Duncan Mcewan / Common polypody fern (Polypodium vulgare) Sori on underside of frond, Scotland

Duncan Mcewan / Common polypody fern (Polypodium vulgare) sori on underside of frond, Scotland

Alan Watson / Unfurling frond of Common Polypody fern (Polypodium vulgare) on an Oak tree (Quercus petraea) in temperate forest, Killarney National Park, County Kerry, Republic of Ireland, Europe

Alan Watson / Polypody ferns (Polypodium vulgare) and Moss on the trunk of Oak tree (Quercus petraea) Tomies Wood, Killarney National Park, County Kerry, Republic of Ireland, Europe

Jerry Monkman / Common polypody fern / fiddlehead {Polypodium vulgare} frond unfurling, Boxford, Massachusetts, USA

Jerry Monkman / Common polypody fern / fiddlehead {Polypodium vulgare} frond unfurling, Boxford, Massachusetts, USA

Duncan Mcewan / Polypody fern on fallen tree {Polypodium vulgare}, Oakwood, Inverness-shire, Scotland

Philippe Clement / Frond of Common polypody fern {Polypodium vulgare} showing spores on underside, Belgium

Philippe Clement / Common polypody fern {Polypodium vulgare} in woodland, Belgium

Philippe Clement / Frond of Common polypody fern {Polypodium vulgare} showing spores on underside, Belgium

Philippe Clement / Common polypody {Polypodium vulgare}close-up of frond, La Brenne, France.

Duncan Mcewan / Frosted polypody fern & sphagnum {Polypodium vulgare}, Oakwood, nr Inverness, Scotland

Niall Benvie / Common polypody fern {Polypodium vulgare} and moss, Slitere NP, Latvia

Duncan Mcewan / Common polypody fern (Polypodium vulgare) on oak branch. Scotland, UK, Europe