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Physcia adscendens and Physcia tenella: Two Urban Lichens Worth Getting to Know – Jagoda Zajac

If you spend any time looking closely at the twigs of street trees or hedges, the surface of a weathered fence panel or even metal man-made objects, you will almost certainly encounter two of Milton Keynes’ most familiar lichens: Physcia adscendens and Physcia tenella. They are small, grey foliose lichens that thrive in the bright, nutrient enriched conditions typical of towns. Although easy to overlook at first, they quickly become recognisable companions once you learn their shapes and habits.

For full species description and glossary click on the PDF image or click here.

Distribution and Urban Habitats

Both species are widespread across Milton Keynes and can be found on a variety of substrates. They are particularly noticeable on hawthorn and weathered fence panels in Milton Keynes. But they happily also conquer the plastic, metal signs and concrete posts. No matter where you are in MK, you will spot them at every corner. Their success reflects their tolerance of mild nitrogen enrichment from traffic, fertilisers and bird activity. 

Fig. 1.  Physcia species growing on a twig, a rose hip and a sycamore seed. The rose hip and sycamore seed were photographed in Joe Clinch’s garden when he kindly opened it to the MKNHS members to see his flowering fritillaries. (Image credit: Jagoda Zajac, MKNHS)

Fig. 2.  Physcia species growing on man‑made structures, including a plastic rope near the Cruck Barn, a metal gate – visible as the silver, speckled patches – and a wooden fence. (Image credit: Jagoda Zajac, MKNHS)

Key Identification Differences

The most important difference between the two species lies in the shape of their lobe tips (Fig. 3 and Fig. 4). Physcia adscendens is instantly recognisable once you learn to spot its distinctive hooded lobes. The tips of the lobes inflate into small-helmet-like hoods, where the soralia develop, which release the tiny reproductive propagules called soredia (Fig 5). These hoods give the species a slightly three-dimensional, pocketed appearance around the margins.

In contrast, Physcia tenella has lip-shaped lobe tips. Instead of forming hoods, the lobe ends turn back to create open, powdery soralia that look like tiny pale mouths. This difference—hoods versus lips—is the most reliable way to separate the two species in the field.

However, you may sometimes find specimens that clearly belong to the P. adscendens–P. tenella pair but still can’t be confidently placed in one species. This often happens when young thalli haven’t developed their distinctive soralia, or when the material is too poorly developed to interpret reliably.

Fig. 3.  Comparison of Physcia adscendens and Physcia tenella, showing the contrasting lobe‑tip structures that distinguish the two species. (Image credit: Jagoda Zajac, MKNHS)

Fig. 4.  Close‑up views of the lobe‑tip regions shown in Fig. 3, illustrating the hooded soralia of P. adscendens and the lip‑shaped soralia of P. tenella.(Image credit: Jagoda Zajac, MKNHS)

Fig. 5.  Physcia adscendens showing the characteristic hooded lobe tips with soredia developing beneath the hoods. (Image credit: Jagoda Zajac, MKNHS)

Both Physcia adscendens and Physcia tenella are capable of producing apothecia (Fig.6) which are the disc‑like fruiting bodies that release sexual spores. In Physcia, they typically appear as black (P.adscendens) and dark brown (P.tenella) discs with a paler, slightly raised margin. P. tenella tends to produce apothecia more readily, sometimes quite abundantly in older thalli, whereas P. adscendens forms them less frequently. When present, apothecia add another layer of texture to the thallus and can be a useful feature for confirming identification.

Fig. 6.  Comparison of the apothecia of Physcia adscendens and Physcia tenella, showing the differences in their colour, frequency and overall appearance. (Image credit: Jagoda Zajac, MKNHS)

Morphological Features

Morphologically, the two species share many features typical of the genus Physcia. They form small rosettes, usually between one and five centimetres across, with a grey upper surface. Both species have marginal cilia, the fine hair-like projections that fringe the lobe edges (Fig. 7). Their purpose is not entirely clear. Sometimes the cilia grow from one lobe and connect to another, helping to steady the lichen in the wind. This lets air move freely around the lobes which prevents them from becoming waterlogged.

Fig. 7.  Physcia tenella showing the marginal cilia and the black pycnidia scattered on the lobes. (Image credit: Jagoda Zajac, MKNHS)

You may also notice tiny black dots on the lobe tips or margins: these are pycnidia, structures that produce asexual spores (Fig.7). The pale speckles scattered across the upper surface are maculae (Fig. 8). They occur where the algal layer is thinner or absent, allowing the pale fungal layer beneath to show through. Maculae often give Physcia species a speckled or frosted look and can be useful in identification. It is worth noting that some publications refer to these pale spots as pseudocyphellae but true pseudocyphellae are actual breaks in the cortex, forming pores or slits and are not present in Physcia.

