Morphology and micromorphology: A new look at the intraspecific variation of the Fontinalis antipyretica complex and its taxonomic implications

The taxonomy of the Fontinalis antipyretica complex has long been a subject of debate, with recent molecular studies often suggesting a broad, polymorphic species concept. This study challenges the current consensus by a multidimensional morphometric analysis of the gametophytic and sporophytic micromorphology, supported by the examination of 44 type specimens, and allows a revision of the Fontinalis antipyretica complex. Hierarchical Cluster Analysis (HCA) and Principal Component Analysis (PCA) demonstrated full congruence, distinguishing nine groups that differ in the range of variation across all analyzed traits: leaf dimensions and leaf cell parameters of their gametophyte. The dendrogram structure revealed a division of specimens into two main groups: those with longer and wider leaves and cells, and specimens with shorter and narrower leaves and leaf cells. Consequently, considering the obtained results and the marked distinctiveness of each analyzed group, the research beyond Fontinalis antipyretica sensu stricto, allowed for the reinstatement to species rank of F. androgyna R.Ruthe, F. bryhnii Limpr., F. cavifolia Warnst. & M. Fleisch., F. gracilis Lindb., F. kindbergii Renauld & Cardot, and F. minor Brid. Furthermore, it enabled the proposal of new combinations—F. cymbifolia (W.E.Nicholson) Wolski comb. nov., and the description of F. larssonii Wolski sp. nov. A crucial complement to the morphometrics proved to be the micromorphology of the sporophytic exostome of the studied specimens. Substantial differences were demonstrated in the ornamentation of the tooth surfaces—ranging from nearly smooth in F. larssonii, through baculate papillae in F. antipyretica, to angular tubercles in F. cymbifolia. The results prove that within the analyzed taxa, cellular parameters combined with peristome ultrastructure provide a stable basis for the discrimination of the studied specimens. Thus, the conducted research not only systematizes our knowledge of the Fontinalis antipyretica complex and enriches it with previously unpublished micromorphological data but also provides an intelligible identification key for the described taxa, offering a practical tool for analyzing the intraspecific variation of Fontinalis antipyretica sensu lato.