Polypodies & Hard Ferns
What are they?
Ferns are primitive plants that evolved before the flowering plants and reproduce sexually by means of spores rather than seeds. This page covers the polypodies and hard ferns, species that have relatively small, narrow leaves and are once-pinnate, with the narrow side lobes of the leaves forming a ladder-like appearance.
Where are they found?
These are generally plants of shady places. Common Hard Fern is scarce in East Anglia as it favours damp, acidic soils that are more typical of northern and western Britain. The polypodies are common and widespread and may be found in coastal dunes, roadside hedgebanks and growing from walls. The precise distribution of the two species is currently unknown due to the difficulties of telling them apart, but more recent research has shown that Intermediate Polypody appears to be by far the commonest of the two in our region.
Identification
Common Hard Fern is a rich, dark green colour and is easily told by its distinctive leaves. The polypodies are a very difficult group of ferns to tell apart and it is necessary to use high magnification to examine ripe sori (spore cases) from the underside of the leaves to be able to safely tell the two species and their hybrid from one another. For ease of describing the various parts, a couple of technical terms are used; the side arms that form the first division of a leaf are called pinnae (singular, pinna), while the secondary divisions of the pinnae are called pinnules, which make up the smallest parts of each leaf.
Intermediate Polypody Polypodium interjectum
Native. Widespread and by far the commonest of the two species in East Anglia, being found on shady hedgebanks, ditch sides, shady churchyards and commonly on old walls, where it is more tolerant of limey mortar than is Common Polypody. Ripe spores present in late autumn or early winter. The leaf shape tends to be broadest about the middle and tapers toward each end and the pinnae are somewhat pointed at the tip. Under high magnification, the spore cases can be seen to consist of two halves, held together by a ribbed 'strap'. In Intermediate Polypody, this strap has on average 7-9 (extreme 4-13) ribs or bands, while Common Polypody has on average 10-14 (extreme 7-17) ribs.
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and ribbed straps |
Manton's Polypody Polypodium x mantoniae
Native. Probably under-recorded but could occur in shady places or on walls throughout much of the region. The leaf is rather variable in appearance and may often be rather uneven or distorted in overall shape, but they often resemble those of Intermediate Polypody in being widest about half way along the length of the leaf. Under high magnification, the spore cases can be seen to consist of two halves, held together by a ribbed 'strap'; this strap has on average 9-10 ribs or bands. Manton's Polypody is a hybrid between Common and Intermediate Polypody and is sterile, so no yellow or orange spores will be found and the sori will be seen to be empty when viewed under high magnification.
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and ribbed straps |
Common Polypody Polypodium vulgare
Native. Despite its name, this is by far the least common of the two species in East Anglia, being found most often on sandy, acidic soils and especially on coastal sand dunes. Ripe spores present in late autumn or early winter. The leaf shape tends to be more or less evenly wide throughout much of its length, tapering only toward each end and the pinnae are rather blunt at the tip. Under high magnification, the spore cases can be seen to consist of two halves, held together by a ribbed 'strap'. In Intermediate Polypody, this strap has on average 7-9 (extreme 4-13) ribs or bands, while Common Polypody has on average 10-14 (extreme 7-17) ribs.
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and ribbed straps |
Common Hard Fern Struthiopteris spicant
(Blechnum spicant) Native. A rather rare species in East Anglia, preferring a wetter climate and acidic soils, but it occurs at a handful of locations in East Suffolk and on the acid heaths of west and north-east Norfolk. Spore-bearing fronds may be found late summer onward. A small species, with leaves growing to 20-60cm in length. Leaves are of two types, all being just once-pinnate, without pinnules. The outer leaves are sterile and arch outward, while the inner leaves are narrower, fertile (bearing the spores) and stand upright in the centre of the plant.
Note: Most references will place this species in the genus Blechnum. The taxonomy here follows the specialist work of the Pteridophyte Phylogeny Group.
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