Taxonomic revision of fern Microsorum punctatum (L.) Copel. complex (Polypodiaceae)

Abstract

Microsorum punctatum (L.) Copel. is a widespread species. It is found from sea level to about 2,800 m altitude and has its distribution in the palaeotropics and subtropics. At present, the taxonomic status and boundary of this species is still uncertain due to the great variation in many characters. This variation does not match with previous systematic treatments. So, this species group was proposed as a species complex and worth investigating. In order to investigate this doubtful taxon, more than 1,500 specimens were studied. Based on morphological and anatomical characters, M. punctatum complex can be divided into 8 taxa. This result rather corresponded with the results of cluster analysis and canonical discriminant analysis performed on 707 herbarium specimens deposited at BCU, BKF, BM, K, B, L and P. Twenty three quantitative and 35 qualitative characters were employed. Cluster analysis revealed the separation of the taxa in the species complex into eight groups. The eight-cluster grouping is discussed. From a canonical discriminant analysis using the eight-cluster grouping as priori groups, it can be concluded that M. siamense, M. thailandicum, M. membranaceum, M. glossophyllum and M. musifolium are obviously distinct taxa, while specimens of M. steerei and M. whiteheadii mixed together and should be proposed as the same species. Likewise, the specimens of the previous recognized species as the other 10 synonyms of M. punctatum are not distinct from M. punctatum and treated here as members of M. punctatum. The six most important characters that separated eight species are stipe length, number of sori row between the adjacent secondary vein, sori diameter, sori density, primary-areole width, and spore width. These quantitative characters, together with some qualitative characters, were useful in constructing an identification key to these species. The differentiation between the studied taxa is discussed. According to RAPD data, M. punctatum cv. serratum and M. punctatum cv. grandiceps, were still recognized. The result of phylogenic study agreed with morphological and morphometric studies that separated M. glossophyllum and M. musifolium from M. punctatum. M. membranaceum and M. musifolium were basal most position of monophyletic clade of the complex. The larger clade was divided into four recognizable subclades.