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Polypore Fungi

It’s unlikely that you first think of a polypore when hearing the word “mushroom”. Let’s get some of the terminology out of the way to better understand the distinctions between organism parts and types that will be discussed in this article. Polypores (fig. 1) are a group of fungi that form bracket or shelf-like fruiting bodies, with pores or tubes on their hymenium (fig. 2) [1]. These fruiting bodies are the mushrooms and contain fungal spores. Prior to producing a mushroom, fungi live as mycelium (fig. 3) within their substrate. Mycelium is a collection of branching, tubular filaments of the fungi [2]. Think of it this way: mycelium is to a cherry tree, as a mushroom is to a cherry. The mycelium will grow until the fungus needs to reproduce, at which point a mushroom will be grown to ultimately spread its spores. Much in the same way as a cherry tree will grow until it needs to reproduce, at which point a cherry will be grown to ultimately spread its seeds.

(fig. 1) Turkey Tail Polypore (Trametes versicolor)

(fig. 2) Fungal Hymenium

(fig. 3) Fungal Mycelium

Most species of polypores are saprobic, meaning they are decomposers of dead organic material [3]. However, there are also polypore fungi that are parasitic (decompose living organic material) and mycorrhizae (form a symbiotic relationship with plants). This article will primarily focus on the origin story of the quintessential saprobic polypore. The first stop along this nearly 500 million year long origin story comes when a little class of complex organic polymers called lignin first emerged in plants. Lignin is the key component of wood and bark that provides its strength and rigidity. Lignin evolved simultaneously with the rise of vascular plants on Earth ~450 million years ago and led to the strengthening of vascular tissues as well as the creation of a physical and chemical defense against co-evolving animals and microbes [4]. To put simply, this new, woody scaffolding allowed plants to quickly grow to unprecedented sizes and develop a nearly impervious shield against decay and predation. The evolutionary development of lignin ultimately led to vascular plant dominance over Earth’s surface.

The second stop along this story brings us back to saprobic fungi. As previously mentioned, “saprobic” refers to a fungi’s ability to decompose dead, organic material. However, lignin's physical and chemical defenses were so great that a proposed 150 million years separated the emergence of lignin and that of white rot. White rot was the first fungi capable of using its enzymes to break down lignin’s powerful chemical bonds [5]. This part of the story takes us from ~450 to ~300 mya, but only outlines the origin of the saprobic nature of white rot fungus. White rot was capable of breaking down lignin, but was still incapable of producing the polypore mushroom 300 mya. Rather than using a fruiting body to disperse fungal spores, they had free-swimming uniflagellate zoospores that required moist conditions or direct contact with animals to spread [6].

(Side note & breather: for a frame of reference, dinosaurs began walking the Earth approximately 245 million years ago. Our story today began over two hundred million years before dinosaurs.)

So we’re at 300 mya with white rot fungus finally being able to break down lignin, but unable to produce a mushroom. It took at least another 155 million years until fungi formed the first fruiting body. As stated in an article from the The American Journal of Botany, the minimum age estimate for the first recorded homobasidiomycetes (mushroom-forming fungi) is the mid-Cretaceous period (145.5 - 66 million years ago). The mushroom that was formed by this fungus? A bracket fungus, a.k.a. polypore [7]. Finally, we have the complete origin story of our main character, the saprobic polypore.

Mossy Maze (Cerrena unicolor)

Artist’s Bracket (Ganoderma applanatum)

Why should we care about this story and polypores at all? Well, the first part of my answer to that question is that origin stories are cool, mushrooms are cool, and therefore mushroom origin stories are double cool. The second part of my answer is that these fungi have directly impacted not only the landscape of vascular plants on our planet, but have shaped our human existence as well. A 5000+ year old Neolithic corpse, commonly referred to as the “Iceman”, was found preserved in an alpine glacier in 1991. Along with additional equipment, the Iceman had with him three fungal objects: two pieces of a polypore mushroom (fig. 4-5) and tinder material (fig. 6) made from a different polypore mushroom [8]. While the tinder material made from the Fomes fomentarius, or true tinder polypore, speaks for itself, the other polypore mushroom pieces were believed to be used by the Iceman as medicinal supplements. The Piptoporus betulinus, or the Birch Polypore, is believed to be used by the Iceman for its antibacterial and antiparasitic properties.

