I love ferns. In shady, moist conditions it’s possible to grow many varieties. But where the soil is drier, it’s still possible to grow one species of fern, the Common Polypody, Polypodium vulgare.
The Common Polypody is a tough and resilient perennial and, once established, it thrives in dry conditions. In the wild it grows in the forks of tree branches and on top of dry banks and drystone walls. In very dry weather the fern will roll up its leaves to conserve water, but rain will cause the leaves to unfurl again. It is an evergreen plant, so it provides lovely greenery throughout the year. We planted it beneath Birch and Italian Alder trees at the Belvedere Centre in Norwich, where it has established well.
For gardeners, Polypodium vulgare is a very useful plant. Several varieties can be grown, as well as the related Licorice Fern, Polypodium glycyrrhiza ‘Longicaudatum’.
In the wild, the Common Polypody can be found almost throughout Britain (see map). It is easy to tell that it’s a Polypody, but less easy to pin it down to species. There are actually three species of Polypodium in the British Isles: Polypodium vulgare, P. interjectum and P. cambricum, as well as hybrids between the species.
In Norfolk, we have P. vulgare, P. interjectum and P. x mantoniae (a hybrid between P. vulgare and P. interjectum). P. vulgare tends to grow in more acidic conditions than P. interjectum, which likes slightly alkaline growing conditions, whether from the mortar on walls or from salt-bearing seaside winds. Polypodium cambricum perfers milder winters and has a more south-westerly distribution in the British Isles.
You need to look closely at the ferns to make an identification. Although leaf shape can be a useful guide, the real test relies on the structure of the sporangium (plural sporangia), the structure that encloses the spores and, when they are ripe, catapults them away from the parent plant. (See also http://blogs.scientificamerican.com/artful-amoeba/wonderful-things-ferns-eject-their-spores-with-medieval-style-catapults/.) There are some good photos of Polypodys on the Nature Spot website, and more information on the Fern Id and Ferns In Britain and Ireland websites.
The Plants for a Future website reports that the root can be eaten and has a “unique, rather unpleasant odour and a sweet (cloying) flavour at first though it quickly becomes nauseating”. The plant also has several possible medicinal uses.
Polypody ferns, Polypodium sp., growing on the North Norfolk coast
Updated 18th January 2016 with details of other Polypodium species found in the British Isles.
