Origin and Habitat: Mammillaria pottsiiSN|9355]]SN|9355]] has a very wide range, is abundant, and occurs in the states of Chihuahua, Coahuila, Durango, San Luis Potosí, Zacatecas in Mexico, and in Texas in the USA (South Presidio Co., North to near Shafter; SW Brewster Co., N to near Nine-Point Mesa).
Altitude range: The species is reported at elevations of 300 to 2,100 metres above sea level.
Habitat and Ecology: This cactus grows in limestone hills, slopes, mesas, and flats habitats with little if any humus. It occurs in pure limestone crevices in xerophyllous scrub together with Agave lechuguillaSN|23013]]SN|23013]]. It also grows in gravelly areas of hills and washes in desert. There are no known major threats to this species.

• Mammillaria pottsii Scheer ex Salm-Dyck
• Cactus pottsii (Scheer ex Salm-Dyck) Kuntze
• Chilita pottsii (Scheer ex Salm-Dyck) Orcutt
• Coryphantha pottsii (Scheer ex Salm-Dyck) A.Berger
• Krainzia pottsii (Scheer ex Salm-Dyck) Doweld
• Neomammillaria pottsii (Scheer ex Salm-Dyck) Britton & Rose

• Mammillaria pottsii Scheer ex Salm-Dyck
• Cactus pottsii (Scheer ex Salm-Dyck) Kuntze
• Chilita pottsii (Scheer ex Salm-Dyck) Orcutt
• Coryphantha pottsii (Scheer ex Salm-Dyck) A.Berger
• Krainzia pottsii (Scheer ex Salm-Dyck) Doweld
• Neomammillaria pottsii (Scheer ex Salm-Dyck) Britton & Rose
• Mammillaria leona Poselg.
• Leptocladia leona (Poselg.) Buxb.

Description: Plants more or less cespitose branching basally and along the stems, although single-stemmed, presumably young plants are not uncommon. This species is widely grown in collections but the flowers are inconspicuous. M. pottsii is similar to some plants of Coryphantha tuberculosaSN|9938]]SN|10190]] and Coryphantha sneedii var. albicolumnariaSN|10190]]SN|9938]], both of which occur in the same area, but these species are readily distinguished by stem, spine, flower, and fruit characters.
Derivation of specific name: Presumably, the specific epithet honors E H. Potts (1824-88), a mining engineer in the Sierra Madre, Mexico. Reportedly, Potts was a source of cactus plants for the Kew Royal Botanic Gardens in London and ultimately for the foremost German cac-tologist, Salm-Dyck. Instead, the epithet may be for John Potts (see Opuntia pottsiiSN|19900]]SN|19900]]).
Stems: Cylindrical or clavate, blue green, (6-)12-15(-20) cm long or more, (1.5-)2.5-3(-4) cm in diameter, and completely obscured by whitish radial spines. The stems of M. pottsii do not produce latex.
Tubercles: Almost hidden by the spines, closely aggregated, conical to ovate in shape, 3-5 mm long, blue-green, and tough in texture, without latex. Axils between the tubercles exhibit abundant and persistent white wool. In the flowering zone the longest axillary wool is longer than the tubercles.
Radial spines: About (17-)30-45, appressed, slender, interlacing and straight, 3-4.5(-6) mm long,white or pale tan, weak.
Central spines: 6 to 12 (usually 7), much stouter and longer, contrast sharply with the slender, numerous, whitish radial spines, They are rigid, swollen basally, spreading, more or less ascending, greyish, reddish, brown to bluish black or nearly white, with darker tips, 4-12 mm long, upper one stout, characteristically is curved upward and blue-gray on the distal half. In this feature young single-stemmed plants of M. pottsii may resemble Echinomastus mariposensisSN|26084]]SN|26084]] that occurrs in the same area. Juvenile specimens typically have fewer central and radial spines. In lower (older) areoles of juveniles there are perhaps 2-3 central spines, and the number of centrals increases to about five in areoles at midstem. Even in juveniles the centrals are packed together in an oval configuration, bulbous-based and diffusely spreading.
Flowers; Born in a circle about 2 cm below top of plant, campanulate but not opening widely, brownish red, deep red, or rusty-red, or reddish-purple, about 9-15 mm long and 6-13 mm in diameter; inner perianth-segments light purple, somewhat reflexed near the tips, acute usually with a darker midregion and paler margins. Stamens pale cream-colored to pale yellow, much shorter than the style, purplish above; stigma-lobes 4-5 narrow reddish-purple to orange-yellow.
Phenology (in habitat): This species blooms in late February to March, rarely later. The small flowers of M. pottsii open about noon or before for at least three days, often 5-6 days, and close at night.
Fruits: Red, clavate about 15 mm long. Fruit development and ripening under natural conditions appear to require one to several months.
Seeds: Black, blackish brown, or dark reddish-brown the surface deeply, nearly oval, and ca. 1 mm long.
Chromosome nunmber: 2n = 22.

