Origin and Habitat: Arizona: Pima, Pinal, Maricopa and Yuma counties. (Southwestern U.S.A., Northern America)
Type Locality: Pima County, north side of the town of Ajo.
Habitat and ecology: Unlike the type F. wislizeni subsp. wislizeni that is found mostly on sandy and rocky soils, the typical habitat of F. wislizeni subsp. ajoensis is the grassland in the flat basin floors of the Sonoran Desert dominated by silts and clays. It is associated with numerous cacti and succulent species.

• Ferocactus wislizeni subs. ajoensis Fencl & Kalas
• Ferocactus wislizeni var. ajoensis Fencl & Kalas

• Ferocactus wislizeni Britton & Rose
• Echinocactus falconeri Orcutt
• Echinocactus wislizeni Engelm.
• Ferocactus wislizeni var. albispinus (Toumey) Y.Itô
• Echinocactus wislizeni var. albispinus Toumey
• Echinocactus wislizeni f. albispinus (Toumey) Schelle
• Ferocactus wislizeni var. falconieri (Orcutt) Y.Itô
• Ferocactus wislizeni var. phoeniceus (R.E.Kunze) Y.Itô
• Echinocactus wislizeni var. phoeniceus R.E.Kunze
• Echinocactus wislizeni f. phoeniceus (R.E.Kunze) Schelle
• Ferocactus phoeniceus (R.E.Kunze) Orcutt
• Ferocactus wislizeni var. rosea Y.Itô

• Ferocactus wislizeni subs. ajoensis Fencl & Kalas
• Ferocactus wislizeni var. ajoensis Fencl & Kalas

• Ferocactus wislizeni subs. herrerae (J.G.Ortega) Pilbeam & Bowdery
• Ferocactus herrerae J.G.Ortega
• Ferocactus wislizeni var. herrerae (J.G.Ortega) N.P.Taylor

• Ferocactus wislizeni subs. tiburonensis (G.E.Linds.) Pilbeam & Bowdery
• Echinocactus wislizeni subs. tiburonensis (G.E.Linds.) Felger
• Ferocactus tiburonensis (G.E.Linds.) Backeb.
• Ferocactus wislizeni var. tiburonensis G.E.Linds.

Description: Ferocactus wislizeni subsp. ajoensis is an infraspecific name used to indicate a very long spined form of Ferocactus wislizenii. It is distinguished from the type subspecies of F. wislizeni by columnar, slender body, longer, denser and more robust spines and earlier and longer flowering period during the summer months. This subspecies will almost certainly not be recognized by more strict taxonomists. But it's interesting and definitely look different from the usual wislizenii.
Derivation of specific name: The specific name ajoensis refers to the town of Ajo, the type locality of this species.
Stem: Solitary, columnar, slender, up to 1.5 m tall, and 30-40 cm in diameter, epidermis green.
Ribs: 20-30.
Areoles: More or less woolly.
Spines: Variable, purple, grey to nearly white. Central spines variable, very strong, straight, hooked, 4.4-12 cm long. Radial spines 8-10, unequal, needle-shaped, up to 5 cm long.
Flowers: Funnel-shaped, variable, whorled around the apex, red, orange, 40-50 mm long and broad, petal with darker median stripes.
Blooming season: May to August, depending on local and cultural conditions.
Fruits: Ovate, fleshy, yellow, 36 mm long, 25 mm wide.
Seeds: Dark brown to black, 1.9-2.3 mm long.

Bibliography: Major references and further lectures
1) Ferocactus wislizeni subsp. ajoensis in: Kaktusz-Vilag web: http://www.kaktuszgyujtok.hu/kvo/2014-6/ferocactus-wislizeni-subsp-ajoensis-egy-uj-alfaj-delnyugat-arizonabol
2) Ferocactus wislizeni subsp. ajoensis in: CactiGuide.com web: http://www.cactiguide.com/forum/viewtopic.php?t=28651
3) Ferocactus wislizeni subsp. ajoensis in: AGAVACEAE NOLINACEAE CACTACEAE web: http://fhirt.org/ferocactus/f_wislizeni_ajoensis.php
4) Fencl & Kalas Bradleya 31. 7. 2013.