A monograph of the fern Genus Microsorum (Polypodiaceae) including an attempt towards a reconstruction of the phylogenetic history of the microsoroids

This revision is a monographic treatment of the fern genus Microsorum (Polypodiaceae). To elucidate the problematic generic delimitation and systematic position of this genus an additional selection of 26 possibly related species was also studied. Most of these related species are traditionally placed in Colysis, Leptochilus, Neocheiropteris, Paraleptochilus, Phymatosorus (‘Phymatodes’), and Podosorus. In order to produce a natural classification an attempt is made to recognize monophyletic groups of species through cladistic analysis. The methods and underlying theories which have been employed are made explicit as much as possible. A suitable selection of intrinsic characters is used for analysis with the computer programs CAFCA, PAUP and HENNIG86. The resulting cladograms are very inconsistent with the datamatrix. They need many ad hoc hypotheses, such as homoplasies, to explain the pattern of distribution of character states among the species. Even when the number of species to be analysed is artificially reduced by using representative species of inferred monophyletic subgroups of Microsorum, the resulting cladograms are to be rejected because of their low consistency indices. The conclusion is reached that the evolution of the microsoroids has resulted in a complex pattern, which cannot be understood sufficiently with the present set of data and available methods. Additional analyses of other characters and species, microsoroids as well as other Polypodiaceae, field observations, cytological and isozyme studies are needed. The results presented here form a good basis for the selection of problematic or promising groups of species. In the absence of an acceptable hypothesis concerning the genealogical relationships among the microsoroids, a temporary formal classification is constructed. Because of this temporary nature of the classification, stability of nomenclature, and recognizability of the taxa, have in this treatment priority over a maximum of phylogenetic information. Thus the classification may contain para- and polyphyletic groups. This results in the recognition of Microsorum in a restricted sense, comprising 20 species (including Dendroconche and Diblemma) and of five other microsoroid genera: Colysis (including Paraleptochilus), Leptochilus (emended), Neocheiropteris, Phymatosorus, and Podosorus. Two species of Microsorum are newly described, namely M. cinctum and M. sopuense, and two newly transferred. Nine species, initially thought to belong to Microsorum, are fully described and included in the key, but are finally classified under one of the other microsoroid genera, resulting in seven new combinations and one new species ( Phymatosorus biseriatus). Many other species of Microsorum (84 names) are excluded but, because of the temporary character of this classification, the formal new combinations, necessary for most of these 84 names, are not formally made.