Microhabitat diversity
A comparison of ten species from the Tehuacán valley showed an association between lower elevations and steeper habitats. In this sample, M. crucigera and M. huitzilopochtli were closely associated with rocks. In M. crucigera, three plants moved onto a cliff had a lower daily maximum temperature in a two-day measurement than three plants on flat ground above it. The difference concerns a particular habitat and measurement times, while preferences across the genus remain varied. [Martorell and Patiño 2006, p. 543–550]
Light, seed origin and seasonal carbon balance
In Mammillaria carnea from the Tehuacán-Cuicatlán valley, germination responses depended on seed family, the mother plant's growing site and the light treatment. In a study of thirty families from three microhabitats, changing from white light to much weaker light enriched in far-red reduced mean germination, with the strength of the response depending on family. Both light properties changed simultaneously. [Matus et al. 2024, p. 2–6, tab. 1–2, ryc. 1–2]
In adult M. heyderi subsp. gaumeri (the study's M. gaumeri) from Yucatán, drought greatly reduced daily CO₂ balance and stopped new areole formation. In the rainy season, almost the entire net balance occurred at night. The greatest growth of adult plants was associated with 60–80% of the local daily radiation total measured above the vegetation. These results concern a specific subspecies, adult specimens and two environments in Yucatán. [Cervera et al. 2007, pp. 620–627. POWO, 11 October 2026] [2-WWW]
In vitro culture, stem organisation and CAM
In Mammillaria vetula material (called M. gracilis in the studies), normal in vitro shoots, hyperhydric shoots, callus and tumour tissue induced by Agrobacterium differed in photosystem II efficiency and daily changes in acidity. Normal shoots retained a rhythm of nocturnal acid accumulation, weaker than in potted plants. No significant nocturnal increase in acidity was found in callus, hyperhydric shoots or tumour tissue, despite detected phosphoenolpyruvate carboxylase activity. Spine length and surface also changed in culture. These relationships describe the gracilis material studied, which was separate from the cultivar ‘Snowcap’. [Balen et al. 2012, Balen et al., pp. 1884–1891. Peharec et al., pp. 79–85. POWO, 11 October 2026] [Peharec et al. 2010, Balen et al., pp. 1884–1891. Peharec et al., pp. 79–85. POWO, 11 October 2026] [2-WWW]