Chapter 5: Kingdom Eumycota: Phylum Basidiomycota

Welcome to Last Minute Lecture.

This free chapter overview is designed to help students review and understand key concepts.

These summaries supplement not replaced the original textbook and may not be redistributed or resold.

For complete coverage, always consult the official text.

Okay, let's unpack this.

Imagine a hidden world,

vast and intricate, supporting entire yet often overlooked.

We're talking about the kingdom of fungi, and today we're taking a deep dive into one of its most diverse and powerful groups,

the basidiomycota.

That's right.

If you've ever spotted, you know, a classic mushroom, a puffball, or even those strange kind of jelly -like growths on wood, you've definitely encountered a basidiomycate.

And our mission for you today is really to equip you with the knowledge to truly understand these organisms, what makes them unique, their incredible diversity, and why they're so vital.

You know, from the forest floor to our dinner plates and even as plant pathogens.

Right.

We'll help you recognize and appreciate them without needing a single diagram, just by focusing on their core characteristics and the amazing forms they take.

Think of this as your shortcut to getting basidiomycota.

We'll break down their defining features, explore their three major subflood, and highlight some, frankly, mind -blowing examples that show just how adaptable life can be.

So let's start with some common ground.

Basidiomycetes are part of the subkingdom Decaria, just like ascomycetes, which we've explored before.

I have.

They share fundamental features like microscopic threads called hyphae, cell walls made of peaten, and the ability to produce complex, often visible, fruiting bodies.

But there are crucial differences, aren't there?

Things that really set basidiomycetes apart.

Oh, absolutely.

And understanding these differences is, well, it's key to appreciating their evolutionary success and their diverse forms.

Let's try and paint a picture of these distinctions, starting maybe with their internal structure.

Okay.

So while ascomycetes have simple pores in their internal cross walls, the septa, many basidiomycetes have this unique kind of barrel -shaped structure.

Think of it as a specialized guarded gate.

A gate.

Yeah.

It's called a dolapor, and it's often covered by membrane caps called parentheses.

This elaborate structure is really crucial because it carefully controls the movement of genetic material like nuclei between cells.

Okay, I see.

And that ties directly into their extended growth phase.

Now, rust fungi, they're a group within basidiomycota.

They actually have a simpler pore, often blocked by something that looks, well, like a tiny pulley wheel occlusion.

That careful control over genetic material sounds really important, because in ascomycetes, that stage where cells contain two compatible nuclei of the dicariophase, right?

That's quite restricted, isn't it?

Often only seen in the fruiting body itself.

But for basidiomycetes, it's a completely different strategy.

It absolutely is.

Basidiomycetes have what we call an extended dicariophase.

So when two compatible hyphae merge, the resulting bicarion where each cell carries two genetically distinct nuclei, that structure can grow for months, sometimes even years before sexual reproduction happens.

Ah, years.

Years.

This long -lasting partnership lets them colonize huge areas, I mean, impacting ecosystems on a really grand scale.

So the question becomes, how do we spot this dicariotic condition, especially when you can't always, you know, see the nuclei directly?

Well, one of the most brilliant visual clues, even under a microscope, is something called clamp connections.

Picture them as these little

nuclear bypasses or hooks found at almost every cross wall in the actively growing dicariotic hyphae of many basidiomycetes.

They're like a meticulous system.

They ensure that as a hypha grows and its nuclei divide, each new cell gets one nucleus of each compatible type.

Their presence is a really strong indicator of that dicariotic state.

Okay, so beyond their internal machinery, perhaps the most fundamental difference lies in how they produce and launch their spores.

Ascomyces, as you mentioned, keep their scores inside those sac -like structures, the assi.

Right.

Basidiomycetes do something totally unique.

The defining structure is the basidium.

It's typically a club -shaped cell where a nuclear fusion and meiosis happen.

But here's the kicker.

The spores, called basidiospores, they actually blow out, like tiny balloons, externally.

Externally.

Externally, from the ends of usually four tiny tapered outgrowth called sterigmata.

That external spore production is already pretty unique.

