Hartmut Geerken (15 January 1939 – 21 October 2021) was a German musician, composer, writer, journalist, playwright, and filmmaker.
As a percussionist, he has collaborated with a variety of free jazz musicians such as Sun Ra, John Tchicai, Sainkho Namtchylak.
In 1979, while living in Afghanistan, Geerken made a study of the ethnomycology of the areas of the country which he visited, co-authoring two papers on the topic.
In the second paper, he describes his discovery of a tradition involving the recreational use of the psychoactive mushroom Amanita muscaria among the Parachi-speaking people of the Shutul Valley.
In the short paper, Geerken's Shutuli informants describe to him how they find solace from the tedium of the long and bitter winters of the Hindu Kush in the bizarre visions caused by the mushroom, one man believing himself transformed into a tree.