Cd. Preston et Mo. Hill, The geographical relationships of the British and Irish flora: a comparison of pteridophytes, flowering plants, liverworts and mosses, J BIOGEOGR, 26(3), 1999, pp. 629-642
Aim To compare the wider distribution of the pteridophytes, flowering plant
s, liverworts and mosses recorded as natives of Britain and Ireland, and to
assess the proportion and distribution of species in each group which belo
ng to predominantly extra-European genera.
Location The species native to the British Isles are considered in relation
to their distribution in the Northern Hemisphere, and predominantly extra-
European genera are identified by consideration of the distribution and cen
tre of numerical diversity of the genera worldwide.
Methods A recent classification of the pteridophytes, flowering plants, liv
erworts and mosses into floristic elements is used in a quantitative study
of the distribution of species in the four groups, the patterns of occurren
ce being compared by standardized residuals.
Results Mosses and liverworts have more northerly distributions than the fl
owering plants in the Northern Hemisphere; pteridophytes show an intermedia
te pattern. There are marked differences in the longitudinal ranges of the
groups south of the Boreal biome, with vascular plants tending to be confin
ed to Europe or western Eurasia whereas cryptogams are more likely to occur
additionally in North America or have a circumpolar distribution. The prop
ortion of predominantly extra-European genera is particularly high in the p
teridophytes and the liverworts and in these groups the rich hyperoceanic f
lora of the British Isles is almost entirely composed of species in genera
that attain their centre of diversity in the tropics.
Main conclusions Major taxonomic groups show different distribution pattern
s, reflecting their rates of evolution and powers of dispersal. The floweri
ng plants, as the least mobile and most rapidly evolving group, have a grea
ter proportion of their species in the European and Eurosiberian elements a
nd a higher proportion of species from extra-European genera in the more no
rtherly elements.