But the way these spores are launched, that's the really ingenious part, isn't it?

How does that microscopic catapult actually work?

It's a remarkable feat of microengineering, yeah.

It's known as ballista spore discharge.

Just before launch, a tiny droplet of fluid appears at one side of the spore's base.

It's called Buller's drop.

This droplet grows rapidly as water condenses onto it from the surrounding air.

Then, suddenly, this droplet merges with a film of water covering the spore surface itself, which dramatically shifts the spore center of gravity.

This sudden jolt, coupled with the pressure from the sterigma, essentially acts like a microscopic catapult launching the spore away.

Wow.

And this complex shared mechanism across so many diverse basidiomycetes, mushrooms, rusts, bracket fungi, it's powerful evidence they all evolved from a common ancestor.

It supports their monophyllae.

It's just a brilliant piece of biological design.

And I read that some mushrooms even cool their fruit bodies through evaporation, specifically to enhance that condensation for the spore launching droplet.

It shows how every little detail matters.

You're absolutely right.

Though it's worth noting that some basidiomycetes have actually lost this active spore shooting ability over evolutionary time.

Oh, really?

Yeah.

These are called sequestrate fungi.

Think of things like puffballs or earth stars.

The spores just stay inside the fruiting body, the basidioma, and they get released later by wind, rain, or even animals bumping into them or eating them.

So they rely on external forces.

Exactly.

And this loss of active discharge has evolved multiple times independently in different groups.

It's a classic example of what we call convergent evolution.

So for us, the casual observer, what does all this microscopic stuff mean?

The good news is you don't need an electron microscope to appreciate many basidiomycetes, right?

Their distinctive forms often give them away.

Precisely.

You already know what a mushroom looks like, or a puffball, or an earth star.

Their unique shapes are often telltale signs.

You might even spot their mycelia, the actual fungal threads, forming these delicate, sometimes fan -like patterns on decaying wood.

Right.

The basidiomycota are incredibly diverse, and they're organized into three major subfula.

Let's maybe begin our tour with the one most of us are probably most familiar with.

Sounds good.

That would be the subfulum agaricomycatina.

This is the huge group.

It encompasses virtually all the things you think of.

Mushrooms, bracket fungi, puffballs, earth stars, bird's nest fungi, stinkhorns, crust fungi,

and the jelly fungi, too.

So pretty much everything we picture.

Pretty much.

Their common names are often great clues to their visible features.

And this subfulum includes the massive class agaricomycetes with, what, over 21 ,000 species?

That's incredible.

But you mentioned taxonomy.

Modern science, especially using molecular data like DNA, is really shaking things up here, hasn't it?

It really has.

What we once confidently called a bulit, you know, that classic chunky mushroom with pores or tubes instead of gills.

Well, molecular data shows that related fungi can now look like almost anything.

Like what?

Like fungi with gills or thin crusts on wood or even stocked puffballs or earth balls.

It means that while identifying a specific species might still be possible visually, placing them into higher groups like families or orders can be quite a challenge now just based on looks alone.

Okay, so maybe let's explore some key examples to get a feel for this diversity.

Starting with the agariculs, the true guild mushrooms and their relatives.

Right.

So when you think of the mushrooms at the supermarket, you're likely picturing an agaricus.

It typically has that ring on its stem.

The gills are free, meaning they don't attach to the stock.

But within that same family, the agaricaceae, you find surprising diversity.

Like what else?

Well, consider the shaggy main coprinus caumanus.

It's famous for its gills that basically self digest into this inky black liquid as the spores mature.

It's called autolysis.

Ah, I've seen pictures of that.

Yeah.

And its desert relative, pedaxis, has completely lost that active spore discharge.

It's become a wind dispersed sequestrate form.

And of course you have the classic puffballs like like a perdon or calvasia, which are essentially just a ball of spores released by some external force.

No cap, no gills, no stock sometimes.

It's amazing how much variety exists in just form and dispersal, even among relatively close relatives.

Definitely.

Moving to another family, the strophariaceae, we find like psilocybe and stropharia.

