Nostoc

After a shared chocolate croissant at the cafe we went to play hide-and-seek in the abbey ruins. The two-year-old spotted some gelatinous brown bubbles on the mortar between the ancient stones - easy to assume someone had been throwing seaweed around but I recognised it as nostoc, a peculiar life form which is not algae or fungi or slime mould or lichen but  bacterial in original. It has puzzled people for centuries and attracted names such as star jelly and plant snot. It annoys home owners by growing on lawns and concrete paths - but in parts of Asia, Africa and S. America it has long been prized as a useful food, especially as it can be dried and rehydrated.
Some modern health practitioners extol nostoc as a potential superfood...

 Latterly however nostoc cyanobacteria  has been implicated in the aetiology of neurodegenerative diseases in humans. Oliver Sacks, the great writer and neurologist, went to the island of Guam to research a mysterious and very unpleasant terminal illness that affected the islanders. He and his colleagues identified as its probable causation  the presence of nostoc in the human food chain,  arriving not by direct consumption but via other dietary items.

For anyone else as curious as I am about such matters I recommend Oliver Sachs book The Island of the Colour Blind about this and much else. And if you're tempted to sample nostoc there is both a recipe and a dire warning here.

For a prettier sight, see the nostoc-spotter as extra