Marshall Conring Johnston (born May 10, 1930) is an American botanist who made several explorations in Mexico and specialized in plants in the family Gesneriaceae.
On those trips he visited the northern Mexican states of Tamaulipas, Nuevo Leon, Coahuila, Durango, and Zacatecas.
From 1972-1974 he made trips to Chihuahua, concentrating on desert flora.
These early 1970s trips resulted in the bulk of his botanic collection.
Johnston was also a professor at the University of Texas at Austin.