Spore dispersal . *・°・。｡ . ･ * ° ゜ﾟ

an illustrated guide to fertile surfaces

As surface-dwellers ourselves, it can be easy to think of the life that happens up here as being the main event, with whatever happens underground just setting the stage for us. But for fungi, that script is flipped. When we find mushrooms along our daily walks, it appears that these lifeforms just popped into existence overnight. In reality, the appearance of mushrooms tells us that its fungus has been there—underfoot, within the tree, betwixt the fallen leaves, whatever the case may be—for some time.

Fungi don’t have to make mushrooms at all, and in fact most do not. A mushroom is a fruiting body—a specialized outgrowth designed to spread spores far and wide. But they’re just one way among many that fungi multiply themselves. Some fungi are single-celled yeasts that reproduce asexually,¹ some are bread molds that can change their own genes,² some live their whole lives inside of plants, hitchhiking their way through seeds.³ Even for mycelium-forming fungi, mushrooms are not a requisite. Theoretically, mycelium is immortal—it could go on growing forever if conditions remained favorable.⁴ Which of course they don’t, but sometimes you get a good stretch of millennia.

That said, sexual reproduction has its perks—evolutionarily speaking, of course. While most spores released by mushrooms are trapped in the boundary layer immediately above the earth and will land close to the parent, the ones which escape and lift into the wind can travel vast, vast distances—half a continent, in some cases.⁵ We breathe in spores with every inhalation, as they pervade every biome on Earth in their search for an ideal substrate.

Cordyceps spores riding on the breeze

In hammering home the point that mushrooms are, at the end of the day, a vehicle for spores, I hope to lay the groundwork for the first and most important lesson of mushroom identification: Look for the fertile surface! I can’t tell you the number of mushroom photos I am asked to ID that are just pictures of circles. And while there is definitely some information to glean from the cap surface of a mushroom, it’s not where the most variation occurs.

The mushrooms gathered on any given foray ID table will represent a wide array of adaptations for spore dispersal. The most common, and so more commonly recognized, would be gills. But if you please, come take a tour of some of the many and splendidly strange options~

Gills, aka lamellae, are thin blades on the underside of the mushroom. They are the most common method of spore dispersal and present amazing variation in form. Make note of the differences in spacing, color and texture of a mushroom’s gills, and how/whether they attach to the stipe. It’s all important!

Pores appear as sponge-like holes on the undersurface of a mushroom, but are in fact the ends the tubes where spores develop and launch from. Sometimes so tiny you need a loupe to see and other times huge, pores have evolved throughout the fungi family tree. Many mushrooms which were originally grouped together taxonomically are now, with the advent of genetic sequencing, understood to be examples of convergent evolution—nature arriving at a similar answer to a question asked many distinct times.

Perhaps this method could be more descriptively called spines, but isn’t “teeth” more fun? As with other fertile surfaces, the presence of teeth does not necessarily mean fungi are related. It is a fairly distinctive fertile surface, and mushrooms with it tend to be easier to identify.

As distinct from teeth which point down (stalactite style), coral mushrooms have spires which point skyward (stalagmite style). Some can be puffy-looking (leading to some confusion with lion’s mane), but in general they resemble ocean corals—sometimes to a shocking degree. The fertile surface of a coral mushroom is usually the branches themselves.

Puffballs use arguably the most dramatic spore-dispersal method of all mushrooms. Rather than a visible fertile surface, they form thick skins to protect an enormous (proportionate to the mushroom) spore mass until it has matured. When the time is right, a hole will develop on the top. Anything from raindrops to a passing animal that disturbs the puffball at this stage will launch a plume of spores into the air, volcano-style. One way to make it past the boundary layer!

Importantly distinct from true gills, the ridges found on the undersurface of chanterelles and their close relatives cannot be cleanly removed from the mushroom. Some are deeply grooved enough to resemble gills, and some are almost entirely smooth.

Cup mushrooms are ascomycetes, meaning they belong to an entirely separate phylum of fungi than those above (which fall into basidiomycetes). Unlike the majority of fungi where the fertile surface occurs on the underside, cup mushrooms produce spores face-up, inside the cup surface. While most are small and unassuming, the oddly-shaped and highly sought-after morel is a sort of modified cup mushroom.

Lastly, sometimes you find a mushroom with a fertile surface that just seems WERID. That’s usually a good time to ask yourself—am I looking at one fungus or two? The lobster, bolete eater, and gill gobbler are all examples of parasitic Hypomyces that transform/deform the fertile surface of their host mushroom, using it as an ideal substrate from which to disperse its own spores.

Now that you can identify the fertile surfaces of most mushrooms you encounter, you’ll be ready for next week’s post all about…spore prints! You can make them for fun, you can make them for art, but most of all you can make them for SCIENCE.

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Ps. The images in this post are groundwork for a resource I am making in preparation for my forthcoming picture book On a Mushroom Day. The captions in the final version will be oriented toward kids and families. If you have feedback/questions that arise after reading, I’d love to hear!

1. https://bio.libretexts.org/Bookshelves/Microbiology/Microbiology_(Kaiser)/Unit_4%3A_Eukaryotic_Microorganisms_and_Viruses/08%3A_Fungi/8.2%3A_Yeasts

2. https://www.sciencedaily.com/releases/2020/06/200622133041.htm#:~:text=FULL%20STORY-,Whilst%20most%20organisms%20try%20to%20stop%20their%20DNA%20from%20mutating,mutate%20all%20of%20the%20time.

3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4020682/#:~:text=To%20date%2C%20it%20has%20been,species%20(Centaurea%20cyanus%2C%20C.

4. https://www.britannica.com/science/fungus/Growth

5. https://www.usu.edu/herbarium/education/fun-facts-about-fungi/dispersal#:~:text=Once%20spores%20are%20caught%20by,2000%20km)%20by%20the%20wind.