Mammillaria gueldemanniana ( Backeberg )

First description by Backeberg, Beitr. Sukk. pflege 1941: 1:57
Body: Strongly clumping, cylindrical to columnar, somewhat sunken apex, stems grey-green, spines nearly obscuring the stem, 10 - 20 cm high and 3 - 5 cm in diameter.
Roots: Fibrous.
Sap: Without latex.
Tubercule: Cylindrical, closely set, firm, keeled ventrally, 7 - 12 mm long and 5 - 8 mm wide.
Axil: Mostly naked.
Radial spine: 12 - 22, needle like to bristle like, straight, smooth, spread out horizontally, white with brown tip.
Central spine: 1 - 4, mostly 1, needle like, one hooked, smooth, brown to black, 2 - 14 mm long.
Flower: Funnelform to broad funnelform, 18 - 25 mm long and 16 - 35 mm in diameter, carmine pink.
Fruit: Club-shaped, scarlet - red, 10 - 25 mm long and 4 - 7 mm wide. Ripens about one year after flowering.
Seed: Spherical, black, 1 mm long and 0,8 mm wide, ventral hilum. Selfsterile.
Habitat Substrate: In green valleys, in sandy soil with a bit of humus .
Geographic Distribution: Mexico, Chihuahua near Batopitas; Sonora near Navajoa; Sinaloa near El ranchito. Altitude 200 - 1300 m.
Bibliography: Mbl voor liefh. van cact., vetpl. en kamerpl., 4: 63 - 64, (1992). Reppenhagen: Die Gattung Mammillaria p110; Maddams 'Our search for succulents in Sonora (part 4)' in Journ. Mam. Soc. 10: 34-35.(1970)

Additional bibl.: Reppenhagen: Die Gattung Mammillaria p110; he does mention Mam. guirocobensis Craig (Mam. Handb. 220. 1945) as synonymous. He also mentions Maddams 1970 'Our search for succulents in Sonora (part 4)' in Journ. Mam. Soc. 10: 34-35.

Pirex
In Flanders Fields