RETICULATE EVOLUTION IN THE POLYPODIUM VULGARE COMPLEX

Members of the Polypodium vulgare complex are so similar morphologically and chromosomally that delimiting diploid species and determining the origin of allopolyploid derivatives has been difficult. Isozyme analyses supported published hypotheses of two major diploid lineages within the complex but rejected all but two hypotheses for allopolyploid origins. New hypotheses were erected and the original complex of five diploid species, three polyploid species, and two polyploid cytotypes swelled to seven diploid and seven polyploid species. Subsequent isozyme analyses supported the new hypotheses for allopolyploid origins and continued to affirm earlier hypothesis of two diploid lineages within the complex. At the populational level, isozyme analyses demonstrated that most diploids conformed to Hardy-Weinberg expectations, but there was some indication of inbreeding. A synthesis of the data suggested that glaciation drove allopatric diploids into sympatry and initiated allopolyploid speciation. Two of the allopolyploids had features that suggested a more complex ancestry. Some populations of P. hesperium contained isozyme and morphological features suggesting an earlier origin than the remainder of the populations. Apparent gene silencing in P. vulgare suggested that this largely European species had an earlier origin than others in the complex. Revised phylogenetic hypotheses were used to extrapolate patterns of character evolution with greater precision. The phylogenetic distribution of ''sporangiasters'' confirmed earlier hypotheses concerning the development of these novel structures from sporangial initials.