«Piper in the Woods» by Philip K. Dick

Piper in the Woods is a science fiction short story by Philip K. Dick, first published in 1953.
Earth maintained an important garrison on Asteroid Y-3. Now suddenly it was imperiled with a biological impossibility-men becoming plants!
Henry Harris, a military psychologist at a garrison on Earth is puzzled by a case of a soldier who returns from the asteroid Y-3, and claims that he's a plant. When several more men return from Y-3, each thinking they're a plant, Harris travels to the asteroid to solve the puzzle.
Piper in the Woods was first published in Imagination: Stories of Science and Fantasy February 1953.
Philip Kendrick Dick (1928-1982) was an American science fiction author. Dick explored sociological, political and metaphysical themes in novels dominated by monopolistic corporations, authoritarian governments, and altered states.
In addition to 44 published novels, Dick wrote approximately 121 short stories, most of which appeared in science fiction magazines during his lifetime.
Although Dick spent most of his career as a writer in near-poverty, ten popular films based on his works have been produced, including Blade Runner, Total Recall, A Scanner Darkly, Minority Report, Paycheck, Next, Screamers, and The Adjustment Bureau.
In 2005, Time magazine named Dick one of the one hundred greatest English-language novels published since 1923. In 2007, Dick became the first science fiction writer to be included in The Library of America series.