Back in March a small group of us cycled along the Forest Way to look at the pond near Hartfield (TQ47163599). It was rather cold and not the most species-rich outing we have had. However, with such meagre pickings we ended up looking very closely at small things growing on the willows. In addition to the moss Orthotrichum affine and some tiny invertebrates (spiders, mites etc), we found a very small orange-red fungus which I photographed before we froze and headed home.
Showing the picture to expert mycologist Nick Aplin of the Sussex Fungi Group, unsurprisingly he asked for a sample, so I re-visited the site and collected some on 30 March. At the same time I noticed some black marks on dead willow twigs, and collected a few of those for him as well.
Nick noted that the small orange-red fungus was in the family Nectriaceae, but he needed to do some work on it. A few days later he reported the following:
The visible orange patches breaking through the bark is the asexual stage which produces long, Fusarium-like conidia.
For identification of Nectriaceae species, we need to see the sexual stage (teleomorph) too, so I put your collection into a moist chamber for a day or two to try to culture it. A few perithecia formed, but they are immature at the moment and don’t contain any sexual spores (ascospores).
However, I was able to test the reaction to Potassium Hydroxide of the perithecia, which was violet (positive), narrowing it down to half a dozen or so genera.
A few weeks later Nick contacted me again to add further news about the identity of the fungus:
It’s Fusarium coccophila. I came to this ID after realising the fungus is not growing from the bark, but from dead scale insects, Chionaspis salicis.
The sexual stage never matured in your collection… F. coccophila has only three previous UK records (none from Sussex)
Nick also sent his photographs showing the results of the microscopy:
In your collection there were in fact a few free ascospores (you can see a blurry one above the ‘r’ in ‘colour’ in the photo) that fit within the measurements of those quoted in an article from Studies in Mycology.
I see that Seifert et al propose the name Microcera coccophila (I suppose for the holomorph) which is what we should probably be calling it, but the taxonomy here is as complicated as it gets, plus the British Database still has it under Fusarium.
So, it was a fungus (Fusarium coccophila aka Microcera coccophila) that grows on dead insects, and a new county record! As the distribution map shows, the other records in the UK all appear to be in Wales. One of the English names for its host Chionaspis salicis is Black Willow Bark Louse, which can be a pest on a number of plants. A series of early twentieth century drawings of this bug is available at the Royal Society Picture Library.
That is all rather exciting, but what of the black fungus on the willow twigs?
Nick’s first response was extremely tantalising:
Your second species is very interesting -It should be a Cryptodiaporthe (though some authors prefer the name Plagiostoma).
I’m familiar with the two species commonly found on Willow (the only two ever recorded on the substrate in the UK – C. salicina and C. salicella), but yours doesn’t fit either.
I ran your species through a recent (2011) study on the group (which includes species from the US and a few new European ones) but had no luck there either!
The only hint I can find as to the identity of your species is a post on Ascofrance. The data fit your specimen exactly.
However, Nick also noted that that report did not end up with the species being determined, and it is plausible that it could be a hitherto-undescribed species. I’d only collected a small amount, so to do further investigations Nick needed some more material, whereupon I went back on 7 April and collected many more similar-looking small twigs.
Last week Nick got back to me:
I’ve searched the material on Willow branches but that Plagiostoma hasn’t turned up. I’m keeping the collection in moist culture in the hope that something might happen eventually. I did find Plagiostoma salicina, though.
I also attach a collage of Plagiostoma (=Cryptodiaporthe) salicina which I found on your willow branches (the macro part top-left is not from your material but the rest of it is).
The micro parts are to the same scale as my earlier collage of the other, possibly unknown Plagiostoma (=Cryptodiaporthe). The differences are subtle but can easily be made out when the images are put side by side.
So, the similar-looking black fungus on the willow twigs that I collected on the last visit turned out to be a common species (Plagiostoma salicina aka Cryptodiaporthe salicina), yet there is a reasonable likelihood that the first sample is something much more unusual. Even so, the ‘common’ species is in fact a first county record for East Sussex. I can sense that more visits to the pond near Hartfield may well be necessary.
This turns out to be a remarkably good reward for what was otherwise a somewhat disappointing day out for wildlife. Is it that noteworthy, though? Of all the groups of organisms in the UK, there are more known species of fungi (c 12000) than anything else, including flies (c 7000) and beetles (c 4000). Within the fungi, the Ascomycota, which includes the species in this article, may amount to at least 5600 species, yet, because they are small and require microscopical examination to determine them, there are undoubtedly a huge number of species yet to be described for the first time. Even many known species are significantly under-recorded, simply because they are easily over-looked, and there are insufficient experts able to identify these small organisms. If you have some willow in your garden there is a reasonable possibility that it may be host to these or other micro-fungi.
Careful, attentive looking at even the most familiar places can certainly turn up novel discoveries. Just because something looks small and uninteresting doesn’t mean that it is!
Huge thanks to Nick Aplin for his investigations, determinations and photographs.
 Gräfenhan, T., H.-J. Schroers, H.I. Nirenberg and K.A. Seifert. ‘An overview of the taxonomy, phylogeny, and typification of nectriaceous fungi in Cosmospora, Acremonium, Fusarium, Stilbella, and Volutella.’ Studies in Mycology, 68 (2011): 79–113. doi:10.3114/sim.2011.68.04, available at: <http://www.cbs.knaw.nl/publications/Sim68/09_An%20overview%20of%20the%20taxonomy,%20phylogeny,%20and%20typification%20of%20 nectriaceous%20fungi%20in%20Cosmospora_Acremonium_Fusarium_Stilbella_and%20Volutella.pdf>. See especially pp. 104-106.
 Watson, G.W. ‘Chionaspis salicis.’ Arthropods of Economic Importance: Diaspididae of the World. Web. <http://wbd.etibioinformatics.nl/bis/diaspididae.php?selected=beschrijving&menuentry=soorten&id=100#>
 Marren, Peter. Mushrooms. Gillingham: British Wildlife Publishing, 2012.