Chapter 22: Phylum Basidiomycota: Other Basidiomycetes

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.

What if some of the most impactful organisms on earth are kind of hidden in plain sight, often overlooked?

Beyond the familiar button mushroom on your pizza, there's this whole universe of fungi.

Yeah.

Surprising structures, really bizarre life cycles, and they have these profound effects on our world.

Absolutely.

You've probably walked past countless examples without even knowing it.

It's completely true.

They're often literally underfoot or maybe clinging to a dead branch,

but their influence, it spans from the food we eat to the actual health of our ecosystems and even, well, our own bodies.

Right.

These aren't little curiosities.

They're essential players.

Welcome to the deep dive.

Today, we're taking a bit of a shortcut to understanding this fascinating, often hidden world.

We're plunging into the phylum Mycidia mycota.

We're drawing on a pretty dense chapter from an introductory mycology text.

Our mission for you today is to unpack all those intricate details,

structure, reproduction, physiology, genetics, taxonomy, and their ecological and medical importance.

Make it accessible, right?

Exactly.

Make it accessible and hopefully really engaging.

We'll start with the big picture.

Give you a broad sense of this fungal group before we zoom into the specifics, the processes, individual organisms.

The goal is really to help you get those aha moments without feeling totally overwhelmed by the complexity.

Think of us as your guides.

Exactly.

No, not at all.

Historically, it was really challenging, particularly for a group we often call the jelly fungi.

Jelly fungi.

Okay.

Yeah.

Imagine trying to sort things when their key identifying features seem incredibly varied.

Their basidium morphology, that's the little structure that makes the spores.

Right.

It was so variable that mycologists, well, they struggled for a long time to group them consistently.

So given that kind of chaos, what was the breakthrough?

How did we finally start making sense of these

shape sisters?

Modern science, really.

It came down to combining incredibly detailed microscopic analysis.

Looking at what?

Things like their internal spindle pole bodies, crucial for cell division, and these really intricate septal pore complexes within their hyphae, their fungal threads.

Okay.

Tiny detail.

Tiny, but significant.

And then combining that with cutting edge RDNA sequence analysis,

genetic fingerprinting, basically.

Ah, the DNA evidence.

Exactly.

That molecular data was transformative.

It helped clarify relationships, settled a lot of the taxonomic debate, and gave us a much clearer evolutionary map.

So like microscopic detective work plus genetic ancestry tests for fungi.

That's a great way to put it.

A very powerful combination.

And you mentioned jelly fungi.

So what are the main groups we're going to explore today within basidiomycota?

Well, we'll definitely delve into five orders often lumped together as jelly fungi.

That's auriculariolus, ducromycetales, ceratobasidialis, tulacinalilis, and tremolilis.

But we'll also touch on some other significant groups.

They might not be gelatinous, but they share interesting features like the simple septate fungi, things sporidialis, septobasidialis, and

exobasidialis.

Some of these actually have surprising links to maybe more notorious fungi, like rusts or smuts.

Interesting.

Let's start with those jelly fungi then.

What makes them jelly -like?

Is it just the texture?

Pretty much.

Their defining characteristic is that often gelatinous sort of jelly -like consistency of their basidiocarps, their fruiting bodies when they're moist.

Okay.

Think of them like soft rubbery blobs or maybe ear -like shapes coming off wood.

But it's more than just texture.

It's a key adaptation.

An adaptation for what?

What does being squishy let them do?

Well, they're remarkably efficient and resilient.

Many are incredible spore producers.

Right.

And that jelly -like nature gives them a huge advantage.

They can tolerate repeated wetting and drying cycles.

So they don't just die out when it gets dry.

Exactly.

They can shrivel up, almost disappear in dry weather, then plump right back up with rain and start making spores again.

Multiple crops, you could say.

Wow.

There was this one species, Exidia glandulosa, observed sporulating 20 times over seven months.

20 times?

Yeah.

Producing something like 6 ,500 spores per hour per square centimeter within just a couple of hours after getting wet each time.

It's this ability to pause and restart sporulation, a really clever survival trick.

That is incredible efficiency from a little blob.

Okay.

Let's zoom in.

Cremoles.

What makes this order stand out?

Okay.

Cremoles.

They have this really distinctive dimorphic life cycle.

Think of it as having two forms.

Two forms.

Yeah.

Sometimes they exist as tiny single -celled yeasts just budding away like baker's yeast.

Other times, they form a more complex network of threads, a mycelium, where their cells are paired up dicariotic, we call it, meaning two nuclei per cell.

Dicariotic, right?

And these mycelial forms often use these clever little bridge -like structures called clamp connections on their hyphae.

