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Evernia prunastri – Oakmoss, the Soft Green Lichen of Milton Keynes – Jagoda Zajac

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

  1. British Lichen Society. British Lichen Society Bulletin. 2025; p.23. BLS_Summer_2025_Bulletin.pdf
  2. British Lichen Society. Chemical tests [Internet]. Available from: https://britishlichensociety.org.uk/learning/chemical-tests
  3. Dobson F, Lichens. An Illustrated Guide to the British and Irish Species. The British Lichen Society. 2018 p.186
  4. Whelan P. Lichens of Ireland and Great Britain. A Visual Guide to Their Identification
    Volume II. Holm Oak Press; 2024. p.647

  5. Yahr R, Stoakley J, Lichens of Great Britain and Ireland. An introductory Guide. Bloomsbury; 2025. p.131

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Xanthoria parietina: The Sunshine Lichen of Milton Keynes – Jagoda Zajac

Few lichens are as instantly recognisable as Xanthoria parietina, often known as the Common Orange Lichen, Yellow Wall Lichen or simply Sunburst Lichen. Its brilliant colour, remarkable resilience and ability to thrive on everything from twigs to metal signs make it an ideal introduction to the ten most common lichens found on our local trees.

Click the image to access the full species description and glossary.

Form, Colour and Growth

Xanthoria parietina is a leafy (foliose) lichen, meaning its body forms broad, leaf‑like lobes that sit loosely on the surface rather than lying flat and crust‑like (crustose). This structure makes it easy to spot and easy to lift gently at the edges—one of the features that distinguishes foliose lichens from crustose species that are firmly glued to their substrate. Unlike fruticose lichens, which are the same colour all around, foliose lichens have two distinct surfaces: an upper surface rich in pigment and an underside that differs in colour and texture.

X.parietina is best known for its orange‑yellow colour, produced by parietin, a pigment concentrated in the outer cortex. Parietin acts as a natural sunscreen, shielding the lichen’s algal partner from intense sunlight and ultraviolet radiation. The thallus shows a stronger yellow colour in well‑lit spots, shifting toward greener tones in shade. (Fig.1)

Fig. 1 Three thalli of Xanthoria parietina showing how light shapes their colour: a vivid golden yellow in full sun, a softer orange in partial shade, and a greenish tone where light is limited. (Image credit: Jagoda Zajac, MKNHS)

The thallus is typically lobed and can reach up to 15 cm across in older specimens. As it ages, the centre may die back, forming rings or arcs that help identify mature individuals. The underside is white, with short rhizines that anchor the lichen to bark, stone, or metal. (Fig.2)

Reproduction is mainly through apothecia, the orange discs scattered across the surface. These are concave when young and become flatter with age. The species lacks soredia and isidia, so it relies on spores and fragmentation. Growth is generally slow—around 2.6 mm per year—though moist, cool habitats can support faster expansion, while dry or exposed sites slow it down. Growth typically peaks in autumn and winter when conditions are wetter.

Fig. 2 White underside of Xanthoria parietina showing its foliose, leaf‑like form, with the circular inset revealing the tiny rhizines that anchor the lichen to its substrate.  (Image credit: Jagoda Zajac, MKNHS)

Chemical and UV Tests

Chemical spot tests and UV examination are standard tools in lichen identification and in the video below I demonstrate how Xanthoria parietina responds to them.

The C test uses fresh bleach (such as Milton Sterilising Fluid) to check for lichen substances that react with sodium hypochlorite; if present, the spot shows a quick colour change, but many species—including Xanthoria parietina—remain C–. The K test uses a solution of potassium hydroxide or caustic soda to detect compounds that react with alkali, often producing red or purple colours; in Xanthoria parietina, the reaction is K+, it begins with a red‑orange hue and develops into a vivid crimson‑purple.[2]

Fig. 3 Chemical spot tests on Xanthoria parietina at Caldecotte, MK; no reaction with the C test, but an immediate K+ reaction (Image credit: Jagoda Zajac, MKNHS)

Under a 365 nm UV torch, the thallus shows a bright yellow‑orange glow. This is mainly due to strong reflectance from the parietin pigment, with only weak true fluorescence. Because the glow is obvious, the species is usually recorded as UV+ (orange), even though the effect is not classic fluorescence.

Fig. 4 Under 365 nm UV, the thallus of X.parietina shows a vivid orange glow from its parietin pigment, though this is mostly reflectance rather than strong fluorescence; Linford Wood, MK (Image credit: Jagoda Zajac, MKNHS)

Habitat, Nitrogen Tolerance and Ecology

Xanthoria parietina is strongly associated with nitrogen‑rich environments. Its tolerance of elevated nitrogen allows it to thrive in areas influenced by traffic, agriculture, or general urban activity. It grows on an impressive range of surfaces—including wood, stone, metal and has even been recorded on rabbit bones, a striking reminder of its ability to colonise unusual substrates.[1]

Fig. 5 Three different habitats for Xanthoria parietina: thriving on a twig, spreading across stone, and even colonising a painted metal sign. (Image credit: Jagoda Zajac, MKNHS)

Ecologically, Xanthoria parietina is a miniature ecosystem in its own right. It is one of the most frequently parasitised lichens in Britain, hosting an impressive diversity of lichen‑dwelling fungi.[3] . An example of these fungi is shown in Fig. 1, in the central photograph, where they appear as black spots on the apothecia.

