FRANCIS ROSE could fairly be described as the doyen of British field botany. His knowledge of the flora of western Europe had few rivals and his reputation as a field botanist was legendary. What distinguished him was that to him “flora” meant precisely that; the sum total of the flowering plants, ferns, mosses, liverworts and lichens. He was equally at home with the tiny encrusting lichens adorning the megaliths of Stonehenge as with the lady orchids of his beloved North Downs woods.

Born in South London in 1921, Rose was first awakened to an interest in botany by a naturalist grandfather who took him for country walks at the age of 5. Unfortunately, there was no biology at his Roman Catholic school, Xavier College. Nevertheless, he entered the University of London in 1938, first at the Chelsea Polytechnic and then Queen Mary College, from where he graduated in botany in 1941.

In 1947, after wartime work testing explosives and a stint teaching engineering science at Gravesend Technical School, he arrived at Sir John Cass College as lecturer in botany. Two years later he moved to Bedford College where he stayed for the next 15 years.

Here he developed his early research interest in the ecology of bogs and fens, for which he was awarded his PhD in 1953 for his thesis, A Survey of the British Lowland Bogs. He was later to develop this work with the assistance of a young research student called David Bellamy.

Rose was an inspirational teacher. A day in the field was worth hours in the lecture theatre. His knowledge was encyclopaedic, and he had the gift of making even the commonplace exciting. No matter on how many previous occasions he would have expounded on a particular plant each reacquaintance would be infused with the zest of novelty. He had an extraordinary “eye for habitat”, which enabled him to predict the occurrence of rare species from the nature of the ground with an astonishing (and sometimes infuriating) degree of accuracy.

His Wild Flower Key, first published in 1981 and recently revised by Clare O’Reilly, is one of his most valuable legacies. The fruits of more than 50 years’ experience of teaching students in the field, uniquely, it enables plants to be identified by habitat when not in flower and is widely recognised as the best field guide in the business. This was followed in 1989 by the beautifully illustrated Colour Identification Guide to the Grasses, Sedges, Rushes and Ferns of the British Isles. The Flora of Hampshire (1995), which he co-authored with Lady Anne Brewis and Paul Bowman, is widely regarded as the paradigm of local floras.

In 1964 Rose moved to King’s College London as senior lecturer in biogeography. He was appointed University Reader in 1975, a post that he occupied until his retirement in 1981.

From the mid-1960s he became increasingly involved in the use of plants as bioindicators of past and present environmental conditions. With David Hawksworth he was one of the first to demonstrate the value of lichens growing on tree trunks as sensitive indicators of specific levels of atmospheric sulphur pollution. He also showed that forest lichens were not sensitive only to air quality. Certain species were to be found only in ancient undisturbed woodlands, which enabled him to construct a series of “indices of ecological continuity”, a technique that he later extended to higher plants.

This work had important consequences for our interpretation of the nature of what the botanist and landscape historian Oliver Rackham has termed the “wildwood”, the presumed pre-agricultural forest cover of Britain.

The richest sites were those with isolated ancient trees set amid pasture grassland, such as parts of the New Forest, rather than continuous closed woodland. In this he anticipated by more than 25 years the recent theories of Franz Vera on the role of grazing animals.

Rose was deeply committed to the cause of conservation. He was a keynote speaker at the seminal conference held at the London Zoo in 1958 which established the county naturalists trusts in southeast England and was chairman of the Kent Trust, 1959-65. The files of English Nature contain dozens of his reports that resulted in the original notification of a substantial proportion of all of the sites of special scientific interest in southern England. He was a founder member of Plantlife, and campaigned vigorously for the proposed South Downs national park until shortly before his death.

The fruits of his fieldwork reside in a collection of about 200 notebooks, commencing in 1944, and containing an estimated 250,000 individual records. These, together with the bulk of his herbarium, are held by the National Museums and Galleries of Wales. In order to ensure that this unique archive is widely available, the notebooks have now been transcribed and computerised by the Sussex Biodiversity Records Centre.

Rose was an active member of the Botanical Society of the British Isles, the British Bryological Society and the British Lichen Society and elected an honorary member of all three, the only British botanist to be so honoured. He was appointed MBE in 2000 and received the Wildlife Trust’s Christopher Cadbury Medal in the following year.

In 2003 the Royal Botanic Gardens, Kew, established the Francis Rose Reserve at Wakehurst Place, the first nature reserve in Europe to be dedicated to mosses, liverworts, lichens and ferns. His name is celebrated in two species of lichens; Phyllopsora rosei and Porina rosei.

A larger-than-life character with a genial disposition and a sometimes irreverent sense of fun, Rose was great company both in the field and in the pub afterwards. Many of the apparently apocryphal stories told of him were in fact true. If failing light stopped play on a cold December afternoon he would indeed bring out the matches to illuminate some micro-moss in a gloomy ravine. The only effect of rain on the business in hand was to provoke him into reversing his pipe to prevent the fire from being extinguished.

He married, in 1943, Pauline Wendy Arnup. She survives him, together with their daughter and three sons.

Francis Rose, MBE, botanist and conservationist, was born on September 29, 1921. He died on July 15, 2006, aged 84.