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Danny’s DNA Discoveries – Russula
by Danny Miller
These mushrooms can go through quite a transformation. One member from Japan, Russula subnigricans, is deadly poisonous and its close relative that grows in California, Russula cantharellicula, may also be poisonous, so we do not eat any of these, just in case, even though none of the ones that grow here have been proven to be poisonous.
Russula nigricans, probably our most common clade member, can get quite large (20cm), has gills spaced the most widely apart, turns distinctly red when damaged and then very black and has a dry cap. On the east coast they have the related species R. dissimulans, but although some have thought our species looks more like that than the European R. nigricans, our more than half dozen specimens tested so far are all proving to be R. nigricans. It seems to associate with many different trees in Europe so maybe that’s why it was able to migrate over here successfully, where it is commonly found with Doug fir and hemlock, even though those are different genera than the conifers found over there. Many of the species in this clade seem to associate with Doug fir and hemlock over here.
Russula nigricans starts out completely white, turns red where damaged and eventually, completely pitch black – Photos © Ben Woo and Danny Miller
Proving the existence of this species in the PNW has brought up some interesting concepts and challenges. In the main introduction, I mentioned that mushrooms are diploid, like humans, meaning there are two complete sets of DNA inside the chromosomes, one from each parent, that combine to help create the features of the organism. Those two sets of DNA have differences, so the sequence of a mushroom has locations where there are two possible nucleotides. At first, our local specimens were seen to have different DNA sequences than those from Sweden, near the “home” location of the species, in half a dozen places, plenty enough difference to suggest ours was not the same species. But a closer look found a “missing link” sequence from Sweden, that managed to amplify both DNA strands showing both possibilities. Other Swedish sequences had happened to amplify one of the “alleles”, and our PNW sequences had happened to amplify the other “allele”, so the sequences were different. But this “missing link” Swedish sequence had both alleles in the sequence (one matching the other Swedish sequences and one matching our local PNW sequences), allowing us to conclude that there were intermediate sequences between our local species and actual Swedish Russula nigricans. Spotting differences in DNA only suggests the possibility that you may have another species, but doesn’t prove it until you study other possible explanations like this one. Noise in the chromatogram is another reason (one sequence has mistakes in it that aren’t the real nucleotides). Careful analysis of each DNA nucleotide comparing against many other sequences may be necessary to reach a reliable conclusion.
R. albonigra is also large, goes straight to black without the red, has its gills a little closer together and it may taste of menthol. Our sequences show at least a couple of differences each in ITS1 and ITS2, but for now I will assume that ours is the same species, as has been assumed. It also associates with various trees. Russula atrata is a bit of a mystery. It was described from Oregon near oak and pine (and said to be common down through central California), so it’s definitely one of our local mushrooms, but it may just be an R. albonigra that had an unusually thick cap cuticle (that difference may not be significant enough to mean it’s a different species). If we can ever find it again, we should study it to find out. Please be on the look out! The enzymes that make the Compactae turn black seem to deteriorate the DNA quickly, as it is proving very difficult to sequence ones that have been kept for any length of time, so new material may have to be found to attempt to solve the mysteries of this group.
Probable R. albonigra © Ben Woo
Russula adusta group
Russula adusta group is a not uncommon (as a group) bunch of more regular-sized mushrooms (up to ~10cm) with sticky caps instead of dry caps that may smell of wine barrels. The stem bases may get wrinkly. They go at least a little red before turning grey, but not always as pitch black as the previous two species can. Our studies show that we have three species here. One of them may be the real thing (or is at least close, 1-2 base pair differences in ITS2 but 3-5 differences in ITS1 which may or may not indicate a different species).
Russula aff adusta #1 was found near Victoria, BC with old growth Doug fir and hemlock. I do not yet have a photo.
Russula aff adusta #2 has the same description.
Russula aff adusta #2 © Marty Kranabetter
Russula adusta? (#3) was found at Mt. Rainier at the Dalles under unspecified trees, and is the closest genetic match to the real species. It’s >=1% different, and may or may not be the “real thing” or a third local species.
R. adusta? (#3) © NAMA and the Field Museum of Natural History
Russula acrifolia is the only Compactae species consistently hot tasting, and it turns grey or black perhaps with some red first. Until now it has been assumed that our hot tasting Compactae was Russula densifolia, since some mycologists think that can also be a hot tasting Russula. This indicates that the Europeans should also take a closer look at their species to see if the “real” R. densifolia is mild or hot or possibly both. There are some ITS DNA differences (5-7) between our R. acrifolia and those in Europe, which may or may not mean that it is a unique species, but even European samples have a few DNA differences between them so these could all be the same species. Further studies should determine if the hot taste reliably separates this species from the various Russula adusta species, and what trees it associates with (reports so far are very vague).
Possible R. ‘acrifolia’ © Ben Woo
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