is named for the straight, upward pointing central spines (one per areole), mostly colored maroon-purple and about 1.5 inches long. Other spines also have purplish coloration at the tips; lower parts are grey or white. The plant has 18 to 21 narrow, tuberculate ribs bearing intersecting clusters of 12 to 18 radial spines, lying close to the stem surface, and 1 to 3 centrals, creating quite a dense network of spines that largely hides the green body. Stems may become 13 inches tall, but are usually no more than half this height. Flowers grow from a tight circle right at the top of the plant, blooming in spring and followed by green fruits that become brownish when ripe.
This cactus is quite rare, found in limited areas of south Arizona; near Florence, in Organ Pipe Cactus National Monument, and east of Tucson, from the valley of the San Pedro River to Sahaurita. There are two varieties, with slight differences in flower color and spine dimensions: erectocentrus (around Tucson) and acunensis, in the other locations.