These often contain the hallucinogen psilocybin.

So they're sometimes called magic mushrooms.

Right.

Those that bruise blue.

Exactly.

That blue bruising is a key characteristic due to the psilocybin oxidizing.

Then there's the enormous genus quaternarius in the quaternariusae.

I mean, over 2100 species.

They're known for their rusty brown spores and this delicate web -like partial veil called a cortina that covers the young gills.

Now some quaternarius species contain deadly toxins like orlanine, which damages the kidneys.

Important to know.

Very.

But interestingly,

one species, quaternarius caprata, used to be called rosites, is actually a well -known edible.

And I think you mentioned some of these are becoming sequestrate too, like losing their gills.

That's right.

Faxotero gaster, for example, looks like a quaternarius that just never opened up.

The cap doesn't expand.

The gills are convoluted, making spore dispersal difficult.

It really looks like it's honest way to becoming a truffle -like fungus.

It shows evolution in action.

That's fascinating.

And speaking of impressive fungi, have you heard about the humongous fungus?

Ah, Armillaria osteae.

Yes.

That single colony covering 600 hectares, estimated to be over a thousand years old.

It's part of the physolecreaceae.

It is.

And that family, or related ones, also give us some great culinary delights, like the shiitake mushroom, lontinula edodes, and the oyster mushroom, pleurotus, which remarkably is also predatory.

It actually traps and consumes tiny worms called nematodes.

No way.

A predatory mushroom.

Yep.

Gets its nitrogen that way sometimes.

And we can't talk about agaracles without mentioning Neomantaceae.

Ah yes, the famous and infamous Amanita.

Exactly.

This family includes the genus Amanita, known for some extremely toxic species like the destroying angel, Amanita virosa, or the death cap, Amanita phalloids, for anyone ever thinking about foraging mushrooms.

Listen up.

Yes.

Two critical identification features especially for Amanita are the vulvacheck for a cup -like remnant of a universal veil buried at the very base of the stem and the annulus, which is the ring left from the partial veil on the upper stem.

You must check for these.

Absolutely crucial.

And what about those tiny, cute cup things?

Ah, the bird's nest fungi like sciathus or nidularia.

Yeah, if you've ever spotted these little cup -shaped structures on rotting wood filled with tiny eggs, those eggs are actually little packets of spores called pyridials, and they get dispersed when raindrops splash into the nest.

It's quite neat.

Nature is clever.

Okay,

so beyond the gilled mushrooms, you mentioned the bulltails.

They used to be thought of as just the chunky ones with tubes.

Right, the boletes.

But as was said, molecular data shows this order is incredibly diverse now.

Yes, it includes the classic boletes, but also some gilled mushrooms, crust fungi, stocked puff balls.

A fun recent example is Spongiforma squarepantsii.

Named after SpongeBob.

Apparently so.

It's a sequestrate bolete that looks kind of like a sponge, and economically,

many bulltails are hugely important as ectomycorrhizal partners with trees, especially conifers.

Genura like Suez and Rhizopogon form these vital symbiotic relationships, helping trees absorb nutrients.

Okay, now for something truly bizarre.

The stankhorns.

They're in their own order, full ilies.

No matter their shape, they all share one

very noticeable trait for spore dispersal.

Their strategy is, well, brilliantly disgusting.

They produce their spools mixed into this slimy, often foul -smelling goo called a gliba.

Think of the common stinkhorn, phallus or dictyophora, which has this delicate lacy skirt below the cap.

So the smell attracts?

Insects.

Exactly.

Flies, beetles, other insects are drawn to the powerful stench, which often mimics rotting flesh or dung.

They land, crawl around in the slime, pick up the spores, and then fly off, carrying the spores to new locations.

Clever, if smelly.

And some, like take it even further, they have these bright orange -red arms that look a bit like tentacles or rotting meat, providing both smell and visual cues to attract an even wider range of vectors.

Wow.

Okay, moving on from smells.

Many of the bracket fungi, those shelf -like things you see growing on trees, belong to the polyparalis, right?

That's right.

