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Wooly Velvet Polypore - Onnia tomentosa

Good evening, friends,

This time of the year the offices of Mushroom Monday are very busy sorting through the dozens of Mushroom Monday candidates to select just one each week. This week we’ll lean on recency bias and look at the last mushroom identified yesterday afternoon at the Friends of Fungi retreat. The Woolly Velvet Polypore (Onnia tomentosa) was found next to two stately conifers (one pine and one spruce) and didn’t make for the easiest of identifications. The specific species isn’t certain without looking at the specimen through a microscope, but we can always learn more about what this fungus is doing in the ecosystem and take a peak at some other fun finds from the weekend too.

Onnia tomentosa

Fun Facts

A study out of British Columbia found that O. tomentosa possesses essential fatty acids which have potential medicinal applications (Reference 2). The study determined that ethanol extracts of the mushroom possessed high antiproliferative activity against human cervical cancer cells (in a lab setting) and a water extract of the fungus had weaker immunomodulatory properties. It was noted that the fatty acids (predominantly linoleic and oleic acids) actually stimulated growth of cancer cells in other studies. The effect the fatty acids have on cancer growth seems to be dependent on the type of fatty acids and the type of cancer.

Onnia tomentosa
The lightish brown pore surface bruised a dark brown pretty quickly after touching it.

The genus name Onnia was introduced by Finnish mycologist Petter Adolf Karsten in the late 1800s who named the genus after his son, Onni. The epithet tomentosa is common in scientific names and means “thickly and evenly covered with hair”. A proper description for the cap of this mushroom.

Onnia tomentosa
The tomentose cap in question.

The fungus is considered a pathogen on conifer plantations in British Columbia, where most of the scientific research on this species has been conducted. A different, earlier study noted that the fungus was able to move from tree to tree when the roots of the trees connected, "but cannot extend more than a few centimetres outside the roots” (Reference 3). It’s possible that this fungus was growing on both the pine and spruce roots where we found it.

Onnia tomentosa
Fruiting bodies popping up from the underground roots of the tree.


Similar species are abundant. Our first quandary when trying to identify this mushroom was whether this was the Dyer’s polypore (Phaeolus schweinitzii) or whether this was actually Onnia tomentosa. There was some flipping and flopping but in the end we used Potassium Hydroxide (KOH - potassium is K and the OH is an Oxygen atom bonded to a Hydrogen atom, creating hydroxide). O. tomentosa first turns red in KOH before quickly turning black, while P. schweinitzii turns black as well (but with a red intermediate stage). As if we weren’t already confused. Regardless, it came down to a bit of a gut feel but the colors, texture, bruising, and KOH aligned more with O. tomentosa. Now to determine that this was O. tomentosa rather than a different species of Onnia (like O. leporina or O. subtriqueta) we would’ve needed a microscope, but at that point I was tired and wanted to go home.

Onnia tomentosa
Liquid drops of KOH looking reddish on the margin of the cap before fading to black.

When the identity is uncertain, it’s still good to understand (or think you understand) what the fungus is doing in the environment. As previously noted, the fungus is saprobic on the roots of conifers, particularly spruce and pine trees. The fungus grows throughout boreal and sub-boreal forests of the northern hemisphere, but it’s possible that different species inhabit different continents and O. tomentosa is North America’s species. The mushrooms grow during mid to late summer and can pop up solitarily or gregariously above the roots they are digesting.

Onnia tomentosa
The stringy inside had a brownish, turmeric color.

Friends of Fungi

We had another enriching Friends of Fungi weekend up at Menla. Here are a few of my favorite fungal finds from the weekend, and all mushrooms I had never found before:

Cat’s Tongue (Pseudohydnellum gelatinosum). Most jelly fungi are gelatinous blobs but those spines on the underside of this mushroom lead to an instant identification. This mushroom can be consumed raw but there wasn’t too much flavor in the part I nibbled, and the texture is how it looks - like gelatin.

Pseudohydnellum gelatinosum

Blue Mycena (Mycena subcaerulea):

Mycena subcaerulea

Entoloma violaceum (which is a scientifically invalid name so it actually looks like this species still needs to be formally sequenced and described):

Entoloma violaceum

Not mush rest for the wicked as this Thursday I’ll head to the Northeast Mycological Federation annual foray taking place this year in Kerhonkson, NY.

Will hopefully have more colorful mushrooms for show and tell next week,



1) Kuo, M. (2022, February). Onnia tomentosa. Retrieved from the MushroomExpert.Com Web site:

2) Lee HX, Li WM, Khatra J, Xia Z, Sannikov O, Ling Y, Zhu H, Lee CH. Antiproliferative Fatty Acids Isolated from the Polypore Fungus Onnia tomentosa. J Fungi (Basel). 2022 Nov 3;8(11):1163. doi: 10.3390/jof8111163. PMID: 36354930; PMCID: PMC9693168.

3) Germain H, Bergeron MJ, Bernier L, Laflamme G, Hamelin RC. Patterns of colonization and spread in the fungal spruce pathogen Onnia tomentosa. Mol Ecol. 2009 Nov;18(21):4422-33. doi: 10.1111/j.1365-294X.2009.04370.x. Epub 2009 Oct 5. PMID: 19804376.


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