Origin and Habitat: Mammillaria densispinaSN|9237]]SN|20899]] is widespread and relatively common in appropriate habitat on the states of San Luis Potosi, Guanajuato, Jalisco, Aguascalientes, Durango, Queretaro, and Zacatecas, Mexico.
Altitude: It grows at elevations of 1750 to 3000 meters above sea level.
Habitat and Ecology: This species is found in oak forests on volcanic soils often on large rocks, together with Mammillaria pringleiSN|9228]]SN|14527]], Mammillaria giganteaSN|14267]]SN|12777]], Mammillaria monancistracanthaSN|8911]]SN|8911]], Mammillaria uncinataSN|12777]]SN|14267]], Mammillaria jaliscanaSN|14527]]SN|9228]], Mammillaria fuscohamataSN|20899]]SN|9237]], Echinocereus polyacanthusSN|7070]]SN|7070]], Echinocereus polyacanthusSN|7070]]SN|7070]] v. densus, Nolina recurvata, Nolina texana, Nolina bigelowii, Senecio praecox, Agave parryiSN|10450]]SN|247]], Agave salmianaSN|27883]]SN|27883]], Agave filiferaSN|247]]SN|10450]], Arbutus glandulosa, Opuntia robusta, Opuntia streptacantha, Opuntia imbricataSN|28228]]SN|8157]], Opuntia tunicataSN|8157]]SN|28228]], Opuntia scheeri, Opuntia jaliscana, Ferocactus histrixSN|4259]]SN|4300]], Ferocactus latispinusSN|4300]]SN|4259]], Coryphantha erectaSN|3941]]SN|3941]], Myrtillocactus geometrizansSN|8050]]SN|8050]], Dasylirion acrotrichumSN|2998]]SN|2998]], Echinofossulocactus dichroacanthusSN|6255]]SN|6255]], Neolloydia conoideaSN|10089]]SN|10089]], Glandulicactus crassihamatusSN|3435]]SN|3435]], Dodonaea viscosa, Arctostaphylos pungens and Acacia farinosa.

• Mammillaria densispina (J.M.Coult.) Orcutt
• Cactus densispinus J.M.Coult.
• Krainzia densispina (J.M.Coult.) Doweld
• Leptocladia densispina (J.M.Coult.) Buxb.
• Neomammillaria densispina (J.M.Coult.) Britton & Rose

• Mammillaria densispina (J.M.Coult.) Orcutt
• Cactus densispinus J.M.Coult.
• Krainzia densispina (J.M.Coult.) Doweld
• Leptocladia densispina (J.M.Coult.) Buxb.
• Neomammillaria densispina (J.M.Coult.) Britton & Rose
• Mammillaria buxbaumeriana Repp.

Description: Mammillaria densispinaSN|28215]]SN|20899]] is a tiny solitary cactus particularly priced by Mammillaria enthusiast. Its body is densely covered by translucent pale-yellow or amber-brown spines and produces small yellowish flowers in spring. It is vaguely similar in general shape to Mammillaria rhodanthaSN|14510]]SN|14510]], but does not divide itself dichotomously. The taxonomic relationship between this species and Mammillaria microheliaSN|20899]]SN|28215]] needs further investigation.
Habit: Slow-growing, spherical, perennial succulent, usually solitary.
Stem: Globose to short cylindrical, dark green up to 6(-10) cm in diameter and 12 cm tall, entirely hidden by the dense covering of spines.
Tubercles: firm to flabby, conical, short and thick, green, not milky. Axils without bristles,
woolly at first, later naked.
Radial spines: 20-25 or more, glassy white, pale yellow or pale brownish, unequal, rigid, slender, needle-like, slightly spreading, about 1 cm long.
Central spines: 5 or 6, straight, rigid, longer than the radials, bulbous at the base, 10-12(-15) mm long, fuchsine red when new, passing to yellow. Often the upper half or third dark brown.
Flowers: Funnelform, yellow, orangish or purplish without, pale-yellow within, 15-20 long.
Fruits: Elongated, greenish pink or creamy coloured.
Seeds: Obovate, reddish brown, 1 mm in diameter.

Bibliography: Major references and further lectures
1) David Hunt, Nigel Taylor “The New Cactus Lexicon” DH Books, 2006
2) John Pilbeam (1999) “Mammillaria The Cactus File Handbook” Nuffield Press.
3) Edward F. Anderson “The Cactus Family” Timber Press, 2001
4) James Cullen, Sabina G. Knees, H. Suzanne Cubey “The European Garden Flora Flowering Plants: A Manual for the Identification of Plants Cultivated in Europe, Both Out-of-Doors and Under Glass”Cambridge University Press, 11/ago/2011
5) Nathaniel Lord Britton, Joseph Nelson Rose “Cactaceae: Descriptions and Illustrations of Plants of the Cactus Family” vol. 4 The Carnegie Institution of Washington, Washington 1923
6) Hans Hecht “Cacti & Succulents” Sterling Publishing Company Incorporated, 1994
7) Hecht, Hans “BLV-Handbuch der Kakteen.” München ; Wien ; Zürich : BLV-Verl.-Ges. 1982
8) Haustein, Erik. “Der Kosmos-Kakteenführer.” Kosmos / Gesellschaft der Naturfreunde., Stuttgart, 1983
9) Urs Eggli, Leonard E. Newton “Etymological Dictionary of Succulent Plant Names.” Springer, Berlin/Heidelberg 2010
10) John Borg “Cacti: a gardener's handbook for their identification and cultivation” Blandford P., 1970
11) Sánchez , E., Guadalupe Martínez, J. & Bárcenas Luna, R. 2013. Mammillaria densispina. In: IUCN 2013. "IUCN Red List of Threatened Species." Version 2013.2. <www.iucnredlist.org>. Downloaded on 27 November 2013.

Cultivation and Propagation: It is a slow growing species of easy culture, recommended for any collection that needs lots of light with ample airflow. Water regularly in summer, but do not overwater (very wet-sensitively, especially in light of its small root system) Water thoroughly only if soil is dry to the touch, let soil dry in between to prevent root rot, keep dry in winter. Use a very porous mineral-based potting mix, with excellent drainage, as can be achieved by the addition of extra perlite or pumice. Feed with a high potassium fertilizer in summer. Care must be taken with watering as they tends to become swollen and untidy in growth habit if given too much water and shade.
Sun Exposure: High levels of light are needed to flower and for good spine development. Can be sunburned if moved from shade/greenhouse into full sun too quickly. During the spring it may be able to take full sun until the heat arrives at the end of spring. In an area that has hot afternoon sun, it may be able to take full morning sun, but requires afternoon shade or afternoon light shade. If grown correctly, it will reward the grower with generous displays of flowers. It is quite frost resistant if kept dry, hardy as low as -5° C (or less) A resting period in winter and strong light are necessary so that it can flower properly.
Clustering in cultivation after several years and easily flowered. For best results, use a shallow pot, and only use the smallest diameter pot that will accommodate the plant. Sensitive to red spider mite. Overhead watering is helpful in controlling mites.
Propagation: Direct sow after last frost (usually) or division, wait until the offsets that appear at the base of old clustered specimens are 1/3 the size of the parent and then detach and plant.