It’s fairly well known that if you want to witness the glow-in-the-dark properties of our native forests, you can visit a glow-worm dell. Much less well known is that you can also visit the common tree fern Cyathea smithii and see its skirts glow with fungal bioluminescence.
Fungal bioluminescence, sometimes called fairy fire or foxfire, can be bright enough to read by, and on these ferns it can make much of the skirt glow in the dark; the trees’ own wearable art.
Last month, I joined a small group of mycologists on a mission to observe this phenomenon and collect specimens of the fungus responsible. As far as the official records went, New Zealand had no foxfire-emitting fungi, and we hoped to correct that.
We were all in Matawai, near Gisborne, attending the annual national fungal foray, and when this unusual night-time expedition was proposed, I couldn’t contain a primal yap: “Can I come?” The foray folk are very encouraging of non-scientists and I was soon stumbling through black bush with the experts.
Until that night, luminous trees had only been rumoured. A photograph of what is (incorrectly) described as fern-frond phosphorescence can be found on Naturewatch here. But the rumours were few and/or vague, and no-one knew much about these luminous trees, nor what species caused them to glow if indeed it was a fungus.
Led by Dr Peter Buchanan from Landcare Research, the party of six went to a bush track in the Matawai area. We walked in using dim torches and cellphone screens, because we wanted our eyes to adjust quickly to the darkness when we switched them off. This we did once we were under a dense forest canopy that excluded most of the moonlight.
We waited. Soon, we started to perceive wan glowing rods on the periphery of our vision. Those rods were the rachises, or spines, of the fern fronds. When a C. smithii frond dies, its rachis often remains hanging on the tree, and the rachises together form a twiggy skirt. Gradually, as our eyes convinced us, we could see on the edges of the track a ghostly display of glowing skirts.
When we approached the tree ferns, we learned three things about the glow effect:
1. The source was a fungus, and that fungus was fruiting. Teeny, tiny white mushrooms were present on the glowing twigs. The mushrooms appeared to be Mycena.
2. The mushrooms were not the only part of the organism that was glowing: most of the light came from the mycelium. Mycelium, which constitutes the matted bulk of the organism, is the part of a fungus we usually do not see, because it is under soil or bark.
3. The glowing was occuring only on the skirts and fallen rachises of this fern type. This indicated the fungus was a saprobe: one that feeds on and helps to decompose dead organic matter. Although C. smithii may not be its only host (we would later learn this Mycena had been recorded on cabbage tree skirts too), it was favouring the fern at this site.
We plucked glowing rachises from the ferns, waved them like magic wands – well, I did – and then took them back to the foray’s makeshift laboratory at the Matawai Hall. There, Landcare Research’s Dr Jerry Cooper got to work describing the species.
This particular Mycena mushroom was known: Dr Cooper had previously given it the tag name ‘Crystal Falls’, after the Otago location where it was first recorded, but no-one had bothered to describe it formally. Now that the bioluminescence of this species has been discovered, however, ‘Crystal Falls’ is well on the way to having its family tree drawn up.
The scientists are, of course, taking a precautionary approach, not wanting to declare prematurely that the country’s fern forests glow in the dark.
But I want to declare that. The host fern is common throughout the land. The ‘Crystal Falls’ fungus has been recorded in the lower South Island and now the upper North Island, which suggests a large geographical spread. Why would we not suppose these two species could set each other aglow any time they get together?
True, the ‘Crystal Falls’ Mycena may only bioluminesce in certain conditions, but I’ll bet it very often does. I’ll bet the reason it has seldom been seen to do so in recent times – and this is not to suppose early Maori were not aware of the phenomenon – is simply people usually use a torch, if they head into the bush by night at all. Witnessing this subtle, ethereal spectactle requires you to wait patiently in the dark for your eyes to adjust.
If any readers live near a suitable forest track and feel like heading on a little night-time expedition to check for glow-in-the-dark fungi on tree ferns, I’d love to hear reports back.
Let’s find out the spread of this glow-in-the-dark treasure and map it, so New Zealanders will know if they have a luminous forest in their neighbourhood.