In early January I spent a day out in Glen Cannich, and during the morning my attention was focused on the wonderful atmospheric conditions created by the mist drifting along the hillsides and over the old Scots pines (Pinus sylvestris) there. I also photographed some red deer (Cervus elaphus). By lunch time however, the mist was gone and the deer had moved away so in the afternoon I began exploring the rocky knolls in the area below the Mullardoch dam. There are no trees there at all, so I don’t usually spend any time in that spot, because it’s rather bleak and desolate.
However, this day, perhaps due to the damp, overcast conditions, I noticed how many lichens there were on some of the rocks. Because lichens are dependent on atmospheric moisture for their water, they become desiccated and shrivelled on dry days, but when it is wet, they swell up to their full size and positively exude vibrancy and vigour. There were a few individual rocks scattered through the area, but it was the larger clusters that attracted me, because of the denser concentration of lichens they contained.
At a casual glance there may not appear to be much of interest on a bunch of rocks like this, but in fact in many cases there’s very little of the mineral structure of the rocks visible at all. This is because the entirety of the exposed surfaces of the rocks are covered in crustose lichens. These are the lichens that grow flush with their substrate – in this case the rocks.
Some of these lichens are brightly-coloured, particularly in various shades of orange and yellow, and when they grow together they make a beautiful mosaic-like patchwork on the surface of a rock.
Crustose lichens are at the front line of the interface between the mineral kingdom and organic life-forms. This is due to their conversion of minerals into organic substances that can be utilised by a range of life forms, particularly plants. By growing on rocks, they cause weathering of the mineral surface by two different mechanisms. One is by the alternate swelling and contraction of the lichen thallus (as the main body of a lichen is known) in tiny crevices in the rock surface, due to periods of wet and dry weather. This can cause small scale fracturing of the rock surface, freeing up tiny mineral particles. The other mechanism is a chemical one. Some crustose lichens secrete acids, particularly oxalic acid, that dissolve the minerals of the rock itself and bind them to organic molecules in a process called chelation. The resultant mineral complexes are an essential component in the formation of soil, which provides the nutrients for most plants.
There are numerous different crustose lichens and some of them are hard to identify, as there are many species that are very similar to each other. However, some of them are more straightforward, and one of the most distinctive and easy to identify is the blood spot lichen (Ophioparma ventosa). This has a pale, slightly greenish-coloured thallus, and dark red apothecia that resemble small spots of blood.
One of the easiest crustose lichens to identify is map lichen (Rhizocarpon geographicum). It’s a very common species, and this is indicated by the fact that it is one of the relatively few lichens with a common name. It is bright green in colour, with a black perimeter, and it grows in patches that are said to resemble maps, hence its English name.
Map lichen is very widely distributed, occurring at northern latitudes in North America, the UK, Scandinavia and Asia, as well as in Patagonia and the Antarctic Peninsula. On another nearby rock, there were two different whitish lichens growing next to each other, and one of those had blackish raised lumps on its thallus. These were not the apothecia – the part that releases the spores of the fungal partner in the symbiotic organism that is a lichen – but instead were a lichenicolous fungus (Sclerococcum sphaerale) growing as a parasite on the lichen (Pertusaria corallina).
This white lichen was visible on quite a few of the rocks, and on one it was growing right next to a band of white quartz. Quartz veins are fairly common in the rocks in the Highlands of Scotland, many of which are schists. These are metamorphic rocks, meaning that they have been changed in form from their original composition due to the effects of heat and pressure inside the Earth’s crust. The quartz veins are thought to originate from the process of crystallisation, when minerals dissolved in an aqueous solution precipitate out while the surrounding rocks are still in a molten condition.
Some of the rocks just had small patches of quartz in them, whilst others had larger, multiple veins running through them.
Whenever I see quartz veins like this, they always act as a potent reminder for me of both the immense geological forces that have helped to shape the world as we know it today, and also the vast stretches of time that rocks like this have been in existence on the planet, slowly getting worn down and eroded by glaciers, water and lichens. There is a sense of timelessness about these rock formations that provides an almost overwhelming contrast with the comparative brevity of our human lifespans.