Fig. 8.  Physcia tenella showing the pale maculae clearly visible when the thallus is wet, with Xanthoria parietina on the right. Look closely for the marginal cilia. (Image credit: Jagoda Zajac, MKNHS)

Ecological Role and Air Quality

Beyond their identification, these lichens play a subtle but important role in the urban ecosystem. Their tolerance of nitrogen makes them useful indicators of air quality: their abundance suggests moderate enrichment, typical of towns but not extreme industrial pollution.

They also contribute directly to wildlife. Long-tailed tits, for example, collect fragments of Physcia and Xanthoria species to decorate the outside of their nests. The lichens adhere to the spider silk outer layer almost like Velcro, helping the nest blend perfectly with the surrounding twigs.

The Xanthorion Community

Both Physcia adscendens and P. tenella belong to the wider Xanthorion community, a group of lichens adapted to nutrient-rich, well-lit habitats. This assemblage includes genera such as Caloplaca (now often split into Flavoplaca and Athallia), Physcia, Physconia, Ramalina and Xanthoria. When you find one member of this group, you will often find several others nearby, forming a characteristic urban and suburban lichen flora shaped by light, nutrients and human influence.

Lichenicolous Fungi

Fig. 9. Physcia spp. with three lichenicolous fungi: A – Illosporiopsis christiansenii, forming pinkish patches; B – Laetisaria lichenicola, appearing as a reddish, web‑like film; C – Erythricium aurantiacum, showing its characteristic orange colouration.

Lichenicolous fungi add yet another layer of interest to these common Physcia species (Fig. 9). These are specialised fungi that live on or within lichens, often forming distinctive growths while relying on the lichen as their host. Three of the most frequently encountered lichenicolous fungi parasitising Physcia species are Illosporiopsis christiansenii, which forms soft pinkish patches on the thallus; Laetisaria lichenicola, a reddish, web‑like film that creeps across the surface; and the bright orange Erythricium aurantiacum, a striking but less common species. Lichens themselves support their own specialised communities, creating miniature ecosystems even on the smallest patch of bark or fence panel.

A Perfect Starting Point for Beginners

For beginners, these two Physcia species are ideal starting points. They are common, easy to observe without equipment, and their contrasting lobe shapes provide a clear and satisfying introduction to lichen identification. Learning to recognise them opens the door to understanding the broader ecology of lichens in Milton Keynes and helps build the confidence to explore the rest of the Xanthorion community.

I would like to thank Martin Ferns for proofreading the text and to Mark Powell for being such a great support throughout my lichen‑learning journey — helping me understand the terminology, introducing me to new species and reviewing my articles with his expert knowledge.

Jagoda Zajac, June 2026

References

  1. British Lichen Society. British Lichen Society Bulletin. Effects of hydration on the reproductive structures of Illosporiopsis christiansenii – the feasibility of a simple water-drop test in a binary field key; 2023; 132; p.15-24 BLS_Bulletin_2023_Summer.pdf
  2. British Lichen Society. British Lichen Society Bulletin. Cilia and rhizines in two common Physcia species; 2022; 130; p.20-26 BLS Bulletin 2022 Summer.pdf
  3. British Lichen Society. Physcia tenella, [Internet]. Available from: Physcia tenella
  4. British Lichen Society. Physcia adscendens, [Internet]. Available from: Physcia adscendens
  5. British Lichen Society. Lichen Ecology, [Internet]. Available from: Lichen Ecology | The British Lichen Society
  6. Dobson F, Lichens. An Illustrated Guide to the British and Irish Species. The British Lichen Society. 2018 p.352, 355
  7. Gilbert O, Lichens. The New Naturalist. HarperCollinsPublishers. 2000 p.46, 59, 166
  8. Whelan P, Lichens of Ireland and Great Britain. A Visual Guide to Their Identification
    Volume II. Holm Oak Press; 2024. p.512, 588, 591, 835, 836, 

  9. Yahr R, Stoakley J, Lichens of Great Britain and Ireland. An introductory Guide. Bloomsbury; 2025. p.180

Related Articles on Lichens in Milton Keynes

We’re Looking for a Volunteer Outreach Events Coordinator

The Society is looking for a volunteer Outreach Events Coordinator to help plan and organise our presence at local events throughout the year.

What the role involves:

  • Coordinating the Society’s involvement in outreach events run with, or hosted by, external organisations.
  • Helping organise member volunteers to represent the Society at these events.
  • Ensuring our display boards and other publicity materials are prepared and up to date for each event.