Many common bracket or shelf fungi are in this order.

And speaking of impressive fungi, the largest single -fungal fruiting body ever recorded was from a relative in this group, Fomadiporia ellipsoidea.

Found in China, it was over 10 meters long.

10 meters and weighed hundreds of kilograms.

Yep, 400, 500 kilograms.

Absolutely massive.

What's the secret to their sturdy, often woody structure?

How do they get so tough?

Well, their toughness often comes down to their microscopic structure, their hyphal systems.

We classify them based on the types of hyphae present.

Monomytic fungi have just one type, the generative hyphae, which are thin -walled and septate, so they This could be thick -walled, unbranched skeletal hyphae for toughness or highly branched, thin -walled binding hyphae to hold everything together.

Right.

And then trimitic fungi have all three, generative, skeletal, and binding hyphae.

The classic example is the turkey tail fungus, Trimetes versicolor.

That's why it's so tough and leathery.

That makes sense.

We also classify these fungi by how they decay wood.

Brown rot fungi primarily digest cellulose and semi -cellulose, leaving behind the brownish -brittle lignin.

White rot fungi can digest lignin as well as cellulose, leaving the wood whitish and stringy.

And these cause a lot of damage to timber.

Right.

They do.

Significant decay in standing trees and structural timber costing millions annually.

But on the brighter side, some polypores like Laetiporus sulferius, the chicken of the woods, are actually choice edibles when they're young and tender.

Always good to find an edible one.

Now in the rustleys, we find two very common genera, rustla and lactarius.

What makes them distinct?

Well, rustla species are often known for their brittle flesh.

The cap and stem snap easily, kind of like chalk.

Lactarius, on the other hand, are the milky caps.

When you break their gills or flesh, they exude this milky or colored liquid called latex.

And microscopically, both genera have a unique feature.

Clusters of large, round, inflated cells called spherocysts mixed in with the normal hyphae.

It's the spherocysts that make the tissue brittle.

So the brittleness is a key identifier.

It is.

And what's really fascinating, again, showing evolutionary trends, is that some species from both rustla and lactarius have evolved sequestrate truffle -like forms.

They look totally different on the outside, but microscopically.

You still have the spherocysts.

Exactly.

They retain features like spherocysts and the characteristic amyloid ornamentation on their spores, these complex ridges and warts that stain dark blue -black with Meltzer's iodine regent.

It provides the surprising microscopic trail back to their gilled ancestors.

Evolution leaves clues.

And finally, within this big subphylum of Gherka micatina, we have the jelly fungi.

What's their story?

Right.

These are the ones you often see as gelatinous blobs or irregular shapes on of main groups.

The Dachromyces are often bright yellow or orange, kind of greasy -looking.

Their key microscopic feature is a unique Y -shaped basidium, often called a tuning fork basidium.

It has two long prongs, or sterigmata, that shoot the spores.

A tuning fork, okay.

Then there are the tremellomycetes.

These are also typically gelatinous, sometimes more brain -like or lobed.

And surprisingly, many of them aren't just decay fungi.

They're actually parasites.

Parasites.

On what?

Often on other fungi that are decaying the wood, so they're kind of hyperparasites in a way.

What's their broader impact, then, beyond just looking like jelly?

Well, it gets interesting because some tremellomycetes also have an anamorphic yeast stage, a single -celled phase.

And the genus Cryptococcus, which belongs here, actually contains some significant human pathogens, causing diseases like Cryptococcosis, especially in immunocompromised individuals.

Wow.

Okay, so from mushrooms to jellies that can be pathogens, that's quite a range.

Now let's shift gears to our second subphylum.

This one might not give us many edible delights, but it causes massive agricultural problems.

The Pucciniomycatena, home to the notorious rust fungi.

That's right.

These are hugely significant fungi economically, causing destructive rust diseases on all sorts of plants, including major crops.

Microscopically, they generally feature those simpler septal pores, often with the pulley -wheel occlusions we mentioned earlier, not the complex allopores of most Agaricomycatena.

And their parasites.