The combination of rocks with lichens growing on them also reminds me of the privilege it is to live at this time, after the actions of lichens and glaciers etc have done their work of breaking up the rocks over millions of years, enabling organic life to flourish. That in turn has led to the remarkable diversity of life on the planet today. All of that is ultimately due to the presence of mineral nutrients in the soil, that plants use for their growth. When the plants are eaten by animals (and people) those same mineral-derived nutrients then are incorporated into their bodies …
Some of these rocks also had foliose, or ‘leaf-like’ lichens growing on them. These do not grow flush on the rocks, but instead have a three dimensional structure to them, with some of the thallus at least growing away from the mineral surface. One of the commonest of these lichens in Scotland is the one known as crottle, or alternatively, salted shield lichen (Parmelia saxatlis). It is greenish-grey or blueish-grey in colour, and has traditionally been used as a source of dyes, for example in Harris tweed.
While it mostly occurs on rocks, crottle is also occasionally found growing on trees that have acid bark, such as birches. It’s one of the lichens which has a distinctive growth pattern, radiating outwards from a central point where it must have first become established. This often produces irregular, somewhat circular shapes, and adjacent patches will merge together. Brown apothecia are occasionally found on this species, but most of the time I don’t see them, so their occurrence is relatively unusual, at least in my experience.
Interestingly enough, there were quite a few patches of the crottle lichen on the rocks on this day that did have apothecia on them. I don’t know the reason for this – was it the time of year that made the conditions more suitable for the dispersal of the spores of the lichen’s fungal partner? Or is it just the case that the crottle lichens in this area have a greater propensity to produce apothecia? There’s always so much more to learn in Nature …
On one of the rocks with extensive patches of crottle lichen, some bright red flashes of colour caught my eye. These were the apothecia on the cup-like structures, or podetia, of one of the Cladonia lichens (Cladonia coccifera agg.).
There are several different species of Cladonia lichens that produce these ‘pixie cup’ structures and lichenologists are still working to identify the actual species in some cases. As an interim measure, ones like these here are aggregated together under the single name Cladonia coccifera agg., until the differences between them can be clarified. To my eyes, these are some of the most beautiful and interesting of all lichens, and the podetia are all unique in their shapes, and different to one another, with varied sizes and groupings of the red apothecia on the rim of the cups.
On another rock, just a few metres away, I found some more of the same Cladonia coccifera agg. lichen, this time growing amongst a close relative of the crottle lichen – Parmelia omphalodes. This is more brownish in colour, but has a similar growth pattern of its thallus to the crottle lichen, and indeed there were some small patches of the latter in amongst it. The bright red apothecia of the Cladonia really stood out in contrast to the brown lichen all around it. Once again too, none of the rock surface itself was visible, as the lichens had covered that entirely.
The red apothecia seemed to almost glow with an inner radiance or light, appearing vibrant and intensely alive with their brilliant colour …
As I continued looking at the rocks, I found more and more different lichens growing on them, in just a relatively small area. On one there was what looked like quite a distinctive brown lichen, which I thought might be easy to identify. However, when I sent the photo to John Douglass, the lichenologist who helps me with identifications, he replied that he could only say that it was a species of Umbilicaria. There are a number of species in this genus that occur throughout the northern regions of the world. They are commonly known as rock tripe, and several of them are edible.
On a different rock, there was another slightly different looking lichen which John was able to identify to species level – it was Umbilicaria polyrrhiza. As far as I can tell, it’s not one of the edible species though. Growing as it was, beside some map lichen (Rhizocarpon geographicum), a white Stereocaulon sp. lichen and some brownish moss, it formed part of another multi-coloured tableau of lichen beauty and diversity – a miniature world that provided great visual and aesthetic delight for me.
Although I hadn’t intended to at all, I ended up spending the rest of the day with these lichen-covered rocks. However, because it was early January, the light faded early and before 4 pm it was too dark to take photographs, so it was a short day overall. It had two distinct halves to it, which is one of the reasons for making two separate blogs from the day. Later, I also realised that, without me having been aware of it at the time, this second part of the blog continued a theme that has developed in my recent blogs from Glen Cannich, of a focus on lichens in them. Looking back through some of the other recent blog articles I’ve written from this glen, one in 2015 and another in 2014 both had a strong emphasis on lichens in them. There’s two reasons for this I think. The first is that there are indeed a variety of rocks in the glen that are both quite visible and have good lichen colonies growing on them. The second is that in some parts of the glen at least, such as the area I spent this afternoon in, there are very few, if any, trees, and the deforested landscape is quite barren, meaning that the rocks, and the lichens they support, are some of the few features of interest there. However, this also goes to show that, even in what seemed like an area with little to offer in terms of biological diversity, there is in fact a whole world to explore, just on a small and localised scale.
My thanks to John Douglass for his help in identifying many of the lichen species featured in this blog.