RETICULATE EVOLUTION IN THE POLYPODIUM VULGARE COMPLEX

Members of the Polypodium vulgare complex are so similar morphological ly and chromosomally that delimiting diploid species and determining t he origin of allopolyploid derivatives has been difficult. Isozyme ana lyses supported published hypotheses of two major diploid lineages wit hin 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 isozy me 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 ther e 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 c ontained isozyme and morphological features suggesting an earlier orig in 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 wer e used to extrapolate patterns of character evolution with greater pre cision. The phylogenetic distribution of ''sporangiasters'' confirmed earlier hypotheses concerning the development of these novel structure s from sporangial initials.