There are (at least) two "inermis"es in Echinocereus, and many more elsewhere. Those two are
E. troglochidatus f. inermis (formerly E. coccineus)
Mojave Hedgehog Cactus (Echinocereus triglochidiatus subsp. mojavensis 'Inermis')
E. inermis (aka E. knipellianus)
Peyote Verde (Echinocereus knippelianus)
In neither case are the stems always spineless all the time. The name is meant more in a relative sense, I think, compared to their extra-spiny close relatives. Fewer and wimpier spines, if not necessarily none at all.
This tracks with other such identifiers, like esculenta and edulis ("edible") which I most definitely would not ever take in a literal sense without some real confirmation. In the case of Euphorbia esculenta, for example, the name has something to do with animals grazing on it I think, and not humans turning it into sautéed vegetables. However in the case of Dudleya edulis, I can safely say the leaves are most delicious and best consumed fresh off a plant a month or two after the winter rains.
Perhaps a better Latin name for the not-quite-spineless cacti is subinermis (like almost spineless) and yes indeed there is also an E. subinermis in the mix. I believe Donald has one of those, or had one, and his plant inspired me to get one of my own. Which is not spineless but close. Giant yellow flowers.
Alicoche (Echinocereus subinermis subsp. subinermis)
