After several nights of -7C here in this north Pennine valley, the trees are leafless, the thistles, docks and other wild plants collapsed and frost-browned. The following thaw has made the earth sticky and heavy, and my boots collect mud as I walk. My way leads past an old farmhouse, its gravel drive made of large chunks of whinstone, grey and hardwearing. With the wet, the trod path has erupted with alien shapes like congealed lumps of glue. This curious life form, neither fungus nor algae, is Nostoc commune.
A form of cyanobacteria, nostoc retreats into dormancy in dry conditions, shrivelling to a dark, crusty, dead-looking mat, and can stay like this for long periods. Revived when wet, it swells into a bumpy gelatinous mass. No wonder that it was given names evoking the mystery of its origins: star jelly, witches’ butter, mare’s eggs, spit of moon, fallen star.
The name “nostoc” was invented in the 16th century by the Swiss physician and alchemist Paracelsus. A compound of English and German words, the word references the nostrils because of nostoc’s green mucusy appearance, its “excrement blown from the nostrills of some rheumantick planet”.
Nostoc is weirdly fascinating. I hunker down to take a closer look. Some patches are like creeping blobs from a sci-fi horror film, others look as harmless as seaweed tossed up on a beach. In places it is as dark and shiny as a frog’s back, in others it is swirling and honey-coloured, like the top of a toffee bun.
It’s the compaction created by walkers and cars that have led to the conditions in which nostoc can thrive. Growing alongside it I see pearlwort and liverwort – two other plants that grow where there’s poor drainage. Once you become aware of it, you notice it everywhere: by roadsides, in lawns, on concrete and paving.
Nostoc exists worldwide. It is ancient and tenacious. It can fix nitrogen from the atmosphere and can photosynthesise, making it self-sufficient of other organisms. Cyanobacteria can withstand extremes of temperature and there are species living near live volcanoes and in the Arctic. Unsurprising, then, that compared with the rest of the valley’s plants, this resilient survivor is completely untouched by the recent frosts.
• Under the Changing Skies: The Best of the Guardian’s Country Diary, 2018-2024 is published by Guardian Faber; order at guardianbookshop.com and get a 15% discount
