Latin stŏlo (stem stŏlōn-) ‘stolon, runner’ + Latin –fer ‘carrying’. Marshall: “Plant simple; in colonies, connected by stoloniferous roots just below ground level”.
The original epithet stoloniferus is often corrected to stolonifer, but the suffix –fĕrus, though uncommon, was in fact used in Latin (e.g. dĕĭfĕrus, infructĭfĕrus).
Maarten H.J. van der Meer (2022 Aug 17). Echinocereus stolonifer. Dictionary of Cactus Names. Retrieved from https://www.cactusnames.org/echinocereus-stolonifer