Easily one of my favorite fungal finds around this time of year is actually quite a common species, especially if you live around deciduous forests. The saprophytic fungus, Panellus serotinus, also known as the late fall oyster isn’t actually an oyster mushroom at all. Unlike the fungus featured in a Fungi Friday from two weeks ago, Hohenbuehelia mastrucata, Panellus serotinus is not from the oyster family (Pleurotaceae). Though, it is still highly regarded in Japan as a delicious edible species.
This species has a huge distribution and can be found in most habitats in northern latitudes with mixed deciduous forests. Panellus serotinus fruits from several species of dead broadleaf trees and every time I have found it, it has been grouped in clusters of five or more caps. What’s most attractive to me is its color variations. You can’t identify it by looking for just one color, because this species produces some caps that are not only yellow, but olive green, brown, and sometimes a mixture of all three. I have even seen pictures of this mushroom with grey-purple hues so you really have to look at other distinguishing features for positive identification. Even two fruiting bodies growing inches away from each other can produce strikingly different colors.
Yellow and olive green individuals growing inches from each other.
The bottom of the mushroom is a light yellowish tan, and when the stem is present, it’s actually pretty large compared to the overall medium-small stature of the fungus. The time of the season can also point you in the right direction for proper identification. Its common name as well as its species name serotinus, which also means late, signifies when this species actually fruits. Sadly, when it does appear, you come to the depressing realization that the mushroom season has come, and is nearly gone. Even still, I’m oddly optimistic because in my region, we had such a warm, almost summer-like beginning to autumn, that I believe there are still many species to be found.
Comparatively large stem and and yellow-tan underside of Panellus serotinus.
In North America, this species is not sought after by most foragers. It produces a mucous layer on its cap, that makes it a bit slimy. This gelatinous layer may be a mechanism that evolved to reduce water loss, or a mechanism that deters mycophagous insects and slugs. The relative abundance of water during this time of year make me think the slimy caps function to be the latter, but additionally, it could act as an agent to enhance its frost tolerance. A chemical analysis still needs to be conducted on its mucous layer to confidently conclude its exact function. Its sliminess may deter invertebrates, but in no way, shape or form deters mycophagous Japanese foragers.
This species mucous layer is better observed when wet. Photo by Walt Sturgeon.
Like I said in the beginning of this post, this fungus is highly regarded as a choice edible in Japanese culture. Its Japanese common name is the Mukitake. Several studies in the past decade have looked into the secondary compounds this species produces, and some promising results have turned up. In 2010, Nagao K and his team analyzed the livers of two groups of mice with nonalcoholic fatty liver disease (NAFLD). One group of mice was fed with Panellus serotinus, while the other group acted as the control. In short, after four weeks of feeding, the group that was fed Mukitake had markedly healthier livers. Lipolytic enzyme activity in these mice where enhanced while lipogenic enzymes accioated with fatty livers where reduced in Mukitake fed mice. These fungi may boost human health, but depending on where these fungi are found, they could be dangerous too.
The 2011 debacle involving an earthquake, a tsunami and the Fukushima Daiichi nuclear power plant resulted in huge radioactive plumes being released from the plants reactors. Once the emergency generators that powered the cooling systems failed, three nuclear meltdowns ensued. Large quantities of radioactive material were released into the surrounding environment, and to this day we are still seeing the environmental tribulations.
Deposition of radioactive cesium after the Fukushima nuclear meltdown. From Toshihiro Yamada 2013.
In 2013, Toshihiro Yamada put together a review paper, showing the apparent radioactive contamination of fungi growing in Japan. Some of these data are rather alarming. Just six months after the incident, several species of mushrooms in six different locations surrounding the meltdown were collected and their radioactivity was analyzed. One of the most contaminated mushrooms was (you guessed it) Panellus serotinus.
Just six months after the disaster, Panellus serotinus collected in Japan had elevated concentrations of radiocesium. Toshihiro Yamada 2013.
These findings are disturbing because the saprotrophic fungi analyzed grew from trees that were long dead before the nuclear mishap. In hundreds of years, think of all the radiocesium trees will sequester and store in their lignin rich wood. How high will the levels of radiocesium within Panellus serotinus be that fruit from radioactive trees? Let’s just say that Japanese mushroom enthusiasts should probably import Panellus serotinus from uncontaminated areas if they want to enjoy them in dishes or treat liver disease. The forest floor bears fruit for us to enjoy, but it can be contaminated and ruined in an instant.