James Wessell Gerdemann (November 13, 1921 – December 19, 2008) was an American mycologist. He was known for his contributions to the taxonomy of the Glomeromycota, and expertise in arbuscular mycorrhizae. He earned his bachelor and master's degrees in botany at the University of Missouri. His PhD dissertation, titled "The resistance of two tomato varieties to formae of Fusarium oxysporum", was obtained in 1949 at the University of California at Berkeley. The Gerdemann Botanic Preserve in Yachats, Oregon is named after him.