Clamp connections, I remember those.

They help distribute the nuclei.

Precisely.

They ensure the genetic material is perfectly distributed as they grow.

It's crucial for their reproduction and success.

And their internal structures are specific too, you mentioned.

They are.

They have what are called

Delaporcepta.

Picture a microscopic donut shape in the wall between cells.

Okay.

But it's a swollen donut with these intricate membranous cups on either side of the central pore.

Wow.

Complex.

It acts like a sophisticated gatekeeper, controlling what moves between cells, nutrients, signals, that sort of thing.

Very important for coordinating the fungus.

Their basidia, the spore factories, are also distinct, usually divided into four cells by walls running lengthwise or diagonally, not across like many others.

Different from the standard model.

Yep.

And their reproduction.

Governed by a complex, modified, bifactorial mating system ensures genetic diversity.

So definitely not your average fungus.

Where do we actually find these in the world?

Well, many are mycoparasitic.

Meaning they feed on other fungi.

Exactly.

Parasites on other fungi, whether other basidiomycetes or even ascomycetes, some just stick onto the host hyphae with little branches called hostoria.

Okay.

But here's where it gets really wild.

Some, like a species called Tetragoniomyces eulogenosus, actually form a direct connection, like a pipe, between the parasite cell contents and the host cell contents.

Through the cell walls?

Yes.

Through tiny pores in their cell walls.

It's incredibly intimate parasitism.

They're basically sharing cellular fluids directly.

That is mind -blowing.

And I hear some are commercially important, not parasitic.

Absolutely.

Tramella fusiformis is a huge one, often called snow fungus or silver ear fungus.

Right, I've seen that.

It makes these large, white or transparent gelatinous structures, lots of thin blade -like lobes.

Can get pretty big, maybe 10 centimeters across.

And we eat this?

Yes.

Grown commercially for food and traditional medicine, especially in China.

It's been domesticated since around 1800 A .D.

And the scale is massive, think.

53 ,000 metric tons produced in just one year back in 1989, 1990.

53 ,000 tons.

Yeah.

And you might also just stumble across Tramella mesenterica witch's butter.

Bright yellow -lobed gelatinous, often on dead branches.

Witch's butter.

Okay.

Yeah.

That's a

philobosadiela neoformans.

Ah, yes.

This one's critical from a medical perspective.

Philobosadiela neoformans is the sexual state, the teleomorph of cryptococcus neoformans.

Cryptococcus, okay.

That rings a bell.

A human pathogen.

A major human pathogen, yes.

It's heterothallic, needs two mating types to reproduce sexually.

It produces these haploid yeast cells that reproduce by budding.

Like the yeast phase you mentioned.

Exactly.

And crucially, these yeast cells are often surrounded by thick, protective mucopolysaccharide capsules.

Protection from what?

From our immune system, primarily.

Helps them evade detection and destruction.

The most significant natural source for humans is, unfortunately, weathered pigeon droppings or soil enriched by bird droppings.

Pigeon droppings.

Seriously.

Seriously.

Human infections usually start when these yeast cells are inhaled into the lungs.

Okay.

But what's really concerning is its tendency, its propensity, to then spread through the bloodstream.

Where'd it go?

Often to the brain and the meninges, the membranes covering the brain and spinal cord.

This leads to cryptococcus.

A serious and often fatal infection, especially in people with compromised immune systems like AIDS patients.

That's incredibly serious.

And there's a geographic twist, too.

There is.

An interesting variety.

C.

neoformans var gaudii has a distinctly tropical distribution, historically.

But now it's specifically linked to certain eucalyptus species.

Eucalyptus.

Like the trees.

Exactly.

So it's this weird situation where an introduced plant, eucalyptus, has become associated with a human health concern because the fungus thrives around these trees.

It's a new kind of foreign pathogen issue.

Wow.

And we can track these strains using genetics.

Yes.

Molecular techniques like RDNA fingerprinting are crucial for identifying different strains, distinguishing gaudii from neoformans, and understanding their spread in ecology.

Okay.

Fascinating and a bit scary.

Let's move on to the auriculariales.

This order has also seen taxonomic shifts.

It really has.

Historically, this order was defined by having basidia divided by transverse walls straight across.

But modern RDNA analysis completely shook that up.

It showed that many species with tremoloid basidia, remember, those divided lengthwise or diagonally, are actually very closely related to the original auriculariales members.

So genetics rewrote the family tree again.

Precisely.

It highlights how our understanding is constantly refined by this molecular data.

The relationships weren't what we thought based purely on morphology.

So what features define them now with this updated view?

Well, they have unique biglobular spindle pole bodies, those internal structures for cell division.

