Origin and Habitat: This species is found at one location northeast of the city of Guanajuato, Mexico (extent of occurrence and area of occupancy 35 km2).
Altitude range: 1.800 - 2.000 metres above sea level.
Habitat: This species is found on volcanic rock in xerophyllous scrub. Mammillaria duweiSN|8895]]SN|8895]] is known from only one location, has a small population size, and there is a continuing decline due to overcollection and development. The southernmost of the two known subpopulations of this species has declined as a result of collecting over the past 15 years. Currently the total population is estimated at approximately 500 individuals.

• Mammillaria crinita subs. duwei (Rogoz. & P.J.Braun)
• Mammillaria duwei Rogoz. & P.J.Braun
• Mammillaria nana subs. duwei (Rogoz. & P.J.Braun) Pilbeam
• Mammillaria trichacantha subs. duwei (Rogoz. & P.J.Braun) Mottram

• Mammillaria crinita DC.
• Cactus crinitus (DC.) Kuntze
• Chilita crinita (DC.) Buxb.
• Ebnerella crinita (DC.) Buxb.
• Krainzia crinita (DC.) Doweld
• Mammillaria glochidiata var. crinita (DC.) K.Schum.
• Mammillaria glochidiata f. crinita (DC.) Schelle
• Mammillaria aureoviridis Heinrich
• Mammillaria brevicrinita Repp.
• Mammillaria cadereytana Backeb.
• Mammillaria calleana Backeb.
• Mammillaria criniformis DC.
• Chilita criniformis (DC.) Buxb.
• Mammillaria criniformis var. albida DC.
• Mammillaria erectohamata Boed.
• Chilita erectohamata (Boed.) Buxb.
• Ebnerella erectohamata (Boed.) Buxb.
• Mammillaria felipensis Repp.
• Mammillaria gilensis Boed.
• Chilita gilensis (Boed.) Buxb.
• Ebnerella gilensis (Boed.) Buxb.
• Mammillaria glochidiata var. xiloensis Repp.
• Mammillaria moeller-valdeziana Appenz.
• Mammillaria mollihamata Shurly
• Mammillaria puberula Repp.
• Mammillaria pubispina Boed.
• Chilita pubispina (Boed.) Buxb.
• Ebnerella pubispina (Boed.) Buxb.
• Mammillaria pygmaea (Britton & Rose) A.Berger
• Chilita pygmaea (Britton & Rose) Buxb.
• Ebnerella pygmaea (Britton & Rose) Buxb.
• Neomammillaria pygmaea Britton & Rose
• Mammillaria scheinvariana R.Ortega V. & Glass
• Mammillaria crinita subs. scheinvariana (R.Ortega V. & Glass) W.A.Fitz Maur. & B.Fitz Maur.
• Mammillaria schelhasii Pfeiff.
• Cactus schelhasii (Pfeiff.) Kuntze
• Chilita schelhasii (Pfeiff.) Orcutt
• Ebnerella schelhasii (Pfeiff.) Buxb.
• Mammillaria schelhasei Pfeiff. Pfeiff.
• Neomammillaria schelhasii (Pfeiff.) Britton & Rose
• Mammillaria schelhasii var. triuncinata Salm-Dyck
• Mammillaria schelhasei f. triuncinata (Salm-Dyck) Schelle
• Mammillaria tezontle W.A.Fitz Maur. & B.Fitz Maur.
• Mammillaria variabilis Repp.
• Mammillaria zeilmanniana Boed.
• Chilita zeilmanniana (Boed.) Buxb.
• Ebnerella zeilmanniana (Boed.) Buxb.
• Mammillaria crinita f. zeilmanniana (Boed.) Glass
• Neomammillaria zeilmanniana (Boed.) Y.Itô
• Mammillaria zeilmanniana f. albiflora hort.

• Mammillaria crinita subs. duwei (Rogoz. & P.J.Braun)
• Mammillaria duwei Rogoz. & P.J.Braun
• Mammillaria nana subs. duwei (Rogoz. & P.J.Braun) Pilbeam
• Mammillaria trichacantha subs. duwei (Rogoz. & P.J.Braun) Mottram
• Mammillaria crinita subs. duwei f. cristata hort.
• Mammillaria duwei f. cristata hort.
• Mammillaria crinita subs. duwei f. inermis hort.
• Mammillaria duweii f. inermis hort.
• Mammillaria crinita subs. duwei f. monstruosa hort.
• Mammillaria duwei f. monstruosa hort.