Yes, all rust fungi are obligate parasites of vascular plants.

That means they must live on a living host plant to survive and reproduce.

They can't just live on dead material.

And they often have very narrow host ranges, sometimes infecting only specific species or even specific varieties of a plant.

What's truly astonishing about rust, though, is their incredibly complex life cycles.

It's not straightforward, is it?

Not at all.

They don't typically produce mushroom -like fruit bodies.

Instead, they can produce up to five different kinds of spores throughout their life cycle.

Five.

Five.

And often, to complete that cycle, they need to alternate between two completely different, unrelated host plants.

We call this heteroecism.

That sounds incredibly complicated.

Can you walk us through an example?

Sure.

Let's take the classic example.

Black stem rust of wheat, caused by Pucciniograminy subspecies treatise.

This is what we call a macrocyclic, all five spore stages, and heteroecious rust.

It requires two hosts,

wheat and the common barberry bush.

Okay, wheat and barberry.

Right.

So, briefly, it starts in spring.

Basidiospores, which are produced from overwintering teliospores, infect barberry leaves.

On the barberry, the fungus goes through sexual reproduction, involving structures called spermagonia and asia, producing dichariotic asiospores.

Okay, stage one on barberry.

These ischiospores are then released and can only infect wheat.

On the wheat, the fungus forms reddish -brown pustules called urodynia.

These release millions and millions of urodyniospores.

These are the summer spores, or repeating spores.

Ah, the ones that cause the epidemic.

Exactly.

They're dichariotic, wind -dispersed, and they infect more wheat plants, leading to massive epidemics that can devastate crops.

Later in the season, as the wheat matures, these same pustules, the urodynia, switch to producing dark, thick -walled, two -celled teliospores.

These are the winter spores.

Stage three.

Right.

Karyogamy, the fusion of the two nuclei, happens in the teliospore, making it deployed.

It overwinters in this state.

Then, in the next spring, the teliospore germinates, undergoes meiosis, and produces a short, four -celled basidium, which releases new haploid basidiospores.

Stage four.

And these basidiospores… Have to land back on a barberry bush to start the whole thing over again.

Precisely.

It's an incredibly intricate cycle.

So, the core takeaway here is that understanding this intricate two -host cycle is absolutely crucial for controlling these devastating diseases.

Removing the alternate host, like barberry, can break the cycle.

Exactly.

That was a major control strategy for a long time.

But it's complicated because different races of pochiniograminis are constantly evolving through mutation and genetic recombination on the barberry host, overcoming resistance bred into wheat varieties.

It's a constant battle for plant breeders.

It sounds like an arms race.

Are there other significant rusts?

Oh, many.

There's gymnosporangium, which causes cedar apple rust, dramatically alternating between junipers, cedars, and apple or pear trees.

On the juniper, it forms these spectacular orange gelatinous telial horns in wet spring weather.

There's also crinartium ribicula, causing white pine blister rust.

Another heteroecious rust, alternating between five -needle pines and ribed species like currants and gooseberries, and hemolea vastatrix, the coffee rust, which famously devastated coffee plantations in Sri Lanka in the late 1800s, causing the country to largely switch to growing tea instead.

History changed by a fungus.

Indeed.

And one truly wild adaptation.

Euromyces psii infects a type of spurge, euphorbia cyperitius.

It actually manipulates the host plant, causing it to form pseudoflowers.

These are rosettes of yellow leaves that look remarkably like real flowers, even producing nectar.

Why would it do that?

To attract insects.

The insects visit these fake flowers, attracted by the color and nectar, and inadvertently transfer the fungal spermatia, allowing the fungus to undergo cross -fertilization.

It's mimicking pollination for its own sexual reproduction.

That is absolutely wild.

Okay, finally, our third subphylum,

the oestilogenomycotina.

This group contains the smut fungi.

Right.

Like the rusts, smuts are also parasites of vascular plants, primarily andeosperms or flowering plants, but they have their own unique way of operating.

How do they differ from rusts?

Well, there are several key differences.

While they also produce basidiospores, often from overwintering teleospores, smuts never require two hosts to complete their life cycle.

