Macrocybe crassa: A giant mystery solved?


Probably Macrocybe crassa

I first found these mushrooms a few years back, a whole bunch of these fricken enormous clumps of mushrooms appeared in my neighbors pile of compost. Having never seen anything even close to these giant clumps before I was impressed and excited by the find but unable to get an ID that I was happy with, in my field guide the only genus that looked close was lylophyllum. Every year since they have fruited again over summer in the same spot, I would stop and admire them, take a few photos, take a few home, one time I even fried a few slices up just for a taste. They tasted pretty good but I spat them out unwilling to swallow a mushroom that I wasn’t able to ID.


The second location I found Macrocybe crassa

Earlier this year (2017) we were driving around near Coramba and my partner said she saw some kinda big white mushroom, I turned around and found the second patch of these giants, they were growing from piles of soil mixed with gravel and organic matter that had been dumped by the road crew. Some of the clumps were rotten, others just emerging from the soil, over the back I found some with caps over 200 mm across standing over 300 mm above the ground, the biggest mushrooms I’ve ever seen. Not long after this I saw a post on the internet, local legend Darcey Browning from Darkwood had found his own patch and true to form, went straight to the press. He wasn’t having much luck IDing them either.


Macrocybe crassa

Finally the other day I emailed my pictures to the Queensland mycological society and got a prompt reply from one of the head honchos, he said that he was 95 percent sure that they are Macrycybe crassa, and that he has found them in his own yard further north. Macrocybe crassa are eaten in some parts of Asia, most of the pictures and info I have found so far are from Thailand. There have also been a few attempts to cultivate them. Where to now with these novel giants? First i will send away a sample for dna analysis and if it comes back as Macrocybe crassa I will have a bit more of a taste next time I cross paths with these noble giants. I’m also keen to clone them and see if they can be domesticated. Stay tuned. To see my other m. crassa shots click here.

Update: My dna results are back for these guys, the sequence came back as a 99 percent match for Macrocybe gigantea, an edible species known from India and Pakistan where work has been done on cultivation of these fungi. Something of note with the genus macrocybe is that they can contain cyanide! Some sources say this can be cooked out while others say this is only partially true! Read more here and here.

Australian Macrocybe gigantea

M. gigantea from this season, same location as last year but the caps are darker in colour

I have just found some more fresh mushrooms this season, they are much darker this year, the caps are mocha in colour! Its interesting because in the same patch last year they were pale cream to white. Anyway finding some fresh ones has got me interested in cooking some but first I decided to look into this cyanide thing. I am by no means qualified to make any assessments about the toxicity of these fungi so I will just compile the facts from my research here in one place. In this study done in Japan Cyanide was tested for in 54 different types of fungi and at the top of the list, with by far the highest quantity was Tricholoma giganteum (macrocybe gigantea) at the level of 0.086-0.283 milligrams per gram. To give an idea the next highest was Grifola frondosa at 0.0018-0.046 mg/g. To compare with another source of cyanide, amygdalin found in apple seeds. One gram of finely crushed or chewed apple seeds may deliver up to 0.06-0.24 mg of cyanide, roughly the same amount as the m. gigantea. The above Japanese study also sought the type of cyanide which turned out to be free cyanide. The term free cyanide refers to the cyanide ion and hydrogen cyanide. Hydrogen cyanide is a colorless, extremely poisonous liquid that boils slightly above room temperature at 26°C. Hydrogen Cyanide has a faint, bitter, almond-like odor which I believe I can smell in the mushrooms. Hydrogen cyanide is considered one of the most hazardous forms of cyanide. While some say that the cyanide is removed by cooking the Japanese study concluded that the remaining percentage of the cyanide in T. giganteum after grilling for 6 minutes was 65%, while that after boiling for 3 minutes was 46% (27% in basidiomycetes (the fungi) and 19% in broth). The level of residual cyanide in T. giganteum after cooking might be sufficient to cause poisoning with symptoms such as vomiting. This is backed up by at least one case of non fatal poisoning from Macrocybe spectabilis in Hawaii. The reality is that the tiny quantity of Cyanide in the mushrooms and the fact that it is reduced by fifty percent in cooking shows that its highly unlikely to cause serious poisoning unless a very large quantity of poorly cooked mushrooms are eaten. For an 81 kg adult to become seriously ill, they would need to eat about 41-286 mg of cyanide. Thats between 350g and 9kg of mushroom! Still until more is known about this fungi is probably better not to eat it at all or if you do eat it, boil for at least 3 minutes before draining and frying and only eat a small amount.



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