A CHROMATOGRAPHIC STUDY OF RETICULATE EVOLUTION IN THE APPALACHIAN ASPLENIUM COMPLEX

SMITH, DALE M. and DONALD A. LEVIN. (U. Illinois, Urbana.) A chromatographic study of reticulate evolution in the Appalachian Asplenium complex. Amer. Jour. Bot. 50(9): 952-958. Illus. 1963.-The reticulate relationships of the members of the Appalachian Asplenium complex were studied by means of paper chromatography. Substances could be observed with ultraviolet light in the presence of ammonia vapor in all the taxa of the complex. The diploid species (A. montanum, A. platyneuron and A. rhizophyllum) had characteristic biochemical substances. Interspecific hybrids and/or their allotetraploid derivatives showed a complete complementation of all the substances of their known or presumed diploid ancestors. A combination of all the substances of the 3 diploids was found in the hybrids A. X kentuckiense and A. X gravesii. The results agree in all respects with the concept of reticulate evolution in the group which was advanced by Wagner on the basis of comparative morphology, hybridization and karyology. QUESTIONS of the origin and taxonomic treatment of polyploid taxa have received much attention, but the difficulties involved in carrying out detailed morphological comparisons, cytogenetic analyses, crossing experiments, and other pertinent investigations are so great that the ancestry of a polyploid taxon is rarely ever fully established. Furthermore, with respect to some polyploids, the data often do not allow one to differentiate between closely related members of a species group, any one of which might logically be considered ancestral to a particular polyploid. The use of paper chromatography of certain biochemical constituents to study interspecific hybridization may be extenided to an investigation of the problems associated with polyploidy, sinice polyploids are frequently of hybrid origin. An important generalization emerging from biochemical studies of hybridization is the idea of complementation of species-specific constituents of the parental species in interspecific hybrids (Alston and Turner, 1962); that is, the detectable substances of the parental species are found together in their hybrids. The implication of this fact for the study of polyploidy is that if one knows what substances occur in the diploid species which are presumed basic to a polyploid series, it should be possible to postulate the ancestry of a polyploid species on the basis of its complement of speciesspecific chemical constituents. The Appalachian Asplenium complex (Wherry, 1925; Wagner, 1954) offers an excellent opportunity to test the validity of a chemical approach 1 Received for publication March 20, 1963. 2 The authors wish to express their thanks to Professor Warren H. Wagner, Jr., of the University of Michigan, for many helpful comments and for supplying material of A. ebenoides, A. x wherryi, and A. x gravesii, and to Professor Ralph E. Alston, of the University of Texas, for many helpful suggestions and comments during an earlier phase of this work. Thanks are also due those collectors whose specimens were used in this study, especially Mr. T. R. Bryant and Mr. D. E. Tate. to the study of polyploidy. The interrelationships of these ferns have been worked out in great detail by more conventional studies. Wagner (1954) postulated that Asplenium montanum, A. platyneuron, and A. rhizophyllum (Camptosorus rhizophyllus) are the diploids basic to this complex, and genomic allotetraploids derived from these species are A. bradleyi (A. montanum-platyneuron), A. pinnatiJidum (A. montanum-rhizophyllum), and A. ebenoides (A. platyneuron-rhizophyllum). The latter taxon is known in the form of a sterile diploid hybrid as well as the fertile allotetraploid. Only tetraploids are known of A. bradleyi and A. pinnatifidum. In addition to the plants mentioned above, there are several natural and artificial hybrids which provide further insight into this complex (Darling, 1957; Smith, Bryant and Tate 1961a,bc; Wagner, 1954, 1956, 1958; Wagner and Boydston, 1958, 1961; Wagner and Darling, 1957; Wagner and Whitmire, 1957). Named hybrids include A. X gravesii (A. bradleyi X pinnatifidum), A. X kentuckiense (A. pinnatifidum X platyneuron), A. X trudellii (A. montanum X pinnatifidum), and A. X wherryi (A. bradleyi X montanum). Of this group, A. X kentuckiense is especially interesting since it combines equal numbers of chromosomes from each of the diploids (Smith et al., 1961c). Other known natural and/or artificial hybrids between members of this complex are A. bradleyi X platyneuron, A. ebenoides X platyneuron, A. ebenoides X rhizophyllum, and A. ebenoides X pinnatifidum. Most of these taxa were available to us, and the collection presented an unusual opportunity to test a number of facets of biochemical systematics as well as an opportunity to gain new insight into the problems of the interrelationships of the Appalachian spleenworts. First, it was essential to know whether or not these taxa could be identified by means of chromatography. Individual variation could be studied from population samples and by comparing individuals from one population to