[Wikipedia] Taxonomy: Ferocactus viridescens was first discovered in 1836 by Thomas Nuttall, an English botanist and naturalist. Nuttall had arrived in San Diego aboard the hide ship Pilgrim, and stayed in the harbor for three weeks while he waited for a Bryant and Sturgis ship to sail him back to Boston.[5] From Nuttall's specimens, John Torrey and Asa Gray described Echinocactus viridescens in 1840.[6] The Latin specific epithet viridescens means "turning green".[7] Nathaniel Lord Britton and Joseph Nelson Rose later reclassified the species under the genus Ferocactus in 1922, creating the current combination. (link added by Mary Ann Machi)