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This brown scum that thrives in our wet winters is called Nostoc Commune

Anticipating cultured conversation after a local theatre performance, we retired to the bar for a night cap. But as this is a rural area, talk was all about an entirely different type of culture – a strange gooey, gunky and shiny brown growth.

I’d first spotted it while being a marshal for the Rally of New Zealand. After poking it with the toe of my boot, I decided it resembled seaweed or pond scum – except it was flourishing in roadside gravel. A while later, there it was again – gleaming (in a rare spot of sunshine) on our drive.

That night after the play, I was in the company of many seasoned farmers – who had all spotted its recent arrival, but knew nothing about it.

“I’ll do the research,” I said, “and let you know.”

Northland Regional Council’s biodiversity specialist double-checked with NIWA’s algal experts who confirmed it’s Nostoc commune, commonly called Blue Green Algae.

A mind-dizzying visit to Wikipedia and thereabouts taught me it’s a type of cyanobacterium (blue bacteria) which can live in salt and fresh water, soil and, as we know for a fact, bare rock.

As well as finding out spirulina belongs to the extended family and that there are countless types with long and scientific names, I also know this: “They are Gram positive prokaryotes. They are photosynthetic and have pigments like chlorophyll a, carotenoids, along with phycobilins. They have autotrophic mode of nutrition.” And on and on. Knew you’d be fascinated.

The Nostoc thriving in Kaipara may be the strain known as fallen star or star jelly. It can fix nitrogen, reclaim soil and is so hardy that, after lying dormant for ages, it grows again when exposed to water.

You can, apparently, kill it with various things: salt, vinegar, copper sulphate, dairy alkali cleaner XY12 (full strength or one part to two of water) or possibly glyphosate or algae killer.

As some strains of cyanobacteria are highly toxic, I’d recommend you do more research before you use Nostoc as a food supplement which is what they do in China.

Several people have since told me they reckon it grows where glyphosate (better known by the brand name Roundup) has been sprayed. More research is underway. Stay tuned.