Pelecyphora aselliformis is a rare and very slow growing cactus, it is usually found grafted and "own roots" specimens are highly valued.

Description: Small clustering cactus
Stem: Spherical to shortly cylindrical, 5-10 cm tall, 2-5 cm in diameter. The stem in young plant is quite different, very thin, pencil-like or clavate.
Tubercles: Laterally flattened, elongated, arranged in spirals;
Areoles: Oval shaped areoles. Areoles in this species are clearly dimorphic, much as in the mammillarias, but the vestigial groove is reminiscent of Coryphantha and related genera.
Spines: 40 to 60 pectinated.
Flowers: Pink to violet flowers with lighter outside petals, 2 - 3.5 cm in diameter. The floral buds are acuminate and appear on the apex.
Fruit: Dry, papery.
Seeds: Brown, curved and reticulate.
Blooming season: It normally flowers from February till October, but only if the sunlight is strong enough.

NOTE: This species is closely related to Encephalocarpus strobiliformis. All evidence (the external features such as floral, fruit, and seed morphology, but also the internal structure, including tubercle and areole development, the anatomy of surface layers of mature tubercles, the structure of crystals in the ground tissues, and features of tracheary elements etc.) shows that the two plants are congeneric.
 

The spines are pectinated and look like the Sowbugs or woodlouse (Oniscus asellus) from which the species name.

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The stem in young plant is quite different, very thin, pencil-like or clavate.

Scientific Name: Pelecyphora aselliformis  Ehrenberg 
Published in: Botanisches Zeitschrift 1:737 (1843)

Origin:  Mexico (San Luis Potosí - around the city of San Luis Potosí.)

Habitat: This species is found in grit, at over 1800 meters in altitude, and receives little water in summer and none in winter. Plants grow in the shade of bushes and don’t get direct sun at midday.

Synonym:

• Ariocarpus aselliformis (Ehrenberg) Web. in Bois, Dict. Hort. 931 (1898).
• Mammillaria aselliformis (Ehrenb.) H.P.Kelsey & Dayton 1942
  Mammillaria asellifera Monville ex Weber in Bois, Dict. Hort. 931 (1898);
• Anhalonium aselliforme F.A.C.Weber. in Bois, Dict. Hort. 931 (1898);
  Pelecyphora aselliformis grandiflora Haage Jr., Kakt. Kultur 2a:206 (1900)].

Common name: Peyotillo, hatchet cactus, woodlouse cactus.

Etymology: From the Greek "pelekus" (hatchet) and "phoros" (bearing), referring to the shape of the tubercles.

Conservation status: Listed in CITES appendix I

A young plant grafted to speed up the growth
 

Seedlings at the base of an old plant in the growing pot.
Mature specimens function as  nurse plants and creates an environment that is less severe for young seedlings growing underneath it to survive in a harsh desert environment.

Cultivation: It’s a relatively easy species to cultivate, but very slow growing. Needs a very well drained soil.  Requires strong sun to part sun to develop good spinal growth and waterings should be rather infrequent, to keep the plant compact and not become excessively elongated and unnatural in appearance. Keep dry in winter, or when night temperatures remain below 10° C (but some people give this plant a light monthly watering to prevent the drying and shedding of the lower tubercles.) it is hardy to -4°C for a short period. Assure a good ventilation.

Propagation: It can be reproduced both by seeds and cuttings, but it is often grafted because difficult and slow to grow on its own roots. Older specimens shoot tillers from under tubercles, so they can be grafted, which is a much easier way of propagation than sowing. Young seedlings are tiny and they need several years to reach adult size, and require very careful watering.
 

This species is a rarity every cactus impassioned would like to have. The appeal lies in the peculiarly-shaped tubercles and showy flowers, plus the challenge of growing it successfully.

Photo of conspecific taxa, varieties, forms and cultivars of Pelecyphora aselliformis:

• Pelecyphora aselliformis
• Pelecyphora aselliformi cristata
• Pelecyphora aselliformis mostruosa cristata