This role is ideal for someone who enjoys organising, communicating and supporting community engagement.

If this sounds like something you’d enjoy, please get in touch at info@mknhs.org.uk

Volunteers Needed for Love Wetlands Day – 21 August, 12:00–17:00

We will be hosting a Society stall at Love Wetlands Day on 21 August, from 12:00 to 17:00, at the Floodplain Forest Nature Reserve, organised by The Parks Trust. We’re looking for volunteers to help set up the stand, chat with visitors about our local wildlife and share information about the Society.

If you’d like to volunteer and support the Society at this event, please get in touch at webmaster@mknhs.org.uk

Invitation to the RSPB North Bucks Local Group 50th Anniversary on 17/06/2026

The North Bucks RSPB Local Group is celebrating a remarkable milestone—50 years young! As one of 140 RSPB local groups across the country, the group has spent half a century inspiring local people through regular talks, field trips, and public events, all centred on birds, wildlife, and conservation.

We are pleased to share that members of our Society have been invited to join the celebrations and take part in this special anniversary event.

The evening will include a short AGM followed by a talk on one of the region’s most exciting wildlife developments.

Kingsbrook: A New Model for Nature‑Friendly Living

Kingsbrook is a major new housing development on the eastern edge of Aylesbury. It represents an award‑winning partnership between the developers, the RSPB, and local councils, with wildlife‑friendly design woven throughout the project. Adjacent to the development lies Kingsbrook Meadows, a 100‑hectare nature park that will be owned and managed by the RSPB.

The evening’s speaker, Matt Hulme from the RSPB, describes Kingsbrook as:

“An inspiring example of how communities, nature, and sustainable living can come together in harmony. I hope to share the vision behind this unique development, the importance of its wildlife‑rich spaces, how it will develop over the final stages of the construction period, and opportunities to get involved in the coming years.”

Event Details

Date: Wednesday 17 June Time: 19:30–21:30 Refreshments: Provided

Venue: Whaddon Way Church Centre, Beaverbrook Court (off Whaddon Way), West Bletchley Milton Keynes, MK3 7JS

Parking

There are around 20 spaces in the shared car park opposite the church in Beaverbrook Court. If these are full, please park considerately in nearby streets and allow time to walk. Please avoid parking directly in front of the care‑home flats.

Accessibility

The venue is located upstairs but is fully accessible via a lift suitable for wheelchair users. Toilets are available on the same floor, with baby‑change facilities downstairs.

Emberton Country Park Bioblitz Invitation – June 2027

MKNHS has been contacted by the organisers of the Emberton Country Park Bioblitz in June 2027, and we are pleased to share their invitation with our members. Anyone who would like to take part is warmly encouraged to get involved. If you are interested, please contact the organisers directly at Emberton.park@milton-keynes.gov.uk.

Emberton Country Park is home to an impressive range of wildlife. The site is one of the best in the region for Odonata, supports several Biodiversity Action Plan (BAP) species, and has even produced occasional rarities such as Red‑footed Falcon and Osprey. The park also hosts several bat species, with ongoing bat‑box monitoring carried out in partnership with North Bucks Bat Group (NBBG).

A thriving moth group operates at the park, regularly recording and showcasing its findings to the public. Their success has even led to invitations to take their displays “on tour” to other venues. In addition, the park runs wildlife walks and talks helping to engage visitors with the natural world and inspire greater awareness and protection of local biodiversity.

To get the Bioblitz underway, the organisers are looking to select a suitable date in June 2027, agree a time, and gather ideas on how best to survey the site.  Once they know who wishes to attend, what equipment people may need, and any specific requirements, they will finalise the details.

If you’d like to take part, please contact Emberton.park@milton-keynes.gov.uk.

MKNHS Introduces Gift Membership

Milton Keynes Natural History Society has launched Gift Memberships, offering a thoughtful new way to share a love of wildlife with friends and family.

Buying a Gift Membership is straightforward: complete the online form and the Treasurer will be in touch to arrange payment. Once that’s done, you’ll receive a PDF gift voucher to print or email to the recipient.

Redeeming the voucher is just as simple. The recipient fills in the Online Membership Form on the MKNHS website, selects “MKNHS Gift Voucher,” and enters their voucher number. Their membership is then confirmed by email.

To purchase a Gift Membership and for more information go to Membership – Gift | Milton Keynes Natural History Society

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 apothecia that are often terminal. Pseudevernia furfuracea differs again: covered with spikey isidia, the upper surface grey‑green but the underside dark or blackened, and the lobes thicker and more irregular, lacking the soft, two‑toned delicacy characteristic 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

Xanthoria parietina
Evernia prunastri
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