The distribution patterns of native and introduced plants were investigated using floristic surveys of 4 km2 grid squares collected between 1987 and 2008 in lowland England. Variograms were used to compare the autocorrelatory range of 1,293 different species with their native status. Various patterns of spatial distribution were seen in the flora, including species that are highly spatially autocorrelated, through to species whose distribution is spatially uncorrelated at this scale. Almost all native plants showed autocorrelation in their distribution at distances of ,10 km, whereas introduced plants either showed no autocorrelation or over shorter distances than native plants. This difference between native and introduced plants has an important consequence: when biogeographical range size is measured using large (.100 km2) grid squares, as it often is, this can lead to the wrong conclusion that introduced plants occupy more area than native plants with a similar range.