Barnacle lichen (Thelotrema lepadinum)

What does barnacle lichen look like?

Lichens are organisms formed by the symbiosis of a fungus species and one or more other organisms, most typically an alga.

Thelotrema lepadinum is a crustose lichen, which forms creamy grey-white crusts on the surface of tree bark. It is characterised by its apothecia (the fruit body which produces the spores) as they resemble barnacles.

Not to be confused with: other whitish ‘crustose‘ lichens growing on trees, like the Pertusaria lichens (e.g. Pertusaria hymenea and Pertusaria leioplaca). In the extreme west of the UK, two rarer species of barnacle lichen (Thelotrema petractoides and T. macrosporum) can occur, on smooth bark (like hazel and young ash) in wet oceanic woodlands.

Where to find barnacle lichen

Barnacle lichen can be found throughout the UK and Ireland, and particularly in areas with more ancient woodland. It is most frequent in well-wooded parts of southern and southwest England, Wales and the Welsh Marches, northern England and Scotland. Look closely at tree trunks in old woodlands in these areas.

Value to wildlife

Lichens play an important role in the ecology of woodlands. Lichens on trees provide important microhabitats, shelter and food for various small invertebrates. These in-turn are prey for larger insects and birds.

They can also be hosts for other species of parasitic fungi. Lichens also provide many other ecosystem services such as carbon cycling and water retention.

Uses of barnacle lichen

Although barnacle lichens probably have no known uses, lichens have been used throughout history as sources of food, medicine and as a dye.