Reviewing the identity of the Maltese Polypodium (Polypodiaceae) – new evidence from morphology and flow cytometry

The first record of Polypodium from Gozo (Maltese Islands) was described as a new endemic taxon, Polypodium vulgare subsp. melitense, based on its unique set of morphological characters. It was treated as a novelty and designated as a subspecies of P. vulgare mainly due to the lack of paraphyses, the presence of 10–16 annular cells, and a mean spore length of 64 μm. The fern was reassessed by us employing a more rigid morphological analysis and the application of flow cytometry. The absence of paraphyses was confirmed, but the number of annular cells (5–11) and the spore length (70–79 μm) differed from the previous study. These and other morphological traits, the phenology (leaf-shedding in spring), the calcareous growth habitat, and the southern distribution implied that the fern is P. cambricum. Final confirmation was obtained from flow cytometry; the genome size of 17 pg corresponds perfectly with the range obtained for other accessions of this diploid species. The Polypodium reported from Malta does not merit taxonomic distinction despite being a rare form of P. cambricum, which lacks paraphyses.