Bibliography: Plants more or less cespitose branching basally and along the stems, although single-stemmed, presumably young plants are not uncommon. This species is widely grown in collections but the flowers are inconspicuous. M. pottsii is similar to some plants of Escobaria tuberculosa and Escobaria albicolumnaria, both of which occur in the same area, but these species are readily distinguished by stem, spine, flower, and fruit characters.
Derivation of specific name: Presumably, the specific epithet honors E H. Potts (1824-88), a mining engineer in the Sierra Madre, Mexico. Reportedly, Potts was a source of cactus plants for the Kew Royal Botanic Gardens in London and ultimately for the foremost German cac-tologist, Salm-Dyck. Instead, the epithet may be for John Potts (see Opuntia pottsii).
Stems: Cylindrical or clavate, blue green, (6-)12-15(-20) cm long or more, (1.5-)2.5-3(-4) cm in diameter, and completely obscured by whitish radial spines. The stems of M. pottsii do not produce latex.
Tubercles: Almost hidden by the spines, closely aggregated, conical to ovate in shape, 3-5 mm long, blue-green, and tough in texture, without latex. Axils between the tubercles exhibit abundant and persistent white wool. In the flowering zone the longest axillary wool is longer than the tubercles.
Radial spines: About (17-)30-45, appressed, slender, interlacing and straight, 3-4.5(-6) mm long,white or pale tan, weak.
Central spines: 6 to 12 (usually 7), much stouter and longer, contrast sharply with the slender, numerous, whitish radial spines, They are rigid, swollen basally, spreading, more or less ascending, greyish, reddish, brown to bluish black or nearly white, with darker tips, 4-12 mm long, upper one stout, characteristically is curved upward and blue-gray on the distal half. In this feature young single-stemmed plants of M. pottsii may resemble Echinomastus mariposensis that occurrs in the same area. Juvenile specimens typically have fewer central and radial spines. In lower (older) areoles of juveniles there are perhaps 2-3 central spines, and the number of centrals increases to about five in areoles at midstem. Even in juveniles the centrals are packed together in an oval configuration, bulbous-based and diffusely spreading.
Flowers; Born in a circle about 2 cm below top of plant, campanulate but not opening widely, brownish red, deep red, or rusty-red, or reddish-purple, about 9-15 mm long and 6-13 mm in diameter; inner perianth-segments light purple, somewhat reflexed near the tips, acute usually with a darker midregion and paler margins. Stamens pale cream-colored to pale yellow, much shorter than the style, purplish above; stigma-lobes 4-5 narrow reddish-purple to orange-yellow.
Phenology (in habitat): This species blooms in late February to March, rarely later. The small flowers of M. pottsii open about noon or before for at least three days, often 5-6 days, and close at night.
Fruits: Red, clavate about 15 mm long. Fruit development and ripening under natural conditions appear to require one to several months.
Seeds: Black, blackish brown, or dark reddish-brown the surface deeply, nearly oval, and ca. 1 mm long.
Chromosome nunmber: 2n = 22.

Cultivation and Propagation: Mammillaria pottsiiSN|9355]]SN|9355]] comes from an area of summer rainfall and is supposed to be not the most easiest species in cultivation, as particularly sensible to moisture excesses. It will offset profusely.
Soils: Use a an open and free draining mineral compost with little organic matter (peat, humus) that allows therefore roots to breath (as it is rot prone).
Repotting: Repotting every 2-3 years. Use a small pot with good drainage.
Watering: It likes a winter's rest and should be kept completely dry during the winter months. From early spring onwards the plant will begin to grow and watering should be increased gradually until late spring when the plant should be in full growth. Water regularly during the summer so long as the plant pot is allowed to drain and not sit in a tray of water. During hot weather you may need to water the plants more frequently so long as the plant is actively growing. From late summer watering should be reduced to force the plant to go in to a state of semi dormancy, by autumn you should be back in to the winter watering regime. Keep dry with ample airflow in winter (but for outdoors cultivation it is very resistant to wet conditions, too). In the rest period no high atmospheric humidity!! Care must be taken with watering as they tends to become swollen and untidy in growth habit if given too much water and shade.
Fertilization: Feed with a high potassium fertilizer in summer.
Hardiness: Reputedly resistant to frost if kept on the dry side prior to, and during, cold weather (hardy to -5 C ° C, or less for short periods).
Exposition: The plant tolerates very bright situations, if kept too dark they may become overly lush and greener and could be prone to rotting due to over watering. Strong light encourages flowering and heavy wool and spine production, but is likely to suffer from sun scorch or stunted growth if over exposed to direct sunlight during the hottest part of the day in summer. .
Uses: It is an excellent plant for container growing. It always looks good and stays small. It look fine in a cold greenhouse and frame or outdoor in a rockery.
Pests & diseases: It may be attractive to a variety of insects, but plants in good condition should be nearly pest-free, particularly if they are grown in a mineral potting-mix, with good exposure and ventilation. Nonetheless, there are several pests to watch for:
- Red spiders: Red spiders may be effectively rubbed up by watering the plants from above.
- Mealy bugs: Mealy bugs occasionally develop aerial into the new growth among the wool with disfiguring results, but the worst types develop underground on the roots and are invisible except by their effects.
- Scales: Scales are rarely a problem.
- Rot: This species seldom suffer of cryptogamic diseases. Rot it is only a minor problem with cacti if the plants are watered and “aired” correctly. If they are not, fungicides won't help all that much.
Propagation: Direct sow after last frost or usually by offsets (readily available), or occasionally grafted. Seeds (no dormancy requirement) germinate in 7-14 days at 21-27° C in spring, remove gradually the glass cover as soon the plants will be well rooted (ca 1-2 weeks) and keep ventilated, no full sun for young plants! The seedlings should not be disturbed until they are well rooted, after which they can be planted separately in small pots. Cuttings: 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.