Among the many lichens that decorate our trees and hedgerows is Evernia prunastri—better known as oakmoss. Soft to the touch, pale green in colour and often mistaken for a fruticose species, it hangs from twigs like miniature seaweed. Yet this is, in fact, a foliose lichen, cleverly attached at a single point so that it appears fruticose.
Click the image to access the full species description and glossary.
How to Identify Evernia prunastri
Although it looks shrubby, Evernia prunastri is a foliose lichen with a distinctive, flattened thallus and a clear difference in colour between the two surfaces: pale green to grey‑green above and whitish below (Fig.1).
- Lobes: Flat, neatly branched and often show fine longitudinal ridges (Fig.3), typically 3–5 cm long and 2–3 mm wide.
- Older lobes: May twist or curl, sometimes showing greenish patches on both upper and lower surfaces.
- Soralia: Present along the lobe margins—powdery, pale, and the main reproductive feature.
- Fertility: Very rarely fertile; apothecia are extremely uncommon in Britain. Instead, the species relies predominantly on asexual reproduction via soredia, which are produced in discrete soralia on the thallus surface. Soredia can be observed in the Fig. 7 video below.
For a full species description and glossary, click here or on the picture above.
Fig. 1 The pale, whitish underside of Evernia prunastri, a key identification feature (Image credit: Jagoda Zajac, MKNHS)
Fig. 2 . Evernia prunastri on a twig—its hanging, shrubby appearance disguises its true foliose nature. (Image credit: Jagoda Zajac, MKNHS)
Fig. 3 . Close‑up of Evernia prunastri revealing the characteristic ridged texture of its flattened lobes. (Image credit: Jagoda Zajac, MKNHS)
Chemical and UV Tests
Chemical spot [2] tests can help confirm identification, especially when distinguishing Evernia from similar species.
Medulla: C–, K–
When a small area of the medulla (the soft, cottony inner layer revealed by gently scratching the surface) is touched with C (Milton Sterilising Fluid) or K (Caustic Soda), no colour change occurs. (Fig.4)
Cortex: K+ yellow, C–, UV–
The cortex (the outer “skin” of the lichen) reacts differently. When K (caustic soda) is applied, the cortex turns yellow, a positive reaction caused by the presence of usnic acid. The cortex shows no reaction to C (bleach) and does not fluoresce under UV light. (Fig. 5)
This combination of soft texture, two‑toned colour, and flattened branching makes Evernia prunastri distinctive once familiar.
Fig. 4 Spot‑test demonstration on Evernia prunastri: the cortex turns yellow with K but shows no reaction with C, while the exposed medulla remains negative to both tests. (Image credit: Jagoda Zajac, MKNHS)
Fig. 5 Evernia prunastri under 365 nm UV light: both the thallus and the K‑reaction spot remain UV–, while nearby Lecidella elaeochroma fluoresces, showing a clear UV+ response. (Image credit: Jagoda Zajac, MKNHS)
Similar Species and How to Tell Them Apart
Several lichens can be confused with Evernia prunastri, especially at a glance. The most common lookalikes are species of Ramalina and Pseudevernia (Fig.6). Ramalina farinacea has more regular, strap‑shaped lobes with neat, oval soralia along the edges, and it feels noticeably stiffer. Ramalina fastigiata grows more upright, with narrower, more cylindrical lobes and soralia that are often terminal. Pseudevernia furfuracea differs again: grey‑green above but dark or blackened below, with thicker, more irregular lobes and none of the soft, two‑toned delicacy of Evernia.
Importantly, Evernia prunastri is the only species of its genus found in Britain and Ireland, which simplifies identification once you know its key features
Fig. 6 Comparison of Evernia prunastri with the look‑alike species Ramalina farinacea and Ramalina fastigiata. Ramalina is a true fruticose lichen (from Latin frutex, meaning shrub or bush). Pseudevernia furfuracea is another similar species but it is in decline across the South‑East and has not been recorded from Milton Keynes on the BLS interactive maps. (Image credit: Jagoda Zajac, MKNHS)
Reproduction and the Mighty Mites
Fig. 7 Two mites walking across the soralia of Evernia prunastri, feeding and helping to disperse its powdery soredia. Recorded under the microscope at 100× magnification. (Image credit: Jagoda Zajac, MKNHS)
One of the most charming ecological stories involving Evernia prunastri comes from the world of mites. According to the British Lichen Society’s Mighty Mites article [1], these tiny creatures are primary consumers of lichens feeding directly on the soredia. In doing so, they provide a remarkable service: their faeces contain both fungal spores and algal material, effectively packaging the partners together. This makes mites surprisingly efficient dispersal agents, helping the lichen establish on new twigs and branches.
As they move across the thallus, mites become coated in soredia—the tiny powdery propagules containing both the mycobiont (fungus) and photobiont (alga). This means mites act as ready‑made dispersal agents, carrying soredia with them as they travel and helping the lichen colonise areas.
Ecological Significance
- Indicator of air quality: Moderately pollution‑tolerant but still associated with relatively clean air.
- Microhabitat provider: Shelters mites, springtails, spiders, beetles and other tiny invertebrates. (Fig.8)
- Nest material: Long‑tailed tits often use Evernia to line their beautifully camouflaged nests.
Fig. 8 Various invertebrates making use of Evernia prunastri’s soft, branching thallus (Image credit: Jagoda Zajac, MKNHS)
Cultural and Historical Uses
Oakmoss has a surprisingly rich human history [3]:
- Perfumery: A classic base note in traditional fragrances, valued for its earthy, mossy scent.
- Dyeing: Used historically to produce soft greens and browns.
- Wigs and hygiene: According to Dobson, it was once ground with rose petals to make hair powder—used to whiten wigs, mask unpleasant odours, and even kill head lice.
- Food: In parts of the Middle East, it was added as a flavouring to bread.
- Shotguns: It has even been used as wadding in old‑style firearms.
Fig. 9 A graphic illustrating the many uses of Evernia prunastri, from perfumery and dyeing to historical food flavouring and even shotgun wadding. (Image credit: Jagoda Zajac, MKNHS)
Why It Matters
Evernia prunastri is a species that rewards close attention. It plays a role in everything from woodland ecology to cultural history. In Milton Keynes—where green spaces thread through the urban landscape—oakmoss reminds us that biodiversity thrives in the small details: on a sunlit branch, a hedgerow gate, or a quiet corner of a footpath. The image to the right shows a Sorbus (Rowan) trunk in Old Farm Park, Milton Keynes, densely covered in Evernia prunastri, a perfect example of how this lichen flourishes in unexpected places.
Jagoda Zajac, February 2026
References
- British Lichen Society. British Lichen Society Bulletin. 2025; p.23. BLS_Summer_2025_Bulletin.pdf
- British Lichen Society. Chemical tests [Internet]. Available from: https://britishlichensociety.org.uk/learning/chemical-tests
- Dobson F, Lichens. An Illustrated Guide to the British and Irish Species. The British Lichen Society. 2018 p.186
- Whelan P. Lichens of Ireland and Great Britain. A Visual Guide to Their Identification
Volume II. Holm Oak Press; 2024. p.647 Yahr R, Stoakley J, Lichens of Great Britain and Ireland. An introductory Guide. Bloomsbury; 2025. p.131
