Echinocactus horizonthalonius ssp nicholii

Echinocactus horizonthalonius ssp nicholii name was introduced by Benson for Arizona plants. This is somewhat isolated population (or group of populations), located West of Tucson, with plants virtually indistinguishable from the others belonging to the species. In fact, there are recently discovered Mexican locations where plants do show noticeable different features. Benson had given these plants the special taxonomic treatment based exclusively on the fact that the very old plants here are large and have thicker stems, compared to New Mexico and Texas plants.