This member of the Cactaceae family was given this name by Nathaniel Lord Britton and Joseph Nelson Rose in 1909. It is found in Mexico and southern U.S.A., growing in grit with little water and some to lots of sun. The caudex will grow up to 30 centimetres or more, the branches will reach for up to two meters. The large white flowers will appear at night.
The genera name from pene; 'thread' and Cereus; another member of the Cactaceae family, as to plant's form. The species name after Josiah Gregg, 1806-1850, an US-American cactus collector. Photo by Shannon Henke, Swbiodiversity.org.

