A Grimm’s Fairy Tale from Auld Reekie
Grimmia anodon Bruch & Schimper (Toothless Grimmia) in Holyrood Park, Edinburgh
Our tale begins 350,000,000 years ago along the Firth of Forth Geological Faults that are part of the major Southern Upland Fault. Tectonic activity spawned a series of volcanoes, the remnants of which dominate the Edinburgh landscape. The most prominent of these is Arthur’s Seat, an elemental 250 m sentinel that dominates Edinburgh’s skyline. So, if any of the four elementals is relevant to this offering, it must be Fire.
Grimmias are generally epilithic, growing in small grey-green, often hoary cushions on rock surfaces. The identification of the individual species can be quite challenging, especially when there are no capsules. Over the past 150 years eleven species of Grimmia have been recorded within the boundaries of the Holyrood Park; these have received considerable attention, partly due to the intellectual challenge that they engender and partly due to their accessibility, a few hundred metres from the Old Town of Edinburgh.
Grimmia anodon is a critically endangered member of the British bryoflora and has only ever definitely been recorded on a parapet of a bridge in Westmorland (last recorded in 1961 and possibly now extinct), and on crags on Arthur’s Seat in Edinburgh (NBN Atlas database). When in fruit it is comparatively easy to spot with a hand lens. This the only British species of Grimmia with sessile capsules that lack a peristome; without capsules it is just another Grimmia.
At this stage, a dynasty of naturalists connected with the Royal Botanic Garden, Edinburgh enters our tale. William Wilson Evans (1820-1886), an employee, deposited a specimen of Grimmia anodon from Arthur’s Seat in 1865 in the RBGE Herbarium. This interest in mosses was inherited by his son William Evans (1851-1922), who became the Herbarium Curator, and ultimately by his grandson William Edgar Evans (1882-1963). William Wilson Evans was an office bearer in the Botanical Society of Edinburgh and instigated dis-tribution of specimens from his collections. While this served as a laudable vehicle to distribute botanical material at a time when travel was difficult, there was the temptation to over-collect interesting species that might occur in small quantity in the wild.
Periodic references to the Grimmias on Arthur’s Seat were made in Botanical Society of Edinburgh’s publications up until a rather despondent contribution by McAndrew (1912). He suggested that several of these Grimmias, including G. anodon, had become extinct (see Table 1).
Could these extinctions be due to the reeking lumbs of the rapidly expanding population of Edinburgh? Our city suffers from sea fogs or haars, blown in by winds from the East. These haars used to hold air pollution from burning coal close to the ground and could have been the potential cause of extinction. On the other hand, it is not clear whether the exact locations of the Grimmias on Arthur’s Seat were common knowledge. While our sentinel looks like a uniform block of basalt, the geology is quite complex (Macadam & Clarkson, 1996).
Like all good fairy tales our story has a more or less happy ending. Periodically, bryophyte material from the Edinburgh Herbarium is sent away to international experts for confirmation of the determinations. Thus, a batch of Grimmia specimens was posted out around 2015; one of these, a specimen of the uncommon G. orbicularis (Round-fruited Grimmia), had been collected by David Long on Arthur’s Seat in October 1971. On its return, there was a note to the effect that the determination was correct, but that it was mixed with G. anodon. A subsequent visit to the site confirmed that it was still there. By the time of a further visit in 2018, the original G. anodon site was inaccessible due to encroachment by gorse, but it was found close by.
The probable original location of G. anodon had thus been identified, on agglomerate, a component of the complex geology associated with the Lion’s Haunch volcanic vent (Malcolm & Clarkson (eds.), 1996). A series of basalt columns crystallised out as the magma within the vent slowly cooled; these are known as Samson’s Ribs. This geology has been exposed during the glaciations, as south-west facing crags that would have taken the brunt of erosion caused by the movement of the ice sheets during the glaciations.
