Whittaker's collection at Kew Gardens is from his trip to Australia and from ports where he stayed shortly during the way home. He also left a collection of 2,200 pressed plants in 79 volumes, mostly from Derbyshire, which are now held in the herbarium at Derby Museum and Art Gallery. They provide important evidential samples for local studies on the flora of Derbyshire. Due to his participation in botanical exchanges clubs, there are now Whittaker samples in many UK museum collections, including those at Bolton, Birmingham, Gloucester and Manchester. The Wisbech and Fenland Museum also has a small collection.