Pteridophyte richness in the NE Iberian Peninsula:: biogeographic patterns

The richness and coexistence of pteridophyte species were studied at the mesoscale level in the NE Iberian Peninsula (Catalonia and Andorra) using a grid system with 10x10 km cell-size. The number of pteridophytes, the number of monolete and trilete ferns (two spore patterns), and the number of polyploid and diploid ferns were studied in 371 of such units. The results suggest: (a) a significant relationship of pteridophyte species richness with higher-taxon richness (genera, family, order, class); (b) a significant relationship between pteridophyte richness and maximum altitude (positively related), bedrock type (higher richness in siliceous types), and distance to the coast (interacting with altitude); (c) a significant positive relationship of monolete/trilete ratio with altitude (in the study area) and with latitude (at the European scale); (d) a significantly higher polyploid/diploid ratio for monolete ferns than for trilete ferns, and a significant relation of this ratio with altitude. We conclude that at the scale studied, the distribution of pteridophyte richness is mainly related to terrain and climate parameters and that the monolete/trilete pattern may be explained by the higher polyploidy rate and better migration capacity in monolete species.