Their septa, the cross walls, have a clear swelling around the central pore.

And critically, their septal pore caps are continuous or nonperforate.

Meaning no holes in the cap over the pore.

Exactly.

Unlike some other groups, the cap seals off that pore.

They also use that bifactorial mating system we mentioned earlier.

Ecologically, most are sap robes.

Decomposers.

Yes.

Primarily decomposing dead wood.

Hugely important for nutrient cycling in forests.

And these are also big players economically, like the tremella.

Definitely.

Species of auricularia are some of the largest and most common jelly fungi.

You know them as wood ear or ear fungus.

Ah, yes.

The ones in Chinese food sometimes.

Exactly.

Distinctive brown, rubbery, flap -like, or ear -like structures.

They can get quite large, four to six inches across.

And their cultivation history is ancient.

Auricularia, auricularia judei, for instance, was cultivated in China way back in 600 A .D.

600 A .D.

That's incredible.

It is.

And today,

auricularia production is mind -boggling.

400 ,000 metric tons globally in that same 1989 -1990 period.

400 ,000.

That dwarfs the tremella figure.

It really shows their massive cultural and economic importance, especially in Asian cuisine and traditional practices.

Amazing.

And their life cycle.

Yeah.

How do they go from a s'more to that big rubber ear?

Well, their main body is made of those binucleid hyphae with clamped connections.

Right, the dicariotic stage.

Yep.

Then in the fruiting body's fertile air, the hymenium, the cidia form, the two nuclei fuse karyogamy, then undergo meiosis, cell division, reducing the chromosome number.

This results in a four -celled basidium.

Okay.

Each cell produces a long outgrowth, a sterygma or epibasidium, which bears a curved basidiospore.

These spores can then germinate by growing a germ tube or forming little crescent -shaped spores called knidia, or by repetition basically making a new spore directly off the first one.

Lots of options.

Any other common ones in this group?

You might also see exidia glandulosa, again also called witches' butter, confusingly.

But this one's usually dark brown or blackish with little warts.

Also things like slogeotis, which is pink or orange and funnel -shaped,

pseudohydnum, which is stocked with tooth -like structures underneath, and tremelodendron, which looks more branched, almost coral -like.

Okay, quite a variety even within the ear funguses group.

Oh.

Next up.

Dachromyceae tails.

The tuning fork fungi.

Why that name?

It's a perfect description.

Their most unique feature is their basidium.

It's single -celled, but it's deeply divided, split almost in two, making it look just like a tuning fork.

Ah, I can picture that.

It's very distinctive.

Ecologically, these guys are important brown rotters.

Brown rot.

They eat the cellulose and leave the lignin.

Exactly.

They break down cellulose and hemicellulose in wood, leaving behind the darker, modified lignin.

You often find them on conifer wood think, park benches, picnic tables, fence posts.

Okay.

What do they look like?

Their fruiting bodies are typically small, maybe jelly -like or sometimes waxy, often yellow to orange.

The shape varies a lot.

Flat crusts, cushion shapes, little cups, even upright things that look like tiny teeth or spoons.

And how do they develop and spread?

Any clever tricks like the others?

Oh, absolutely.

Take Colossar acornia.

Sporulation can actually be triggered just by the wood surface drying out a bit.

Hyphae gather inside the wood, form a little starting mat, and then this small orange gelatinous spike shoots up rapidly into the mature fruiting body.

Triggered by drying.

Interesting.

And then there's Dachromyces deliquescens.

Its spores are long, curved, and typically become threeseptate -divided into four cells after they're discharged.

Each segment can then grow a germ tube or pop off little microkinedia.

But what's really neat is that their soft, gelatinous fruiting bodies also produce these binucleate cells that, when it gets wet, literally just slide down the jelly surface.

They slide down.

Yeah.

It suggests a really clever water -based dispersal strategy.

They use moisture itself to spread around.

Later, the mature tuning fork Bacidia form, meiosis happens, and two nuclei move into each Bacidia spore before it's forcibly shot off.

Using water currents.

That's very cool.

Okay, now let's tackle two orders together.

Ceratobacidiales and Tullus nolales.

What links them?

Both orders have hollow Bacidia, undivided Bacidia.

These form quite strigmata, or epibacidia, the spore stalks.

Crucially, their Bacidiospores can form secondary spores, which are also forcibly discharged.

It's a way to get another shot at dispersal.

Another round of spores.

Exactly.

The key microstopic difference is in those septal pore caps again.

Ceratobacidiales have caps with large perforations, big holes.

Tullus nolales caps lack perforations.

It's subtle, but important for telling them apart.

