Alan Watson Featherstone, the founder of Trees for Life, writes about his experiences out in the Caledonian Forest, and about his work for the charity.

A great day for lichens

Lichen-covered birch trees in Glen Affric.

The weather forecast on Saturday was for high winds and rain, but I decided to go out for the day anyway, thinking that the conditions might make for some interesting photographs. Following my intuition, I went to Glen Affric and stopped at an area downstream of the dam in the glen, at a point where I knew there were lots of lichens on the trees. I’d been intending to go there for a while, so it seemed like an ideal day to do so.

Birch trunks covered in beard lichen (Usnea filipendula) and other lichens.

With the trees’ leaves gone, I knew the lichens would be much more visible, and in the wet conditions they would be fully expanded and vibrant (they dry up and shrivel in dry weather). In addition, because the ground slopes away down from the road, many of the lichen-laden branches of the trees are at eye level, providing an ideal opportunity to observe and photograph them.

Close up of the lichens festooning the branches of one of the trees.

When I arrived at that area of the glen, the lichens were indeed spectacular in their abundance and visibility on the trees. Beard lichens (Usnea filipendula) were the most prominent, with their long trailing strands hanging down 20 cm. or more from some of the branches and trunks. They made for a duotone-coloured landscape, with their pale yellow colouration contrasting with the silvery-grey of the birch trunks and the other lichens growing on them. Somehow, this combination seemed like a faint reminder or echo of the brighter colours of the trees just a month ago, when the birch leaves were brilliant yellow.

Dog Lichen (Peltigera membranacea) growing on a rock, showing its typical lobed shape and colouration.

Another view of the dog lichen (Peltigera membranacea). The light-reddish brown parts are the apothecia, which release the spores from the fungal symbiont in the lichen.

As I looked at the birches, my attention was drawn to a large rock beside the road, at the base of one of the birches that had an eared willow (Salix aurita) growing beside it. What had caught my eye was a large, spreading patch of a dog lichen, covering much of the top of the boulder. Dog lichens are amongst the largest lichens in Scotland and are foliose, or leaf-like, in their growth. This was one of the commoner species (Peltigera membranacea), which has dark greenish-black lobes, often with pale reddish-brown discs rising up from their edges. These are the apothecia, the structures that release the spores from the fungal partner in the lichen symbiosis.

Detail of the lichen's lobes, showing the rhizines, and the undersides of the apothecia - note the pattern of veins there.

This patch was particularly vibrant and colourful, probably due to the moist conditions, and had abundant apothecia. Their colour, and that of the upper surfaces of the lichen’s lobes, contrasted dramatically with the pale, near-white colour of the undersides, which were covered with sharply pointed, downward-facing spines. These are called rhizines and are root-like structures that absorb nutrients and, in some cases, help to anchor the lichen to its substrate (ie the rock in this instance). This species of dog lichen has some of the most spectacular rhizines of all, forming a dense concentration of spikes on the underside of the thallus, as the main part of the lichen body is known.

Close up shot, showing more detail of the apothecia, and the veins and rhizines on the underside of the lichen thallus.

This was the best example of this species of dog lichen that I’ve yet come across, and I spent quite a while with it, as it was visually so interesting. Also, because it was growing on top of a rock, this patch of lichen could be observed very close up without having to lie down on the ground! The lobes with their apothecia, rhizines and raised veins made for a fantastic and intricate miniature landscape – another of Nature’s wonderfully creative and living works of art.

Another close up shot of the rhizines and the veins on the underside of the lichen's thallus.

Like all lichens, this species is a symbiosis between a fungus (the mycobiont) and a photobiont (the partner that is able to photosynthesise – ie gain energy from the sun – which fungi are unable to do). Whereas in most lichens the photobiont is an alga, in this dog lichen it is a cyanobacterium (Nostoc sp.). This symbiotic partnership has made lichens one of the most successful groups of organisms in the world, colonising virtually every terrestrial habitat, from mountain tops and deserts to tropical rainforests and even Antarctica, where lichens are some of the very few terrestrial organisms that are able to grow.

Lichen on fallen twig amongst common haircap moss (Polytrichum commune).

Eventually, after taking over 50 photographs of the dog lichen, I moved on down the slope, and my eye was drawn by some fallen lichen that was lying amongst a patch of common haircap moss (Polytrichum commune). The individual stems of this moss species always remind me of miniature young pine seedlings, when viewed from above, and I like the pattern they make when growing closely together like this.

Willow jelly fungi (Exidia recisa) on the twig of an eared willow (Salix aurita).

Clambering carefully over the mossy rocks on the slope, I passed by another eared willow and noticed some unusual shapes on a few of its twigs. Stopping to have a closer look, I saw that they were the fruiting bodies of a jelly fungus, similar to some (Exidia repanda) I have seen before on birch twigs in Glen Affric. Subsequent correspondence with Liz Holden (mycologist) has confirmed that they are a closely-related species, willow jelly (Exidia recisa), that occurs on willows, whereas the other one is confined to birches.

Another cluster of the willow jelly fungi (Exidia recisa).

These jelly fungi fruit mainly in the winter, and have been under-recorded in Scotland, so there are not many records of them. In fact this sighting I made is one of the first in the area to the west of the Great Glen in the Highlands. On dry days the fruit bodies are all shrivelled up and quite inconspicuous, so it’s best to look for them on wet days, when they are fully hydrated and live up to their name as being jelly fungi – they are just like blobs of jelly stuck on to the twigs of willow bushes!



5 Responses to A great day for lichens

  1. Sandie Howison says:

    Hi Alan
    Was hoping to order two of your Desk Diaries but see you haven’t produced them this year – Kendra and Roger will be so disappointed, having used them for quite a number of years now.
    The plus side is that I have come across your blog and found it really interesting.
    Hope all is well with you and Kevin.
    Love and Best Wishes
    Cousin Sandie

  2. Rick Jaspers says:

    Hi Alan, through this post I was able to identify the jelly that I found growing in my backyard. I also used this article as a source for the information on a blog of my own. I thought you might be interested. If so, go to:
    Thanks so much for writing such a fascinating article. Best wishes for all your discoveries in the forest.

    • alan says:

      Hi Rick, thanks for your comment, and I’m very pleased that my blog enabled you to identify the same fungus that you’d photographed – that’s great. I had a look at your blog, and you have some nice photos there too – thanks for putting a link to my blog in it! With best wishes, Alan

  3. Rick Jaspers says:

    Hi Alan, this is the second time this particular post has been helpful in assisting me with an identification. The other day I found some lichens which I recalled seeing somewhere before. On a hunch, I came back to this site. The dog lichens I found were not the same species as the ones you have pictured, but knowing the genus was extremely helpful. After some further research, I decided that I could not make a precise identification by visual inspection alone. I have quickly come to the conclusion that lichen taxonomy can be an insurmountable challenge for the non-professional.

    • alan says:

      Hi Rick, I’m glad my blog is continuing to be helpful to you! Some of the dog lichens are relatively easy to identify for an amateur like me, but others can be a challenge, even for a professional. We have two green species here in the Highlands, Peltigera britannica and Peltigera leucophlebia, which even the lichenologist I use for identifications has to consult with a greater expert than himself, to tell them apart! You have a lot of beautiful dog lichens in the Pacific Northwest – I’m most familiar with them in the temperate rainforests of British Columbia.

      By the way, I photographed some more of the willow jelly fungi (Exidia recisa) last week-end and will be adding a new blog including some images of them in the next day or so.

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