The filamentous terrestrial alga Trentepohlia aurea first came to my attention in June 2000 when I found a large mat of it on the underside of a sloping boulder at 850m on Sgurr Eididh nan Clach Geala (NH256842) in the Beinn Dearg range. Identifying it was a bit of a problem, but eventually with the help of the late Prof. Douglas Henderson it got a name. As often happens in these situations, the species caught my imagination and I began to see it all over the place, emphasising that one can go for along time seeing interesting things without them actually registering! The excuse is that we have so much by way of interesting flora and fauna in this area that no-one can be on top of everything.

Trentepohlia is a genus of terrestrial green algae (i.e. they contain chlorophyll) which appear reddish-orange because of the masking carotenoid pigments. Several species occur in Britain. Some details can be obtained from Alan Silverside's web site. Exact identification can be obtained only with the aid of a microscope, and not all of my records can be ascribed to T. aurea. On ecological grounds (especially the dominance of records from stone substrates) in seems likely that most, if not all, are that species. It is very much associated with shaded, humid conditions, and is frequently abundant on the north-facing side of bridges while absent or much scarcer on the south-facing side. Most records are from mortared masonry, but I have also found it on limestone rocks, and on earth or moss in close proximity to these situations. I have infrequently found the similar but less robust T. abietina which normally grows on tree bark, and twice encountered T. umbrina at altitudes of 800-913m in Perthshire (see maps).

Trentepohlia is the photobiont for a number of lichens.

Trentepohlia aurea on a concrete wall at Strathpeffer NH45. The whitish areas within the main mass of alga, also visible at the top right of the close-up photograph below, are probably an infection of the alga by the fungus Athelia sp., either A. arachnoidea or A. epiphylla.  I am grateful to Malcolm Storey who offered this information.

Photos © Murdo Macdonald.

Above: Trentepohlia aurea on a concrete wall at Strathpeffer NH45, showing the cushions of aerial filaments.

Right: Details of filaments of Trentepohlia aurea from Sgurr Eididh nan Clach Geala. T. aurea can be recognised by its cylindrical cells unconstricted at the cell boundaries, and its wide (>10μm) filaments. Internal cell details are not shown.