Philip K. Dick: Veg

Dr. Henry Harris has been called to the outpost for asteroid Y-3, humanity's first line of defense against a vast, strange galaxy, because there's a strange infection growing among the soldiers of the outpost: they think they're turning into plants.

Adapted from "Piper in the Woods" by Philip K. Dick: (Warning, link NSFW as it contains a drawing of a nude alien) https://myths.link/piper