What was really fascinating here is their ecological roles, right?

They seem to play both sides beneficial symbionts and destructive pathogens.

That's the really compelling part.

It raises big questions about fungal specificity.

Why do some fungi help plants while close relatives attack them?

So both orders include species that form vital mycorrhizal relationships with terrestrial orchids.

Helping the orchids.

Absolutely essential, especially for orchid seed germination and seedling growth.

The fungus provides nutrients the tiny seed can't get on its own.

Okay, the helpful side.

What about the harmful side?

Well, then you have species like Thanatophorus cocoomerus, that's the sexual state of a fungus you might have heard of, Rhizotonia solani.

Rhizotonia.

Yeah, that sounds bad for plants.

It is.

It's a hugely widespread destructive soil -borne plant pathogen.

It attacks an enormous range of host plants all over the world, causes diseases like root rots, stem cankers, damping off of seedlings, even foliage diseases.

A real menace.

And it's hard to get rid of, I gather.

Extremely persistent.

Part of the reason is its structure.

It has this characteristic right angle, or nearly right angle, branching pattern of its hyphae.

It has dolporcepta, interestingly, and often a constriction near the branch point.

Okay.

But for farmers, the real problem is its ability to form sclerotia.

Sclerotia.

What are those?

They're these compact hardened masses of mycelium, kind of like fungal survival bunkers.

They can survive in the soil for years, resisting drying chemicals, everything.

Then, when conditions are right, they germinate and attack new plants.

Makes it a really stubborn agricultural problem worldwide.

Right.

Those survival structures make control really difficult.

Okay.

We've covered the jelly fungi with their complex septa.

Now let's switch to the simple septate fungi.

What's the big difference there?

The fundamental difference is right there in the name.

Their internal walls, the septa dividing their hyphae, are simple.

They lack those elaborate dolapor structures we saw in the tremolales and auriculariales.

Just a basic wall with a pore.

Pretty much.

It's a simpler internal architecture.

This affects how things move between cells, physiology, and how we classify them.

Okay.

First group here, spordiales, the basidiomycetus yeasts.

So, yeast, but in the basidiomycota group.

Exactly.

It broadens the whole concept of yeast beyond just the ascomycota ones we use for bread and beer.

This is a diverse group, includes genera like rhodosporidium, leukosporidium, that's osperon.

And what are their key features besides simple septa?

Well, they often produce teliospores.

These are thick -walled resting spores, kind of like the sclerotia we just mentioned, but typically involved in the sexual cycle.

Okay.

Can you give an example?

Sure.

Rhodosporidium spherocarpum.

It forms these red or orange yeast -like colonies.

Reproduces mostly by budding, like typical yeasts.

When compatible yeast cells fuse, they form a dicariotic mycelium again, that two -nuclei stage.

This eventually leads to the teliospores.

Inside those, karyogamy, nuclear fusion, and meiosis happen.

And then new spores.

Yep.

Eventually forming basidiospores, which then bud to start the haploid yeast phase all over again.

The whole cycle actually looks remarkably similar to that of smut fungi.

Smuts?

Interesting connection.

And what about mirror yeast?

That sounds cool.

Yeah.

Acesperon salmonecolor is one of the mirror yeasts.

They get that name because they produce ballistospores, spores that are forcibly shot off directly from little stocks, sterigmata, on their regular somatic cells, not just from basidia.

So they're launching spores right off their main body.

Kind of.

It's a pretty neat dispersal trick for a yeast.

Okay.

Next order.

Septobasidialis.

You said unique insect symbiosis.

This sounds really specialized.

It really is.

This whole order is basically defined by its obligate symbiotic relationships with scale insects.

Obligate meaning they have to live together.

Exactly.

The fungus can't live without the insect, and the insects in the colony depend on the fungus.

And their fooding bodies are totally different.

Dry,

crusty, not gelatinous at all.

Okay.

So what's the deal?

How do they interact?

It's fascinating.

Basidiospores land on an insect, germinate, and the fungus grows over it, forming this intricate, high -full mat like a protective crust covering the whole insect colony.

Fungal blanket for the bugs.

Sort of.

Underneath this perennial mat, the scale insects live, protected from predators, weather extremes.

Sounds like a good deal for the insects.

What does the fungus get?

Nutrients from the insects, likely.

But here's the trade -off, the really fascinating part.

The specific insects that the fungus penetrates and feeds on directly are not killed, but they are rendered sterile.

Sterile.

Wow.

Yeah.

It's this precise balance.

The fungus gets fed, the colony gets protection, but the directly parasitized individuals lose their ability to reproduce, ensures the fungus doesn't wipe out its food source, but maintains control.

