Lichen growth is a perennial but rarely remarked feature of a megaltihic site visit. Mark Greener explains why we should take notice
Lichens are easy to overlook: seemingly nondescript splodges on megaliths, insignificant against the scale of the stone let alone compared with the grandeur of the sacred landscape. Yet they’re integral to megalithic beauty: a lichen-free megalith seems, to me at least, incomplete, unfinished, almost anachronistic. After all, lichens are famously long-lived: some species may see their 10,000th birthday.1 And over the centuries, lichen communities help shape megaliths. Perhaps, lichens even once formed a canvas for Neolithic, Chalcolithic and Bronze age art.
As a biologist, lichens are fascinating. They form from a filamentous fungus (the mycobiont) and at least one microscopic alga or cyanobacterium capable of photosynthesis (the photobiont). The relationship is so close that a lichen seems to be a single organism.2 It’s a highly successful strategy: more than 13,500 fungal species and approximately 100 photobiont species can form lichens. Indeed, almost a fifth of all fungal species survive only by forming lichens.2
The huge number of possible combinations of fungi and photobionts allows lichens to colonise almost every ecological niche, including the surface of (epilithic) or inside rocks (endolithic).2 As they grow, lichens change their environment. For example, acids produced by some lichens may help erode megaliths. Other lichens seem to help protect the underlying stones from the environment.3
Lichen at Duddo 5 Stones
Lichen diversity and human activity
Human activity also influences lichen communities on megaliths. Historically, megaliths in the Netherlands resided in open heathland. Today, many Dutch megaliths are at least partly shaded by trees and shrubs, which can influence the lichen communities on the stone.4 Movement and re-erection may alter lichen communities on a particular megalith.3 The clan warfare in the late 1700s and early 1800s that toppled some of Easter Island’s moai probably altered the lichen, for example.1 Dressing stone (and even archaeological investigations) can change existing species, while quarrying can expose previously lichen-free surfaces (as we’ll see this can help date the site).1 In other words, the relationship between the megalith and the lichens is dynamic.
So, assessing changes in lichen communities on megaliths is difficult. To complicate matters further, lichenologists recognise an increasing number of species and are improving their ability to differentiate samples that look similar. In addition, some lichens are exquisitely sensitive to air pollution,2 which has, obviously changed over time. (As an aside: other lichens are remarkably resilient. Nearly 70-100% of specimens of the ‘Map Lichen’ Rhizocarpon geographicum and the ‘Elegant Sunburst Lichen’ Xanthoria elegans germinated and grew after being launched into Earth orbit and exposed to space for between 11 and 14 days.5)
Lichens’ ability to colonise specific niches means several species can occupy the same megalith. A study of a reclining figure sculpted by Henry Moore found nitrogen-loving lichens colonising the head and knee. These areas are popular as bird perches and guano is rich in nitrogen. The statues’ armpit was, aptly, moist. Several moisture-living species colonised the armpit. The back hosted another lichen community; this time those that preferred dry, shaded areas.6
This predilection for a particular niche helps explain the remarkable lichen diversity on megaliths. In 2000, researchers identified 128 species of lichen on 54 megalithic graves built by the Funnel Beaker culture 3500–2700 BCE in the Netherlands. On average, each dolmen had 28 species of lichen. But one megalith harboured 56 species.4 A study published in 2016 found 75 species of lichen on the Rollright stones in Oxfordshire.3
Native American lichenoglyphs
Which brings us to lichens as a canvas for rock art: Native Americans in NW Ontario, Canada, created images by scraping lichens from rock faces. Because lichens grow slowly and at relatively constant rates, these ‘lichenoglyphs’ can last for centuries.6 Indeed, some lichens act as biological chronometers helping scientists to date, for example, the Easter Island megaliths (a technique called lichenometry).1,6 A study reported in 1988 suggested that some specimens of a chalky white lichen called Aspicilia calcarea on the Rollright stones may be more than 800 years old.3
But that’s almost infantile compared with a 280mm specimen of R. geographicum on Baffin Island in Canada, dated at 9500 years old, or the 370 mm Rhizocarpon discovered in the Brooks mountain range in N Alaska, which is estimated at 10000-11500 years old.1 These are not isolated examples and, relatively commonly, Rhizocarpon may live for 4000-5000 years.1
Time, nevertheless, will have taken its toll and most lichenoglyphs will probably have degraded. I wouldn’t draw too many conclusions from a single example, but Indian Rock Paintings of the Great Lakes hints that lichenoglyphs might have once been common. Of 16 images in the narrows of Obabikon Lake, Ontario, in the early 1960s, 13 were rock paintings, two petroglyphs (cut into the rock) and one lichenoglyph.7
The Canadian lichenoglyphs have several themes. One Ontarian lichenoglyph, on a boulder, shows a “devil-face”.7 There’s also an impressive Thunderbird lichenoglyph on rock at Reindeer Lake, Saskatchewan (see the link below) and a lichenoglyphic symbol of reversed brackets enclosing a vertical line )│( in Wunnumin Lake, Ontario. The same symbol is painted on other rocks.7,8
I wonder if our ancestors may have created lichenoglyphs, either as a community act or a personal act of devotion. After all, it’s easy to scratch lichens away to create a symbol, such as the iconic spirals, rings or arcs of British rock art. And it would probably last for years. This is, of course, pure speculation. But there’s no doubt that lichens are an important, but often unapproached, almost subliminal element in our sacred landscapes. The next time you’re at a megalithic site take a closer look at these fascinating organisms and wonder what stories their longevity would allow them to tell.
- Benedict, J B. A review of lichenometric dating and its applications to archaeology American Antiquity 2017:74:143-172
- Lutzoni, F & Miadlikowska, J. Lichens. Current Biology 2009:19:R502-R503
- Malter, J & Powell, M. The lichens of the Rollright stones. British Lichen Society Bulletin 2016 (winter):54-66
- Sparrius, L & Aptroot, A. Changes in the lichen flora of megalithic monuments in the Netherlands, in Lichenological Contributions in Honour of GB Feige; Bibliotheca Lichenologica Vol.86. Jensen, M. (ed.) 2003, Schweizerbart Stuttgart. pp.441-452.
- de Vera, J-P, Alawi, M, Backhaus, T et al. Limits of life and the habitability of Mars: The ESA space experiment BIOMEX on the ISS Astrobiology 2019:19:145-157
- Richardson, D. The Vanishing Lichens: Their History, Biology and Importance. 1975, David and Charles. p.20, 47, 55-58, 69-70.
- Dewdney, S. & Kidd, K. Indian Rock Paintings of the Great Lakes. 1962, Univ. of Toronto Press p.43, 74-75.
- Saskatchewan Archival Information Network. Thunderbird Lichenoglyph.
Published in NE162 (December 2020), pp.13-15