Polypodium vulgare sens. lat. Polypody

The British polypody ferns (Polypodium spp.) form a group of 3 species, P. cambricum, P. interjectum and P. vulgare, which are sometimes lumped together as Polypodium vulgare sensu lato. They are not always easy to distinguish although typical specimens have some features that allow them to be assigned to a species in the field (see descriptions of individual species). However, accurate determination requires the observation of sporangial structures. These are described and illustrated clearly in Stace's New Flora of the British Isles. The main confusion concerns Common Polypody (Polypodium vulgare) and Intermediate Polypody (Polypodium interjectum). The sporangia of Common Polypody have 7-9 annulus cells with thickened walls, while those of Common Polypody (Polypodium vulgare) have 10-14 cells with thickened walls (see photos included with the descriptions of each species). However, hybridisation between each of these species gives rise to plants with intermediate characters which can present further problems. The hybrid between Intermediate Polypody and Common Polypody (Polypodium x mantoniae) is probably widespread in West Glamorgan but it is rarely recorded.