There was blue sky over the fells this week when we visited the River Ehen for another of our monthly visits. The first impression today was that the riverbed was much less green. The cobbles still had a thick, slimy film but there was less of the Spirogyra and Draparnaldia that characterised the samples from January and February. Another absentee was the thick growths of the red alga Audouinella hermanii although another red alga was very abundant at the same site: this was Lemanea, which forms wiry filamentous growths on stones submerged in the fastest-flowing parts of the stream. Once again, however, this so-called red alga is actually olive-green in colour. At some point in the near future, I must post some pictures of a red alga that really is red.
Lemanea fluviatlis attached to a boulder from the River Ehen, April 2013.
In close up, Lemanea does not form the flaccid limp filaments of Spirogyra and other green algae that are just a single cell thick. These are multicellular, a couple of millmetres thick at the base and tapering gradually to a point. Many years ago, I cut a thin section from a filament of Lemanea and stained it with the fluourescent dye Calcofluor-white, which binds to the cell walls. This photograph shows very clearly how the cells form a tube around a hollow core to give a streamlined form that can thrive in those parts of the stream where the physical stresses are greatest.
A section through a filament of Lemanea from the River Wear, stained with the fluorescent dye Calcofluor-white.
I was surprised to read that this unprepossessing plant was eaten in some parts of eastern India although, as Lemanea is a distant relative of Porphyra umbilicaris, the alga from which lava bread is made, perhaps I should not have been. The first paper I read on this topic contained few details and my own experiments, washing the filaments and chopping them over a salad met with less-than-ecstatic responses from friends and family. However, I subsequently found another paper which gave more details. As the alga is only abundant for a few months in the year, it is harvested and air-dried so that it can be stored. Then it is cooked with vegetables to impart a fishy flavour. This description gives the impression that it is used like a herb, adding flavour to the dish, rather than as a significant source of nutrition itself. Time, perhaps, to think up some new recipes? In the same way that samphire complements seafood dishes perhaps Lemanea would raise the flavour of trout or other delicately-flavoured freshwater fish? My main problem may be persuading people that the dish I have served them really is a gastronomic treat and not just a pile of algae I pulled out of a local stream …