Evolutionary Patterns and Processes in Ferns

Abstract

The sole important development in fern cytological technique has been the development of a variety of squash methods for the study of fern chromosomes in somatic tissues. This chapter reviews the evolutionary patterns and processes in ferns. The fossil record of the polypodiaceous ferns in Mesozoic era and tertiary period are also reviewed. The Thelypteridaceae is a large and axonomically difficult family, whose classification is in an only partially resolved state, whereas, the Dryopteridaceae is a large and morphologically diverse but cytologically remarkably uniform family. The existence of a great natural group of genera, the Adiantaceae is also presented in the chapter. The cytology of some of the ancient ferns such as Psilotales, Ophioglossales, Marattiales, and Osmundales are discussed. The information necessary for evaluation of the contribution that cytology can make towards a true phylogenetic classification of the ferns is presented here showing the basic chromosome number or numbers determined for each genus. The different types of polyploidy found in ferns namely autopolyploidy, allopolyploidy, segmental alloploidy and autoallopolyploidy, and their occurrence in different species complexes are also discussed. The systematic and geographical distribution of polyploids, irrespective of their genetic nature, is also reviewed. © 1977 Academic Press Inc. (London) Ltd.