AbstractRadial growth of cushions ofLeucobryum glaucumwas studied by the crankwire method over two years in an oakwood at Mill Pond, Easthampstead, Berkshire. At this siteL. glaucumis the dominant ground flora species on acidic peat and forms some exceptionally large cushions (largest 2 m long, 1.5 m wide, 55 cm high). Growth was unrelated to initial cushion radius and proceeded at a similar rate on all faces of the cushions (overall average, 9.1 mm yr-1). Estimates of the age of the largest cushion range from sixty to eighty-four years depending on the radius measurement used. Growth rate was highest during the summer and autumn. It was unrelated to variations in precipitation but correlated strongly with air temperature, particularly accumulated temperatures (day-degrees) above 5°C. Evidence is discussed in support of the proposal thatL. glaucumis relatively thermophilic. The large cushions at Mill Pond probably result from a combination of favourable circumstances including the warm southern locality, the moist acidic soils, a humid sheltered microclimate and protection from disturbance.