Children (8 direct children, 8 direct and indirect children):
Echinocactus horizonthalonius var. nicholii
Echinocactus horizonthalonius var. horizonthalonius
Echinocactus horizonthalonius subsp. diabolicus
Echinocactus horizonthalonius subsp. nicholii
Echinocactus horizonthalonius subsp. jarmilae
Echinocactus horizonthalonius var. centrispinus
Echinocactus horizonthalonius var. curvispinus
Echinocactus horizonthalonius var. obscurispinus