British botanist responsible for compiling the 20th century flora of the British Isles since and co-editing Flora Europaea (1964). Thomas Tutin was born in Kew, London, where his father, Frank Tutin, worked as a biochemist at the Lister Institute. His sister, Mary Gillick (n⟩e Elizabeth Tutin), became a renowned portraitist who designed the head of the young Queen Elizabeth II on the first coinage of her reign.

Tutin's father and grandfather were both interested in growing plants and Frank Tutin passed on to his son not only his interest but a sizeable private herbarium. Trips to the nearby Royal Botanic Gardens were frequent during Tutin's childhood and by his teenage years (spent in Somerset) he was making his own collections and studying plants under the microscope. He won a scholarship to Cambridge, where he was taught by the engaging Humphrey Gilbert-Carter and became involved in the Cambridge Natural History Society, developing his expertise on sedges and grasses.

With fellow students Heff Warburg, A.P.G. Michelmore, J.A. Kitching and J.W.A.F. Balfour-Browne, Tutin went on an expedition to Madeira and the Azores, afterwards publishing two papers on his findings (despite being only in his second year). It was the first of a number of expeditions in the U.K. and overseas; in 1930 he travelled to Spain and Morocco with fellow botanists Paul Richards and W. Balfour-Gourlay and in 1933 joined an ambitious expedition from Cambridge to British Guiana with the zoologist G.S. Carter and histologist E.N. Willmer. The party based themselves at a former prison settlement on the banks of the Essequibo River and over four months Tutin explored forests and befriended local Indians. Though the trip stimulated his interest in tropical botany, on his return he took up a post at the Marine Biological Association's laboratory in Plymouth to research a disease of eel grass rather than pursuing tropical interests. During this time he described a new genus of Zostera and published two papers on the genus.

In his spare time, he decided to take up the flute and in 1937 entertained fellow passengers sailing to Lake Titicaca on the Percy Sladen Trust expedition. Tutin was the only botanist on the trip and made major contributions to the resulting reports about the Lake's aquatic plants and algae, though he did not enjoy the cool climes. Neither did he enjoy the city environment when he took up a lecturing post at the University of Manchester in 1939, but escaped often to the Lake District and Freshwater Biological Association at Wray Castle. Here he met Winifred Pennington, whom he married in 1942, at which time he was seconded to produce geographical handbooks as part of the war effort. Tutin's task was to survey the fenlands of the north of England for buckthorn (Rhamnus frangula), whose charcoal was used in certain shell fuses.

In 1944 Tutin was appointed Lecturer-in-Charge at Leicester University College, and Professor of Botany in 1947 when the institution received its university charter. He now turned his attentions to taxonomy and began to build up a departmental herbarium with the laboratory steward, Ted Horwood, whose father had co-authored the flora of Leicester and Rutland. It was a meeting with Sir Arthur Tansley in Cambridge, however, that spurred Tutin's decision to compile a modern flora of the British Isles (the last one was J.D. Hooker's 1870 flora, revised 1884). Roy Clapham, Heff Warburg and Paul Richards were brought on board and the 1591-page work was completed by 1948 and published in 1952, immediately becoming the definitive reference work.

In his approach to taxonomy, Tutin wrote about the problems of subjectivity, for example greater attention being given to plants that flower early in the season and little attention being given to characteristics difficult to observe, and argued for subspecies based on morphological differences and geographical range, scrapping the categories of variety and form. He was also interested in evolutionary processes and made a study of annual meadow grass, Poa annua, that demonstrated it originated from Poa infirma and Poa supina.

After the British flora, Tutin's next project (along with colleagues) was the Flora Europaea. He and his team embarked upon the daunting work in 1956 and its five volumes took 20 years to complete (1964-1980), Tutin authoring 1307 species accounts out of 11,047. He was chairman of the editorial committee until his death in 1987. His contributions to plant taxonomy were recognised in 1977 when he was awarded the Linnean Society of London's Gold Medal and he was in 1979 made a Foreign Member of the National Academy of Finland. He was President of the Botanical Society of the British Isles from 1957 to 1961. Thomas Tutin was reputed to have a quiet yet energetic character full of gentle charm and was fond of gardening at his Leicester home, about which he published the piece "Weeds in a Leicester garden" in Watsonia (1973).