| Author||R.E. Holttum|
|Journal||Flora Malesiana - Series 2, Pteridophyta|
|Abstract||CARL FREDRICK ALBERT CHRISTENSEN (1872-1942) was the founder of modern fern taxonomy. To appreciate the scope of his work, it is necessary to understand the confusions of thought on the subject which persisted through the 19th century and were still evident in the summary prepared (by DIELS) for ENGLER & PRANTL’S Pflanzenfamilien in 1899. CHRISTENSEN’S first great work was his Index Filicum (1905-6) in which he listed all known fern binomials and also relegated many to synonymy. In the main he adopted the classification and nomenclature of DIELS. While preparing the Index he came to realize that many generic concepts accepted in the Index were unnatural or confused. This was especially evident in the great complex of species which he listed under the name Dryopteris. He next made a study of the tropical American species of that complex, and in so doing discovered how to separate them into natural groups (1913, 1920). At the time I first made contact with him (about 1925) he had begun to study ferns of the Old World tropics. I maintained a regular correspondence with him from 1925 to 1940, and sent him many specimens for identification. I also met him in Europe in 1930, 1934 and 1938 and had long discussions with him. I benefited from his wisdom also indirectly through the publications of R. C. CHING, who studied with CHRISTENSEN in 1929-1932 and applied CHRISTENSEN’S ideas to Chinese and Indian ferns in an important series of papers in the 1930s. CHRISTENSEN’S identifications of my collections and his comments upon them were the basis on which my own work was built; in the present Series of Flora Malesiana I have tried to extend his methods and his ideas to a much wider range of species than he could have encountered. To him I am profoundly grateful, and I am concerned also to acknowledge my debt, through him, to some perceptive earlier workers, notably G. H. METTENIUS and JOHN SMITH.|
The objectives of any scheme of biological classification are to show natural relationships and to provide a means for the identification of individual organisms. It has sometimes been suggested that only the latter objective is important, and that a ‘practical’ scheme is all that is needed. The history of fern classification has shown that artificial schemes, made without thought as to relationships, do not work; and distribution-maps based on such schemes are meaningless. Fern classification as understood today should be based not only on gross-morphological characters but also on microscopical characters pertaining to the fern's anatomy, indument, spores, gametophytes, etc., and on cytotaxonomy.
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