They are autoetious.

Okay, only one host needed.

Correct.

Also, many smuts can actually be grown in culture, often as a yeast -like state.

This means they are facultatively biotrophic, whereas rusts are obligate biotrophs.

They must have the living host.

Oh, okay.

Smut infections are also usually systemic, spreading throughout the host plant's tissues, unlike the often localized infections of rusts.

And perhaps most visibly, the smut tiliospores typically replace host organs entirely in ovaries, anthers, kernels, forming masses of black powdery spores, rather than just forming pustules on the surface like rusts.

That organ -specific attack is quite fascinating.

You mentioned replacing ovaries or anthers, for example.

Sure, Oosilago violacea causes anther smut in plants of the Karyophyllaceae family, like Celene.

It infects the plant systemically, but the spores only appear in the anthers, replacing the pollen with a mass of dark purple tiliospores.

Pollinating insects then spread the spores.

So it hijacks the plant's reproductive system.

Exactly.

And in corn smut, caused by Oosilago matis, the fungus causes kernels on the cob to swell up into these large distorted gray masses,

which eventually rupture to release clouds of black tiliospores.

Why do they target these specific plant organs,

like kernels or anthers?

It's clever resource allocation.

The fungus targets organs where the plant is actively directing high energy resources, sugars, nutrients for its own reproduction or storage.

The fungus essentially diverts these resources for its own spore production.

Which is bad for the plant and often bad for us if it's a crop.

Usually, yes, but in a delicious twist of fate, at least two smuts are actually widely eaten.

Eaten smut.

Yes.

Corn smut, those galls caused by Oosilago matis, are known as hootlacoche in Mexico.

They're considered a delicacy, harvested before the spores mature, with an earthy, mushroomy flavor.

I had no idea.

And another one, Oosilago esculenta, infects wild rice species in Asia.

It causes the stems to swell up, hypertrophy, and these swollen stems are eaten as a vegetable in China.

Amazing.

But other smuts are serious problems.

Definitely.

For example, bunt, or stinking smut of wheat, caused by species of teletia, like teletia caries.

It replaces the wheat kernels with a greasy, black mass of teliospores that smells distinctly like rotting fish, hence stinking smut.

It reduces yield and contaminates the grain,

and breeding resistant wheat strains has proven very challenging.

So another ongoing battle.

And just briefly, there's another class in this subfulm, the exobasidiomycetes.

A key example is exobasidium.

It doesn't form a big fruit body, but instead forms a whitish layer of basidia, directly on the surface of host plant leaves or flowers, often causing galls or reddish discoloration.

Okay.

So what does this all mean?

We've really journeyed through an incredible diversity within the basidiomycota today, from the familiar supermarket mushroom to that hidden humongous fungus, from the deadly amanita to the economically devastating rusts and smuts, and even those bizarre stinkhorns relying on insects.

You've now got, hopefully, a verbal toolbox to help you understand this kingdom's key features.

Things like dollopores, clamp connections, the amazing ballista spores, and their unique, often really complex, life cycles.

Absolutely.

And if we connect this to the bigger picture, the basidiomycota aren't just some random collection of fungi.

They are absolutely vital players in our world.

They're critical decomposers, breaking down tough plant materials like lignin.

They're essential symbionts, like the mycorrhiza, helping trees grow.

And yes, they're also potent plant pathogens, constantly evolving and interacting with our world, often in unexpected ways.

Which really leaves us with an important question, maybe something for you to ponder.

Considering these complex adaptations and these often very intricate life cycles, especially things like the host alternation and rusts, how might global changes,

things like climate shifts, or changing agricultural practices, or moving plants around the world, how might these human actions impact the delicate balance of these fungal relationships and their crucial roles in our ecosystems?

That's a really important thought.

The more we learn about these hidden kingdoms, the fungi, the more we appreciate just how intricate the web of life around us truly is.

Thank you so much for joining us on this deep dive into the basidiomycota.

My pleasure.

And a big thank you to the last minute lecture team for making this exploration possible.