The bark of some trees on the Common has an incrustation of the green alga Trentepohlia. It occurs on the trunk of a sallow tree growing in a thickly populated group of Salix caprea, S. cinerea and hybrids, and on a wild plum, again in a thicket of an abandoned hedge (See photos below). The patches of the alga may be up to 25 x 100 cm, usually on one side of the trunk only; the colour varies from yellowish orange to brick red. Even though the trees are probably quite old, the bark is relatively smooth and the sallow has not developed the deep fissuring sometimes seen in mature S. caprea.

This year the alga was also seen growing in the open on an area of depauperate heather and stony, sandy bare ground. Early in March S.F., looking for fungi, noticed a widespread, brick red layer, usually spreading from a stunted heather plant over the bare sand. By the time it had been identified and photographed early in April, it had largely dried up and was confined to the heather clumps. It has now (late May) disappeared altogether.

Although a green filamentous alga it appears reddish in colour, due to the orange pigment, haematochrome (ß-carotene), which hides the green of the chlorophyll. Trentepohlia is also a widespread photosynthetic photobiont in lichens. (A good web site for more information is: www-biol.paisley.ac.uk/bioref/Chlorophyta/Trentepohlia.html) The species was identified as Trentepohlia umbrina by Dr Hilda Belcher who described its distribution mainly in the West and North West of the country. More recently she has found it on a Tulip tree in a Cambridge College garden (to be written up in ‘Nature in Cambridgeshire’) and has learnt that Professor Bate and a research student are researching its apparent spread in the south of England, possibly in response to the decrease in SO2.

Dr Belcher has suggested that this note may produce new records, so keep your eyes open for more!