Seven year wait for a fungus

On 6th November 2009, while I was at Dundreggan, I discovered a large fungus fruiting at the base of an oak tree (Quercus petraea) that I’d never seen before. Situated right at the base of the tree, where the trunk emerges from the ground, it was very large for a fungus, and it had quite a complex shape, with a considerable number of overlapping and interconnected caps. As always when I find something new, I got quite excited and spent a while with the fungus, studying it and photographing it from different angles.

Unfortunately, the fungus had passed its best when I found it, and it was already starting to decay and disintegrate. Nevertheless I took some samples from it to send to Liz Holden, the mycologist who helps me with fungal identifications.

 

 

 

 

 

 

When Liz received the samples a few days later she said they were too far decomposed for her to be able to make a positive identification of what species it was. She listed two or three possibilities, one of them relatively rare, but her suspicion was that it was most likely a commoner fungus called hen of the woods (Grifola frondosa). When I got her message I felt rather deflated, as I’d been hoping that since it was such a distinctive species it would be comparatively easy to put a scientific name to it.

Each year since then I’ve checked that oak tree in late October or early November, to see if the fungus fruited again, but there was never any sign of it at all. Then, on 9th November this year, while I was at Dundreggan to be interviewed by a student from London for a documentary film project about rewilding that she was doing for her degree course, I had a few minutes to spare, so I went and had a look at the tree.

To my surprise and delight, the fungus was there again, in exactly the same place I’d seen it in 2009! While it was wonderful to find it again, my enthusiasm was dampened by the fact that it seemed to be even more past its best than when I’d seen it in 2009. I suspected that it would be difficult to get some material to Liz in good enough condition for her to provide a confirmed identification for what species it was.

I thought that if only I’d checked the tree the previous week when I was at Dundreggan, I might have observed it in prime condition, when the fruiting body was fresh! Nevertheless, I was excited to see it again and I went to find Doug, our Operations Manager at Dundreggan, to show it to him – like me, he has a keen interest in the biological diversity on our estate there. A few minutes later, when we reached the tree and I showed the fungus to him, Doug asked if I’d checked any of the other nearby oaks to see if they had the fungus as well.

In fact I had checked one tree nearby, but there were three others I hadn’t looked at, so we went to have a look at those. Remarkably, at the first one, about 10 metres further up the small burn, I spotted another of these fungi, at the base of the oak, and in almost exactly the same relative position, on the north side of the tree. This one was in much better condition, looking very fresh and as though the fruiting body had just newly emerged from the tree.

This discovery really made my day! It was the opportunity I’d been waiting 7 years for, and somehow it made me think of the title of an old Marilyn Monroe film, ‘The Seven Year Itch’. The mystery of what it was had been itching away in my mind since 2009! I knew that I’d be able to get the species identified now, and I also set about taking more photographs of it, from a variety of different angles and positions.

 

 

 

 

 

 

 

 

 

 

 

Because this fungus was in good condition, I was able to get a close look at the structure of it, which was somewhat like that of a head of cauliflower. Underneath the individual caps, or ‘fronds’ as they looked like, were stems that branched off a central larger stem, in very much the same way as a cauliflower is formed. This struck me as both quite unusual (I’d never seen this in a fungus before) and very distinctive. So much so, that when I got home that evening and could check my fungal references, I was quite sure that it was indeed the fungus that Liz had suspected it to be, back in 2009 – the ‘hen of the woods’ (Grifola frondosa). The specific name ‘frondosa’ is a real giveaway about this, as it shows that the frond-like nature of the caps of the fruiting body is a distinctive enough feature to warrant including it in the scientific name for the species. This identification was also confirmed by Liz, when I emailed the photos to her – she didn’t even need to see the physical samples to be certain of it.

While I was photographing the fungus, I took some images of the underside of the caps. Unlike many fungi, which have gills on their undersides, the hen of the woods has tube-like structures called pores that are packed closely together and these release the spores that the fungus uses for reproduction.

 

 

 

 

 

 

In my email exchange with Liz, I asked her about the fact that it had been 7 years between fruiting periods for this fungus, wondering if there was a significance to this. She replied that she doesn’t know so much about saprotrophic fungi (those which live on, and break down, dead wood or other plant material), of which this is one.

She referred me instead to Lynne Boddy, an expert on fungi who is based at Cardiff University. When I contacted her, Lynne explained that because of the size of its fruiting body this species must require a substantial amount of nitrogen to produce it, and it likely takes a number of years for the fungus to accumulate the resources for this. This makes a lot of sense to me, as I imagine the fungus is quite slow in breaking down the heartwood of the oak, converting the tough cellulose and lignin there into the chitin that forms the cell walls of the hyphae – the thread-like structures that are the main body of the fungus. For those filamentous structures within the trunk of the tree to then give rise to this massive fruiting body seems little short of miraculous to me! It must be a huge effort on the part of the fungus to pump out all the accumulated material and form the fruiting body in such a short period of time …

It’s quite remarkable to think that those tiny hyphal filaments can produce such a complex and beautiful fruiting body, which has an immense surface area, arising from its fractal morphology. It’s a true work of Nature’s art, and I imagine that each fruiting body is unique – as individual and different as every snowflake is to all others. I was also struck by the fact that on the two different oak trees, the fungi were fruiting at exactly the same place, in terms of their locations – on the north side of the trees, at the base of their trunks. I wondered if there was any significance to this, but when I asked Liz about it, she replied stating that she thought it was just by chance that they were oriented in the same aspect, as she’d seen the fungus in various different orientations on trees.

What did seem quite interesting to me though was that the fungus was fruiting at the same time on these two different trees. Given that one of them hadn’t fruited for 7 years (and I don’t know how long it was since the fresher specimen had last fruited), I wondered at the fact that they were synchronised now? With fungi that live in soil, it’s understandable that fruiting can be synchronised, as the hyphae may well be connected underground, and they all experience the same conditions of soil moisture content, rainfall etc.

However, for a saprotrophic fungus like Grifola frondosa, where its main body, the mycelium, which is composed of the hyphae, is inside an individual tree, I’m guessing that the fungus in one tree has no direct contact with the fungus in another. However, scientists in several countries have shown that individual trees can be connected through their roots underground being linked by the mycorrhizal fungi that exchange nutrients with them. Chemical signals appear to be passed through this ‘Undernet’, and this enables trees to communicate with each other about, for instance, insect infestations and the need to utilise chemical defences to counter them. Perhaps the chemical balances in these oak trees are similarly communicated from one to another, and the saprotrophic fungi are clued in to this, and can thereby synchronise their fruiting?

This is obviously speculation on my part, but I suspect that there is some still unknown factor at work that will explain why these fungi in two different trees have fruited at the same time, when their fruiting periods are seemingly so many years apart. Irrespective of that, the discovery of this fungus fruiting at the base of the two oaks renewed and deepened my sense of wonder, both at Nature in general, and at the fungal kingdom in particular. Fungi are generally under-appreciated by most people, but they do produce some of the most beautiful, albeit ephemeral, organic structures in our forests and other ecosystems, and I felt privileged to have spent time with these ones on this day.