• Mammillaria crinita subs. leucantha (Boed.) D.R.Hunt
• Krainzia crinita subs. leucantha (Boed.) Doweld
• Mammillaria leucantha Boed.
• Mammillaria aurihamata Boed.
• Chilita aurihamata (Boed.) Buxb.
• Ebnerella aurihamata (Boed.) Buxb.
• Mammillaria schelhasii var. aurihamata (Boed.) Repp.
• Neomammillaria aurihamata (Boed.) Y.Itô

• Mammillaria crinita f. nana (Backeb.)
• Mammillaria nana Backeb.
• Mammillaria monancistracantha Backeb.
• Mammillaria rawlii hort.
• Mammillaria trichacantha K.Schum.
• Chilita trichacantha (K.Schum.) Buxb.
• Ebnerella trichacantha (K.Schum.) Buxb.
• Mammillaria nana trichacantha hort.
• Neomammillaria trichacantha (K.Schum.) Britton & Rose

• Mammillaria crinita subs. painteri (Rose) U.Guzmán
• Chilita painteri (Rose) Buxb.
• Ebnerella painteri (Rose) Buxb.
• Mammillaria painteri Rose
• Neomammillaria painteri (Rose) Britton & Rose
• Mammillaria crinita subs. painteri f. monstruosa cristata hort.
• Mammillaria painteri f. monstruosa cristata hort.
• Mammillaria crinita subs. painteri f. monstruosa hort.
• Mammillaria painteri f. monstruosa hort.

Description: Mammillaria duweiSN|8910]]SN|8895]] is a small solitary rarely offsetting plants that eventually forms tiny mounds.
Taxonomic Notes: Mammillaria duweiSN|8841]]SN|8895]] is considered a synonym of Mammillaria crinitaSN|8895]]SN|8841]] by Anderson (2001) and by Fitz Maurice (2002). Considered a provisional species by Hunt (1999) and a subspecies of Mammillaria nanaSN|8895]]SN|8910]] by Pilbeam (1999).
Stems: Heads 3,5 to 6 cm in diameter, 2-4 cm high, dark green, soft, globoid, flattened-globose, to shortly cylindrical.
Tubercles: Small, clavate 4-5 mm high, With a woolly axil and little hair.
Central spines: 0-1 or 2 (occasiaonally 4). The long central spine is not present on all the clones, yellowish, hooked, to 8 mm long, pubescent.
Radial spines: 28-36, acicular, thin, white, brownish at base, pubescent, 3,5-4 mm long, interlacing and densely wrapped against the body of the cactus.
Flowers: Funnel-form, less deeply set, yellowish/cream to light yellow, about 20 mm long and in diameter. Inner segments lanceolate, widely spreading, accuminate, style and stigma lobes greenish.
Blooming season: Flowers readily, and for a long period from spring to the early summer.
Fruits: Light red to red, elongated.
Seeds: Blackish brown.

Notes: This plant is a member of the Mammillaria crinitaSN|8841]]SN|8841]] complex (Stylothele Series). Only some authors consider Mammillaria duweiSN|8895]]SN|8895]] to be a good species; the others classify it as M. crinita (e.g. According to Anderson's classification, this species is considered as a synonym of Mammillaria crinitaSN|8841]]SN|8841]])

Bibliography: Major references and further lectures
1) David Hunt, Nigel Taylor “The New Cactus Lexicon” DH Books, 2006
2) Edward F. Anderson “The Cactus Family” Timber Press, 2001
3) Rod Preston-Mafham, Ken Preston-Mafham "Cacti: the illustrated dictionary" Timber Press, 1991
4) John Pilbeam (1999) "Mammillaria The Cactus File Handbook" - page 203.
5) Fitz Maurice, B & Fitz Maurice, W.A. 2013. Mammillaria duwei. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 31 May 2015.

Cultivation and Propagation: Mammillaria duwei is not the easiest to grow of the mammillarias, more rot prone than most and more demanding regarding soil conditions.
Growth rate: It is a small growing, but easily flowering, species that will make clumps given the best conditions.
Soils: It likes very porous standard cactus mix soil.
Repotting: It will need a pot with sufficient depth to allow the tap root. Use pot with good drainage.
Watering: Water regularly in summer, but do not overwater (Rot prone), keep dry in winter. Keep Mammillaria duweiSN|8895]]SN|8895]] in very dry and ventilated place especially in winter.
Fertilization: Feed with a high potassium fertilizer in summer.
Hardiness: Reputedly sensitive to frost , but less so if kept on the dry side prior to, and during, cold weather (hardy to -5° C for short periods). However warmth throughout the year will increase the grower's success (minimum 5° to 8°C during rest season).
Exposition: Outside bright sun, filtered sunlight or afternoon shade, inside it needs bright light, and some direct sun. Subject to sunburn if exposed to direct sun for too long. Tends to bronze in strong light, which encourages flowering and heavy wool and spine production.
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.
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 misting the vulnerable plants every day
- Mealy bugs: Mealy bugs easily they 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.
It is wise to treat your whole collection with a systemic insecticide twice a year in spring and autumn.
- Rot: Rot is only a minor problem with mammillaria 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 (rarely) cuttings. Seeds germinate in 7-14 days at 21-27° C in spring, remove the glass cover gradually as the plants develops and keep ventilated, no full sun for young plants! To make a cutting twist off a branch and permit it to dry out a couple of weeks, lay it on the soil and insert the stem end partially into the soil. Try to keep the cutting somewhat upright so that the roots are able to grow downward.