(fig. 4-6) The two Piptoporus betulinus fragments that are mounted on a leather thong and the Iceman’s girdle bag and it’s fire-starting contents featuring a clump of the Fomes fomentarius. (Photographs produced and owned by Römisch-Germanisches Zentralmuseum, Mainz, Germany)

This fungi is now well known for these medicinal properties as well as its anticancer activities [9]. From penicillin that fights bacterial infections, to lovastatin that lowers cholesterol, and even cyclosporine that enables human organ transplants, fungi are responsible for some of the most important medicines in human existence [10]. As evident from the Iceman, humans have depended on nature for their basic needs, including medicines, since the earliest civilizations. Natural products today are responsible for over one-third of the approved drugs on the market [11]. The plants and fungi these medicines are derived from, as well as the environment they grow in, face an unprecedented threat by the same creatures that have used them to save their own lives. 10 million hectacres of forest, an area nearly the size of Germany, is lost every year by deforestation [12]. There are over a 1000 species of polypores that have been discovered, but there is an incredible amount of diversity still unknown even in well-researched landscapes. Even with the intention of reforestation, the current rate of old growth forest loss will inflict unimaginable damage and loss of species. It seems like a generally good idea for the planet, and selfishly for human existence, to stop the mass destruction of the very ecosystems that is giving us over a third our medicine. Although the thought of standing up against deforestation on this scale can seem daunting, there are steps that you can take in your own life to help. Planting a tree, using less paper, buying sustainable wood products, and doing your own research are just a few ways you can make a difference.

Here are a few resources that might help kickstart your support: 

There is far more to learn about these beautifully intricate organism, but I hope this article helps sparks interest in and passion for the world around us. Oh, and see if you can make someone smile today (even if that “someone” is you).

-Noah

References & Acknowledgements:

  1. Plantbiology.natsci.msu.edu. (n.d.)., https://plantbiology.natsci.msu.edu/mushrooms/polypores/

  2. Encyclopædia Britannica, inc. (n.d.). Mycelium. Encyclopædia Britannica., https://www.britannica.com/science/mycelium

  3. Runnel, K., Miettinen, O., & Lõhmus, A. (2021, January 18). Polypore fungi as a flagship group to indicate changes in biodiversity – a test case from Estonia - Ima fungus. BioMed Central., https://imafungus.biomedcentral.com/articles/10.1186/s43008-020-00050-y

  4. Renault, H., Werck-Reichhart, D., & Weng, J.-K. (2018, November 13). Harnessing lignin evolution for biotechnological applications. Current Opinion in Biotechnology., https://www.sciencedirect.com/science/article/pii/S0958166918300636#:~:text=It%20is%20thought%20that%20the,dominance%20of%20the%20terrestrial%20ecosystems

  5. Behind the scenes: How fungi make nutrients available to the world. Energy.gov. (n.d.)., https://www.energy.gov/science/articles/behind-scenes-how-fungi-make-nutrients-available-world#:~:text=Although%20fungi%20appeared%20millions%20of,type%20to%20break%20down%20lignin

  6. Laundon, D., Chrismas, N., Bird, K., Thomas, S., Mock, T., & Cunliffe, M. (2022, March 1). A cellular and Molecular Atlas reveals the basis of chytrid development. eLife., https://elifesciences.org/articles/73933

  7. Hibbett, D. S., Donoghue, M. J., & Tomlinson, P. B. (n.d.). (rep.). Is Phellinites digiustoi the Oldest Homobasidiomeycete? (Vol. 48, Ser. 7). Botanical Society of America.

  8. The Iceman's Fungi - researchgate. (n.d.)., https://www.researchgate.net/publication/222280519_The_Iceman's_fungi

  9. Pleszczyńska, M., Wiater, A., Siwulski, M., Lemieszek, M. K., Kunaszewska, J., Kaczor, J., Rzeski, W., Janusz, G., & Szczodrak, J. (2016, September). Cultivation and utility of piptoporus betulinus fruiting bodies as a source of anticancer agents. World journal of microbiology & biotechnology., https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4963449/

  10. McHale, E. (2022, June 30). Secret fungi in Everyday Life., https://www.kew.org/read-and-watch/everyday-fungi-food-medicine#:~:text=Penicillin%2C%20which%20fights%20bacterial%20infection,Aspergillus%20terreus%20(lowers%20cholesterol)

  11. Cao, S., & Kingston, D. G. I. (2009, August 1). Biodiversity Conservation and Drug Discovery: Can they be combined? the Suriname and Madagascar experiences. Pharmaceutical biology., https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2746688/

  12. Ritchie, H., & Roser, M. (2021, February 9). Deforestation and forest loss. Our World in Data., https://ourworldindata.org/deforestation#:~:text=Globally%20we%20deforest%20around%20ten%20million%20hectares%20of%20forest%20every%20year

All photographs are taken and owned by Noah Hilton unless otherwise stated.