This distinctive and common evergreen fern brings a vivid green colour to the forest floor, particularly in winter.
Hard fern occurs throughout much of Europe, from Iceland, Britain and Ireland east to Latvia, Poland and Romania, and from Scandinavia south to Portugal, Spain, Sicily and Greece. Its range extends eastwards into Turkey, Georgia and Armenia, and it has also been recorded from Morocco, the Azores, Madeira and the Canary Islands.
A separate population exists along the northeastern edge of Asia, from the Kamchatka Peninsula in Russia to Japan. The species also occurs in western North America, where it is known by the common name of deer fern, and can be found from Alaska southwards through British Columbia, Washington and Idaho to Oregon and California.
Distribution in Scotland
Hard fern occurs throughout Scotland and can be found all over the mainland and the islands, including Orkney, Shetland, the Inner and Outer Hebrides and also on St. Kilda, the most remote and westerly part of the UK. It prefers acid soils and grows mainly in woodlands, occurring in both deciduous forests and the native pinewoods of the Caledonian Forest, as well as mature plantations of non-native conifers, where there is enough light for it to flourish.
Outside of woodlands, particularly in the wetter parts of the country, it also occurs in hedgerows, alongside watercourses and in moorland, where heather (Calluna vulgaris) provides a substitute for the shade of the forest canopy that it grows best under. Hard fern grows at a wide range of altitudes, and has been recorded from sea level to an elevation of over 1,000 metres on some of Scotland’s mountains.
Hard fern has not been assessed for its conservation status at an international level, so it does not feature on the IUCN Red List of Threatened Species. As a widespread and common species it is unlikely to be at risk, and is not considered to be of conservation concern.
Hard fern is an evergreen perennial fern in the family Polypodiaceae. It has shiny deep green straight fronds and, as with most ferns, these are pinnate, meaning that each frond consists of leaflets arranged on either side of the stem, opposite each other and tapering to a shorter length at both the tip and the bottom of the stem. Hard fern is singly pinnate, as each frond has only one series of leaflets on it, whereas many ferns are bi-pinnate, with each leaflet subdivided again into further leaflets, and bracken (Pteridium aquilinum) is tri-pinnate, with each leaflet subdividing three times. This singly pinnate feature of hard fern gives its fronds their linear appearance, whereas most other ferns in the UK have fronds that are more triangular in shape, because of their more complex pinnation.
Hard fern is also distinctive because it has two different types of fronds, both of which emerge from the centre of the fern, in a rosette-like pattern. One type consists of the sterile fronds, which generally lie flat on the ground and are up to 30 cm. long. Their main function is to harness the sun’s energy through photosynthesis, so that the fern can grow. In the middle of the sterile fronds, the fertile fronds grow more upright in a central cluster, reaching a height of up to 50 cm. These are narrower than the sterile fronds, with their leaflets spaced further apart from each other, and the edges of the leaflets are usually rolled down towards their undersides.
As their name suggests, the role of the fertile fronds is for propagation, and the underside of each one is covered with the fern’s reproductive structures. These are called sori, and are linear in shape and brown in colour. Each of the sori consists of a mass of sporangia, which produce the fern’s spores. The sporangia mature during the summer and then burst open, releasing their microscopically-sized spores, which drift away on air currents and winds.
Like all ferns, hard fern has a two stage reproductive cycle that differentiates it from flowering plants and conifers. A spore that lands in suitable conditions grows into a tiny heart-shaped plant, less than 1 cm. in size, called a prothallus or gametophyte, which looks nothing like the adult fern. This has only half the genetic material of the mature fern, and is an intermediate stage of development between the spore and the adult fern. The gametophyte has two sets of reproductive organs on its underside, and in moist conditions sperm cells swim from the male organs to the egg cells of the female organs on either the same gametophyte or another one nearby. When a sperm cell meets an egg cell, they fuse together, creating a cell with a full set of adult fern genes. This then grows on to become the sporophyte – the adult hard fern that is familiar to us – over a period of two to four years.
The sterile and fertile fronds grow out from the fern’s rhizomes, which are a specially-adapted type of root that enables hard fern to spread vegetatively, forming small clumps. After releasing their spores, the fertile fronds die back each autumn, but the sterile fronds can persist for several years, gradually dying off and being replaced by newer ones. Little data is available on the actual lifespan of an individual hard fern plant, but they are thought to live for many years.
Like many ferns, hard fern has relatively few ecological relationships with other organisms, compared to the other vascular plants (ie not ferns) that make up the majority of the plant kingdom. For example, in Britain there are no species of moths whose caterpillars feed specifically on hard fern, although the larvae of a few polyphagous moths (those that feed on many different plant species), such as the broom moth (Ceramica pisi), will occasionally eat the fronds. In mainland Europe, the newly-emerged larvae of the green angle shades moth (Phlogophora sticta) have been recorded feeding on hard fern, but that moth does not occur in the UK.
There are two species of invertebrates whose larvae make mines in hard fern. One of these is a fly (Chirosia histricina), the larvae of which live in the leaflets of the fronds, while the other is a sawfly (Heptamelus ochroleucus), whose larvae make mines in the frond’s stem or petiole. A previously unknown species of nematode (Ditylenchus sp.) has recently been found as a parasite in the leaves and stems of hard ferns growing at a high elevation in the Alps in Germany.
A number of microfungi are associated with hard fern, the most common of which is hard fern rust (Milesina blechni). This induces small galls to appear on the underside of the fronds, and causes a discolouration of the fronds themselves. Another fungus (Cephaloscypha mairei) occurs on dead fronds and stems, helping to break them down and return the nutrients they contain back to the soil.
Hard fern is eaten by red deer (Cervus elaphus), particularly in winter, when it is often one of the few remaining green plants available to them. In western North America, this palatability to elk (as red deer are known there) and other deer has given rise to the species’ common name of deer fern. Indeed, in some places the fern is grown deliberately as a fodder crop for deer and elk. It is also browsed by moose (Alces alces) in North America, and it is likely have been eaten by that species in Scotland as well, before its extinction here. In the past, the indigenous people in western North America ate the fern’s rhizomes, although usually only as an emergency food, and used the fronds to treat skin ailments. This latter use is believed to have been derived from observations by native people of deer that had recently lost their antlers rubbing their antler stubs on deer fern fronds to help them heal – this is another possible source of the common name for the fern there.
Alan Watson Featherstone
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