A local lichenologist alerted me that she had seen an Usnea ariculata on the South Downs Way near the Devil's Dyke, West Sussex (South Downs National Park). She sent me the OS grid reference and a description of its location. This is a rare species in the South East so I was keen to see it.
There are many individual and small groups of Hawthorne tress at Waterhall, as there are on many South Downs dip slopes and in hedgerows. These Hawthornes were covered in lichens including Lecidella elaeochroma, Ramalina farinacea, Ramalina fastigiata; Xanthoria parientina
In a stand of Hawthorns I saw this beautiful and large Usnea ceratina
Whilst Usnea articulata is easy to identify, because of its distinctive morphology, other Usnea ("rope-like") species are less easy to identify. Many of the species are morphologically variable and can be difficult to identify. The medullary tests are useful in separating some species but in many cases thin layer chromatography is needed to be certain. Frank S Dobson, Lichens: An Illustrated Guide to the British and Irish Species (2018) p, 461. I have identified this as Usnea ceratina as the best fit to the Usnea key and species descriptions in ibid. p. 461-470; but it is not a perfect fit to the description of Usnea ceratina in Dobson
Usnea ceratina, on Oak bough, pasture woodland, Mark Ash, New Forest © Neil A Sanderson
Horsehair lichens have a high surface area to mass ratio, allowing them to filter moisture and elements from the air. On the flipside, this leaves them vulnerable to a whole host of atmospheric pollutants, from sulphur dioxide which gets spewed out of some heavy industries, to high levels of reactive nitrogen compounds from diesel car exhausts and agriculture. So if you see horsehair lichens, which are big and bushy, it’s a sign you’re breathing clean air! Sulphur dioxide has declined a lot in the UK, however nitrogen pollution, though declining steadily, is still an issue – a recent report found that in 2018, critical loads for nutrient nitrogen (a deposition rate below which significant harmful effects on a sensitive habitat are not expected to occur) were exceeded in 58.9% of nitrogen-sensitive habitats in the UK.
From Waterhall, I walked on to the Devil's Dyke and on the South Downs Way, on the south side of the scarp slop of the Dyke, I found the Usnea ariculata on a Hawthorn.
This species was very sensitive to sulphur dioxide pollution and declined in the 19th and 20th centuries. It ... is showing signs of recovery subsequent to declines in sulphur dioxide pollution, especially in south Wales. British Lichen Society Usnea articulata
Whilst Usnea aticulata is recovering, it is still rare in the South East
British Lichen Society distribution map:
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I am grateful to receive corrections if I have made an identification error.