PHYTOGEOGRAPHIC PRINCIPLES AND THEIR USE IN UNDERSTANDING FERN RELATIONSHIPS

Biogeographical inferences depend on, but must also be used to construct, classifications. In practice, we apply a knowledge of biogeographical principles or tendencies, established through weight of examples from many organisms, to questions of relationship. These principles state that taxonomic affinity is often correlated with or predicted by geographic proximity, similar ecological needs, climatological affinity and historical or geological factors. Certain phenomena, such as glaciation and continental drift, have resulted in repetitive distribution patterns. We also apply a knowledge of fern biology when evaluating distributional data. For example, because dispersal of spores is generally greater than of seeds, fern genera and species tend to be more widely distributed and show less endemism than seed plant taxa. Taxonomic gaps caused by extinctions may be less noticeable in ferns.