Arthur Roy Clapham (1904 -1990), Professor of Botany at Sheffield from 1944 to 1969, was a significant figure in botanical science both at home and internationally. Born in Norwich, and educated at the City of Norwich School, he gained a double first specialising in botany at Downing College, Cambridge, in 1922. After several years of research in plant physiology at Cambridge he moved in 1928 to Rothamsted Agricultural Experimental Station as a crop physiologist. In 1930 he went to Oxford, studying with the encouragement of the father of British plant ecology, A.G. Tansley, and playing a leading role in The Biological Flora of the British Isles, launched in 1940. He became editor of The New Phytologist in 1931, and served that journal for three decades. When he moved to Sheffield in 1944 his declared aim was to build up a research school centred on the Biological Flora, with its synthesis of information. The Unit of Grassland Ecology was founded in the Department in 1961 (later the Unit of Comparative Plant Ecology). The early 1950s saw the start of the detailed mapping of British plants on a 10-kilometre square base, initiated by Clapham (the model now adopted for fauna), and in 1952 the old Bentham and Hooker Flora was superseded as the standard work by the widely-acclaimed Flora of the British Isles by Clapham, T.G. Tutin and E.F. Warburg. As well as a wide range of scientific publications Clapham also published work of general interest, such as his Oxford Book of Trees of 1975.