British horticulturalist from Garston, Liverpool. He trained as a Kew gardener (1879) and was employed by the Royal Botanic Gardens as assistant curator (1886-1901) and later curator (1901-1922). He published a number of articles on Arecaceae and other horticultural plants in journals such as Gardener's Chronicle, and wrote a number of horticultural books including Cactus Culture for Amateurs (1889), Orchids (1890) and Rhododendrons and Azaleas (1911). He travelled to South Africa (1887) where he collected bulbous plants and other material of horticultural interest. He is commemorated by Hebenstretia watsonii Rolfe. Not to be confused with the botanical authority Sir William Watson (1715-1787), or William Watson (1832-1912) who collected in India, or several similarly named collectors.