This Taxon has various synonyms whit several controversial varieties and subspecies and comprises a multitude of different forms, but where each form is linked to others by populations of plants with intermediate characteristics:

• Ferocactus gracilis H.E.Gates: (subsp. gracilis) has stems up to 1 m in tall and has central spines less than 5 mm wide.Distribution: northern central Baja California.
• Ferocactus gracilis subs. coloratus (H.E.Gates) N.P.Taylor: Usually less than 1 m tall but the widest central spines often exceed 5 mm. Distribution: south of subspecies gracilis.
• Ferocactus gracilis subs. gatesii (G.E.Linds.) N.P.Taylor: Up to 1,5 m tall, and the central spines are curved but not hooked and only 3 mm wide. Distribution: Bahia de los Angeles in the gulf of California (Smith Islands group in the Sea of Cortez)
• Ferocactus horridus Britton & Rose
• Ferocactus peninsulae (F.A.C.Weber) Britton & Rose: (subsp. peninsulae) has 4 central spines, forming a cross. Principal central spine flattened and strongly hooked, flowers over 5 cm long, outer periant segments spatulate. Plant somewhat allways taller than broad. Distribution: Baja California.
• Ferocactus peninsulae f. brevispinus (Chinned type): has very odd chinned ribs.
• Ferocactus peninsulae f. brevispinus cristatus hort.: Crested form.
• Ferocactus peninsulae f. brevispinus hort.: short spined form.
• Ferocactus peninsulae f. brevispinus cv. Artichoke: spineless form remembering in shape an Obregonia denegrii.
• Ferocactus peninsulae subs. santa-maria (Britton & Rose) Pilbeam & Bowdery: has yellow flowers, principal central spine straight or slightly curved. Plant somewhat conical, taller than broad. Distribution: Southern Baja California.
• Ferocactus peninsulae subs. townsendianus (Britton & Rose) Pilbeam & Bowdery: has orange or red flowers, principal central spine strongly hooked. Plant somewhat conical, taller than broad. Distribution: Baja California (Magdalena Plain, Santa Margarita, Magdalena Islands).
• Ferocactus peninsulae subs. viscainensis (H.E.Gates) F.Wolf & R.Wolf: has 4 central spines, forming a cross. Plant to 1,5 m tall and 3 dm wide. Ribs 13-21. Distribution: Baja california norte.