Morphologic and taxonomic relationships of the Psilotaceae relative to evolutionary lines in early land vascular plants

Examination of the fossil record shows that there is no direct evidence regarding the origins and early evolution of the Psilotaceae. Past comparisons betweenPsilotum orTmesipteris and certain fossil plants are reviewed. The major types of early land vascular plants are surveyed in order to demonstrate their basic characteristics and evolutionary trends and to point out the absence of any direct links with the Psilotaceae. Fossil plants of problematical affinities which appear to be important in the early diversification of ferns or plants closely related to ferns are discussed. The nature of stem-leaf relationships of some primitive, extant filicalean ferns and possibly the Psilotaceae is considered in terms of possible similar occurrences among fossil plants.