Its thallus also shelters tiny animals such as rotifers and provides food for gastropods. 

Extreme Survival: Xanthoria in Space

Xanthoria parietina has attracted scientific attention for its extraordinary resilience. In experiments simulating outer space, it survived exposure to vacuum, cosmic radiation, and dramatic temperature swings. Its ability to endure such extremes has made it a model organism in astrobiology, raising fascinating questions about the limits of life and the potential for survival beyond Earth.[5]

Natural Dyeing

Lichens have a long association with natural dyeing and Xanthoria parietina is no exception. Its vivid parietin pigment produces warm yellow to orange tones when extracted, especially with an alum mordant to help fix the colour to fibres. While some experimental dyers report pink or lavender shades under strongly alkaline or ammonia‑fermented conditions.

Spotting Xanthoria parietina Around Milton Keynes

For anyone exploring the trees, parks, and footpaths of Milton Keynes, Xanthoria parietina is a bright and reliable companion. Widespread across the MK and beyond, it’s one of the easiest lichens to recognise—its vivid colour, abundance, and ecological significance make it an ideal starting point for beginners. And while you certainly don’t need chemical tests or UV lamps to appreciate it, those little experiments simply reveal how much quiet magic even our most familiar lichens can hold.

For more information visit Xanthoria parietina | The British Lichen Society.

Jagoda Zajac, January 2026

References

  1. British Lichen Society. British Lichen Society Bulletin. 2019;125:41. BLS Bulletin 2019 Winter.pdf
  2. British Lichen Society. Chemical tests [Internet]. Available from: https://britishlichensociety.org.uk/learning/chemical-tests
  3. British Lichen Society. Lichenicolous fungi occurring on Xanthoria parietina in the United Kingdom 2024. Available from: Guide – LFs on Xanthoria parietina
  4. Dobson F, Lichens. An Illustrated Guide to the British and Irish Species. The British Lichen Society. 2018
  5. Lorenz, C., Bianchi, E., Benesperi, R., Loppi, S., Papini, A., Poggiali, G., & Brucato, J. R. (2022). Survival of Xanthoria parietina in simulated space conditions: vitality assessment and spectroscopic analysis. International Journal of Astrobiology, 21:3 137–153 https://doi.org/10.1017/S1473550422000076
  6. Whelan P. Lichens of Ireland and Great Britain. A Visual Guide to Their Identification
    Volume II. Holm Oak Press; 2024. p.621

  7. Yahr R, Stoakley J, Lichens of Great Britain and Ireland. An introductory Guide. Bloomsbury; 2025. p.139

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Lichens in Milton Keynes – Jagoda Zajac

Walk through any park, street or woodland in Milton Keynes and you’ll find them quietly thriving: lichens. They are everywhere—on tree bark, stone walls, pavements, rooftops and even metal street signs. Yet most of us pass them by without a second glance.

Lichens are extraordinary organisms, formed through a partnership between fungi and algae (or sometimes cyanobacteria). This collaboration allows them to survive in places where few other life forms can. They play a vital ecological role: creating microhabitats for insects, providing food for slugs and snails, supplying nest material for birds, and even helping us understand patterns of air pollution through the species that thrive or decline in different conditions.

Fig. 1-6 A tree trunk holds far more than its bark suggests. Look closer and a living mosaic comes into view: the fine grey rosettes of Physcia tenella, the golden patches of Xanthoria parietina and the pale crusts of Lecanora chlarotera s.lat. Together they form a miniature community, showing how much life thrives on a single tree. Click on the images for a closer look. (Image credit: Jagoda Zajac)

But here’s the challenge—identifying lichens is notoriously difficult. Their shapes are subtle, their colours shift with moisture, and many species look deceptively alike. Proper identification often requires chemical spot tests to see if colours change, microscopic examination of spores or crystals in fruiting bodies, and even checking their reactions under ultraviolet light. To make things trickier, lichens are constantly being reclassified as scientific understanding evolves, with names and genera shifting in the taxonomic system. For beginners, this can feel daunting.

The good news? Some lichens are distinctive and easy to recognise once you know what to look for. These “gateway species” are perfect starting points for anyone curious about the hidden biodiversity around us.

Over the coming months, I’ll explore ten of the most common lichens found on trees in Milton Keynes. Each article will highlight a species, offering tips on recognition, ecological significance, and the stories they tell about our environment. I’m still learning myself but I hope this series will be a chance for both you and me to discover more about lichens together.

Jagoda Zajac, December 2025

Top photo: Ramalina fastigiata catching November sunshine (Credit: Jagoda Zajac)

Lichens of Milton Keynes: Discover the 10 Most Common Species on Trees

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