A very controlled parasitism.

Nature is amazing.

What about their classification?

Where do they fit?

Well, their Basidia are divided transversely across.

They have simple septa, and they have a thick walled teliospore stage that acts as a probicidium, a precursor cell to the Basidium.

All these features show strong similarities to rust fungi.

Rusts like the plant diseases.

Exactly.

And sure enough, our DNA analysis confirms that septo -Basidialis are closely related to the rust fungi, despite these incredibly different lifestyles.

Wow.

Evolution takes strange paths.

Okay.

Last group.

Exo -Basidialis.

Goal -forming plant parasites.

Yep.

A small order, but economically pretty important.

They primarily parasitize flowering plants, especially in the Ericaceae family.

Ericaceae.

That's rhododendrons, blueberries.

Exactly.

Rhododendrons, azaleas, tea plants, cranberries, lowbush blueberries, that family.

Important crops in some cases.

So economic impact.

Definitely.

Exo -Basidium vexans, for example, causes tea leaf blister.

It's a serious problem for tea production in Asia.

And E.

vexini causes red leaf disease of lowbush blueberry, which can hit yields hard.

What do these diseases actually look like?

You said galls.

Yeah, they cause really dramatic changes.

Infected parts, leaves, flowers, stems swell up, get distorted,

form these gall -like growth.

They can look quite grotesque, enlarged many times their normal size.

Okay.

E.

vexini can turn blueberry leaves bright red, make them curl up and die.

E.

vaccine forms those distinct blisters on tea leaves, which can kill whole stems if it gets bad.

It's like the fungus forces the plant to make a home for it.

And microscopically, how are they doing this inside the plant?

They have these slender branched hyphae that grow between the plant cells intercellularly.

They have simple septa and no clamp connections.

Okay.

But the really key structures are their hostoria.

Hostoria again.

Specialized feeding structures.

Exactly.

But these are distinctive,

short, lobed structures that penetrate the host cell wall and membrane.

Think of them like tiny, multi -fingered probes sucking nutrients out.

They even have complex internal structures within the hostoria.

Wow.

Really specialized.

How do they reproduce?

Well, eventually, the fungal fertile layer, the hymenium bearing the basidia, bursts through the plant's outer layer, the epidermis.

This exposes the basidia right on the surface of the leaf or stem.

So spores are released right into the air.

Yep.

And their nuclear cycle in the basidium is again quite similar to rusts and smuts.

They produce usually four to eight basidiospores per basidium.

And the spores themselves are characteristic, often sort of banana -shaped and curved towards each other.

Banana -shaped spores.

Okay.

These spores can germinate directly with a germ tube or they can do that repetition thing, making secondary spores.

Both types can infect new plants.

How do they survive between seasons?

Some, like Evexini, can have perennial mycelium living inside the host's rhizomes, underground stems.

But most probably just survive as spores, maybe tucked away safely in the host plant's bud scales waiting for spring.

It's interesting too.

Isn't there a parallel with another group, the taffrina fungi, even though they're in a different phylum?

Absolutely.

It's a striking case of convergent evolution.

Taffrina are Ascomycetes, not basidium mycetes, but they also cause galls and leaf curls on flowering plants, grow between cells and form their fertile layer on the host's surface.

So similar problems lead to similar solutions, even across major fungal divides.

Precisely.

Nature finds effective strategies and sometimes finds them more than once.

What a journey.

We've gone from commercially farmed jelly fungi on our plates to these hidden pathogens causing devastating diseases in plants and people, and then these incredible symbionts managing insect colonies or helping orchids get started.

It really shows the sheer breadth of basidium mycota, their structures, their reproductive strategies, their ecological roles.

It underscores this huge, often unseen impact they have.

Unique structures,

complex life cycles, diverse physiologies.

They're truly master adapters, thriving everywhere from dead wood to living tissues, using this amazing toolkit of cellular tricks and reproductive strategies.

Their influence is just profound from the forest floor right down to the cellular level.

So what's the takeaway for you listening?

Maybe next time you see a patch of damp wood or a weird growth on a plant or even hear about a particular illness, consider the often invisible fungal network that might be at play.

The world under our feet, inside plants, even inside us.

It's teeming with these complex vital organisms.

Constantly shaping the world around us.

And there's always more to learn, isn't there?

Always more waiting if you want to take your own deep dive.

The more we understand these hidden kingdoms, the better we can appreciate their power and, well, their importance.

Couldn't agree more.

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

We really hope this exploration sparked your curiosity and hope you appreciate just how significant these remarkable fungi are.

Yeah, hope you found it interesting.

Until next time, keep exploring and stay well informed.