Species of the Month September 2022

Sycamore Tarspot (Rhytisma acerinum)

Sycamore Tarspot is a fungus which causes raised black spots to appear on the leaves of Sycamore (Acer pseudoplatanus). Spores are produced in spring and attach themselves to new leaves as they form. The fungus then develops into the black spots in late summer and autumn, so now is an excellent time to see it.

Sycamore Tarspot is an unmistakeable species, with nothing else making similar leaf markings. However, Tarspot fungi do affect other species of tree, so it is important to correctly identify the host. You can find out how to identify Sycamore here, and see the Welsh distribution of the tree on Aderyn. The fungi does not harm the tree, and is a sign of clean air (this fungus is particularly sensitive to sulphur dioxide air pollution).

More photos and information about Sycamore Tarspot is available on NatureSpot and FirstNature.

Sycamore Tarspot is found on Sycamore throughout south east Wales, but we only hold 400 records at SEWBReC; you can view the 1km distribution for SEWBReC here and the 10km Wales wide distribution here.

If you spot a Sycamore Tarspot during September (or at any other time of year), please send us the record, ideally via SEWBReCORD or the LERC Wales App. Instructions on how to submit records are available here.