Ferns
Ferns
Not all ferns stay green all year, and you’ll see new fronds unfurling in the spring. Credit Ben Andrew (rspb-images.com)
The humidity of Scotland’s rainforest make it a perfect place for ferns. They festoon the woodland floor, but you’ll also find them growing out of trees and rocks, often relying on clumps of moss for moisture. So remember to look up when you’re exploring, as you could well see ferns growing above your head!
The rainforest has ferns of lots of different shapes and sizes, from tiny filmy ferns up to huge ferns almost 2m tall. Some die back in the winter, and you’ll spot their fresh fronds unfurling in the spring. Others are hardier and stay green all year.
Ferns are similar to mosses and liverworts in that they don’t flower, but they’re different because they have proper leaves and roots. There are around 60 species in the UK, and you’ll find lots of them in Scotland’s rainforest, but, they can be very tricky to tell apart. If you want to give it a go, you’ll need time, patience and a good ID guide. This page from The Woodland Trust, will get you started https://www.woodlandtrust.org.uk/trees-woods-and-wildlife/plants/ferns/.
There are a few species of fern that become more common in the ‘rainforest zone’, and when they’re abundant they can act as indicator species. Here are two to look out for:
Hay-scented buckler fern
It doesn’t smell of hay, so there’s no point sniffing it! Credit Gus Routledge
Despite their name, these ferns don’t smell of hay when they’re green. The dried fronds do, but that’s true of all ferns, so sniffing them won’t help with identification!
Like many ferns, these like the shade, but they also stay green all winter, which is unique for buckler ferns. If you look closely, you may also spot that they appear crinkled, because the edges of the individual ‘leaflets’ (called pinnules) are up-turned.
Wilson’s filmy fern
These tiny ferns are often mistaken for moss. Credit Lorne Gill, WTML
Filmy ferns are a distinct fern ‘family’ and there are around 600 species globally. They’re mostly found in tropical rainforests, but a small number of species can survive in cooler, temperate rainforests.
They’re very different to the ferns you may be familiar with from most UK woodlands, if for no other reason than because they’re tiny. In fact, they’re easily mistaken for a moss or liverwort.
Two species of filmy ferns grow in Scotland’s rainforest, and Wilson's filmy fern is the most widespread. It's named for botanist William Wilson who studied the ferns in the early 19th century. He distinguished two separate species, the second being the less-common Tunbridge filmy fern.
Wilson’s filmy fern is usually found in small colonies growing on trees, often near the ground, though it can form colonies on rock faces. It’s often found growing mixed up with lots of bryophytes and lichens.
Tunbridge filmy fern
Named for the first place it was found in the UK (Tunbridge Wells in 1686) Tunbridge filmy ferns are less tolerant of drying out than Wilson’s, and so tend to be found in shadier, more sheltered locations. They can form quite large colonies, usually on rock faces, and while slow growing, if left undisturbed it’s thought the colonies could last for hundreds of years.
The two filmy ferns are quite tricky to tell apart, but if you want to give it a go, your best bet is to use a hand lens to get a close-up view (or you could take a picture on your phone and zoom in).
Wilson's filmy fern is smaller and more delicate than Tunbridge filmy fern, which can be a bit more blue, though not always. In Wilson’s, the leaflets are thinner and more see-through, and the veins generally go all the way to the ends of the leaflets, while in Tunbridge they tend to stop just short of the ends.
A good feature to look out for is the sori, which are clusters of sporangia, the ball-like structures that produce and contain spores. These are protected by a flap of tissue called indusium, and the edges of these in Tunbridge are jagged (which you can see in the photo above) while in Wilson’s, they’re smooth.
Tunbridge filmy fern. Credit Jenny Tweedie
Polypody fern
Polypody ferns are a classic feature of Scotland’s rainforest. They’re often seen growing on tree trunks or branches, sometimes in great numbers, but can also grow on rocks, banks and on the forest floor where there is steady moisture and soft sunlight. Their tough leaves often stay year-round, helping to keep the woods green even in winter.
Polypody ferns on a tree branch. Credit John MacPherson