Two further uncommon species within the Grimmiaceae now enter our story. In 1940 a specimen of Coscinodon cribrosus (Sieve-tooth Moss) was collected on acid basalt on Arthur’s Seat by Ursula Duncan. This was confirmed in 2005, on basalt adjacent to Samson’s Ribs. During a survey to assess the status of this species in 2018, a population of Grimmia laevigata (Hoary Grimmia) was discovered just above Samson’s Ribs. As it happens, they also support several interesting native flowering plants, including Lychnis viscaria (Sticky Catchfly) and Dianthus deltoides (Maiden Pink), the fern Asplenium septentrionale (Forked Spleenwort), the liverwort Reboulia hemispherica and the lichen Lecanora andrewii.
Publications covering bryophytes within Britain can help us to assess why these crags are so special. Table 2 summarises ecological attributes extracted from the literature for a quartet of interesting epilithic species in the Family Grimmiaceae associated with this volcanic vent.
All four of these species are assigned to areas with low atmospheric nitrogen pollution. From Table 2 we can see that three of the four species are limited to low altitudes; both G. anodon and G. laevigata are categorised as thermophilous. Coscinodon is an exception as it is generally a species of acid rocks, including slate, especially on the west coasts of England in Wales, and has been recorded at 900 m; it is rare in Scotland. G. orbicularis is a species ofstrongly base-rich substrates. Thus, the complex geology of this volcanic vent is reflected in the attributes of this species assemblage.
Clearly, the ultramafic substrates associated with this volcanic vent are important (Macadam & Clarkson, 1996), but the aspect of the cliffs may be equally significant. On a sunny day, the dark rock surfaces are radiating heat, making them warm to the touch. This can raise the temperature of the air around the rock faces by as much as 10oC, creating a local micro-climate.
Sheep grazing, that had been a feature of Holyrood Park for at least 300 years (Mitchell, 2019) ceased in 1977. The unlikely suggested cause was a prank involving one of the sheep turning up in a room at the top of the adjacent student accommodation in Pollock Halls. However, I tend towards the view that contretemps between sheep and cars were becoming more common as the traffic flow through the Park increased. One consequence has been a very noticeable Gorse incursion. When in flower there is a spectacular display, accompanied a heady aroma from the nectar. However, there is a very significant increased fire risk. Ignition of the tinder dry detritus under the Gorse can be sparked by a single discarded glass bottle concentrating the sun’s rays, a discarded cigarette, or a lightning strike. Several years ago, there was a significant fire around Samson’s Ribs. More recently the blackened slopes around St. Anthony’s Chapel ruins are testament to another incident. Gorse incursion around the Lion’s Haunch increases the fire risk, right up to the rock faces.
Having dangled a botanical cornucopia from the Lion’s Haunch, I rush to submit a danger to life, do not enter notice. The encroachment by gorse makes the experience horrid, in the literal sense. Furthermore, the terrain around this volcanic vent is at best very steep and in places unstable, at worst precipitous with a risk of rock falls from the crags. The continuing well-being of Grimmia anodon poses a conservation dilemma that Yossarian, the lead character in the novel Catch 22 (Heller, 1961), would savour; it can be expressed thus. It would be mad not to control the gorse on the Lion’s Haunch. However, it is mad to contemplate the removal of the gorse that would cause soil erosion and expose the crucial crags to the weather, causing rock falls. The ultimate irony is that our Grimmia depends on rocks that were formed in the fiery entrails of a volcanic vent, and yet a gorse conflagration could be its nemesis.
Blockeel, T.L., Bosanquet, S.D.S, Hill, M.O. & Preston, C.D. (eds.). 2014. Atlas of British and Irish Bryophytes.
Heller, J. Catch 22. 1961. Simon & Schuster.
Hill, M.O, Preston, C.D., Bosanquet, S.D.S. & Roy, D.B. (2007, updated 2017). BRYOATT, Attributes of British and Irtish Mosses, Liverworts and Hornworts.
Macadam., A.D. & Clarkson, E.N.K. (eds.). 1996. Lothian Geology – An excursion guide.
McAndrew, J. 1912. Scottish Botanical Review, p. 205.
Mitchell, H. 2019. https://www.edinburghlive.co.uk/news/edinburgh-news/well-hilarious-reason-no-longer-15909116 (retrieved 5/3/2021).