William Purdom (10 April 1880 – 7 November 1921) was a British plant explorer sent by Veitch and the Arnold Arboretum of Harvard University to the northern provinces of China in 1909. He collected and photographed plants for the Arboretum along China’s Yellow River for three years, 1909–1911. He was appointed Inspector of Forests to the Chinese Government. Rhododendron purdomii was named after him at the Arnold Arboretum. He and Belgian horticulturist J. Hers planned to edit Flora of China, but the plan was halted by the dismissal of the department. Later, Hers wrote Directory of Longhai Area Plants.
In 1914 Purdom and a companion Reginald Farrer set out on an ambitious expedition to Tibet and the Province of Kansu province of North-west China. These two years of exploring and plant collecting are described in Farrer's 'On the Eaves of the World' (2 vols) (1917), and Farrer's posthumous 'The Rainbow Bridge (1921).
The standard author abbreviation Purdom is used to indicate this individual as the author when citing a botanical name.