Brains and hearts.
Lungs and kidneys.
No, this is not an ingredient list for a zombie cookbook.
It’s just a few of the organs that animals like us have
to keep our bodies in working order.
But plants have totally different organs
— despite what you might have heard about artichoke hearts.
And unlike most of our organs,
which you can only see with an X-ray,
you’ve come across a lot of plant organs.
You’ve seen plant organs alive,
whether growing in the woods,
beside the road,
or in your bathtub full of houseplants.
And you’ve seen them dead —
severed plant organs piled on top of each other in bins.
There they sit beneath harsh white lights,
damp from routine mistings,
just waiting to be picked up and carried away.
Hi! I'm Alexis, and this is Crash Course Botany.
Grab your cart and coupons— we’re going to the grocery store.
[THEME MUSIC]
Like animals, plants are made up of organs,
or body parts that carry out specific functions
and consist of more than one type of tissue.
Not tissues like Kleenex;
tissues like groups of cells that look similar
and serve similar purposes in a living thing.
But plants have totally different modes of developing,
growing, and organizing their bodies.
That’s because they evolved from the simplest form of life,
a single-celled organism,
independently of animals like us.
In other words,
it wasn’t like there were single-celled organisms that evolved into plants,
that then evolved into animals.
The evolutionary ancestors of plants and animals diverged over a billion years ago,
and then each evolved on a totally separate path.
Which explains why our bodies work so differently from plant bodies.
Like, in both plants and animals,
there are these things called stem cells.
Stem cells are special because they are unspecialized.
They have the potential to become tons of different types of cells.
They’re like the clay you use in art class.
You could make it a vase, a mug, a bust of your favorite botanist.
Love you, Linda Black Elk!
For humans and other animals,
most of our stem cells exist only fleetingly
in embryos before they get used up to make our organs.
Which is perfect because we animals are born with essentially the same body plan
that we’ll carry into adulthood.
That means the number and location of our organs
won’t really change throughout our life,
barring surgery or injury.
In contrast, plants are always producing new organs
from the second they germinate, or begin to grow
— can’t stop won’t stop!
Clusters of stem cells, called apical meristems,
at the tip of every stem and root
continually produce the materials needed to build new body parts.
They also have lateral meristems that allow roots and stems to thicken as the plant grows.
The three main organs that comprise a plant body are stems, leaves, and roots,
and their presence is one of the defining characteristics of a category called vascular plants.
Non-vascular plants, by the way, are often low-lying plants like mosses
— and we’ll cover them in another episode.
But for now, we’re on the hunt for our rascally vasculies.
Stems provide the structural framework of the plant,
whether dainty daisy stems
or thick tree trunks
—yes, tree trunks are stems!
Stems are typically, though not always,
found above-ground and contain vascular tissue that supports the plant
and transports water and sugar throughout its body.
As we head down the grocery aisles,
we might not find a lot of stems,
mostly because the tissues that make them strong enough to hold up a plant
are a little too tough to be tasty.
Asparagus, though, is a great example of a stem:
we harvest asparagus plants when they’re still tender,
and we often snap off the bases that have become too woody to eat.
Stems also hold a plant’s leaves —
another crucial organ —
up to the sunlight.
That lets the leaves do their main job:
photosynthesizing, or converting carbon dioxide gas into sugars,
using energy from the sun.
To maximize their photosynthetic capabilities, leaves are often flat and wide
— which gives them more surface area —
and green, which makes them more efficient at harvesting light energy.
Their veins shuttle nutrients in and out of the leaf,
and the cells in between are packed full of chloroplasts,
the cellular machines responsible for photosynthesis.
Leaves are a lot easier to find at the grocery store—
their wide, frilly shapes give them away.
Lettuce, kale, spinach, cabbage — these are all classic leaves.
Some will still be attached to their original stems,
which show off their phyllotaxy
— or the pattern in which leaves grow around a stem.
So in asparagus, the little scales at the top of the spears
are leaves with beautiful spiral phyllotaxy.
The chunky part of kohlrabi is also a stem,
and its much larger leaves have spiral phyllotaxy as well.
At the point where each leaf meets the stem, there’s a bud,
which is a new meristem that has the potential to grow into a branch and
start producing its own stem and leaves.
Because of this, the leaf pattern determines the arrangement of the plant’s branches.
So the difference between a stem and a leaf is obvious, right?
I mean, you know which organ this is…right?
It’s trickier than you’d think!
Onions are bulbs, which means they’re mostly leaves
around a modified stem
that’s evolved to swell up and store food for the plant during the winter months.
So even an onion isn’t very straightforward.
Hey, they have layers!
A good rule of thumb is if the plant organ is bearing other organs, it’s probably a stem.
And the trick to telling stems apart from leaves is to look for a bud
nestled above the thing that looks like a branch.
If there’s a bud, it’s a leaf.
And now, for the third item on our list: roots.
Roots are the typically underground organs of a plant
that are responsible for absorption and anchorage to the soil
or…the face of a cliff!
[Alexis sings a rockin' guitar lick]
Plants are pretty hardcore!
Their epidermis, or outermost layer of tissue,
produces billions of tiny hairs that absorb water and nutrients,
and their vascular tissue transports the nutrients up to the stem and leaves.
The longer roots grow, the more they can explore the soil and absorb the good stuff.
If the root needs to branch off,
a new root with its own meristem
busts out from the center of the old one, Alien-style.
So yeah, roots come in a variety of shapes and sizes.
Many have also evolved functions beyond anchoring and absorption
such as storing food,
providing housing for helpful organisms like bacteria,
and exchanging nutrients with fungi underground,
like swapping chicken fingers for Lunchables beneath the cafeteria table.
And many roots, we eat!
In the produce section, you’ll find carrots, radishes, beets, and sweet potatoes.
All of these foods are storage roots that are filled with deliciousness
originally meant to help the plant through hard times,
like a dry period or cold winter.
The way to spot a root is that it should be an organ with no phyllotaxy
— meaning no pattern of leaves around it.
Now, you might be saying,
“Alexis, you’re forgetting about my favorite kind of root to eat—russet potatoes!
We’re talking the plant that birthed French fries and tater tots,
latkes and hash-browns.
The root that is so delightfully creamy
when mashed up,
it earned a place in the Hall of Fame of Side Dishes!
Why would you neglect such a versatile food
—one that’s even been honored with its own emoji?” [Angelic voices singing]
Well, pick up a russet potato
and you’ll find those little notches in the skin, called eyes.
And from those eyes, buds, branches, and leaves can grow.
On top of that, you’ll notice the eyes are arranged in a
suspiciously regular pattern…
Yep, russet potatoes have phyllotaxy.
Which means, unlike sweet potatoes, russets aren’t roots—
they’re underground stems!
I know, mic drop.
You might be wondering why, despite
all this hanging out in the grocery store, we haven’t mentioned two very common words yet:
vegetables and fruits.
The thing is, “vegetable” isn’t actually a botanical term.
It’s just a useful regular-person word to describe some edible plant parts.
The word “vegetable” could refer to stems, leaves, roots…
and even
—are you ready for this?—
fruits!
Okay, let’s rewind for a second.
So far we’ve only talked about vegetative plant organs,
which refers to a type of organ that contributes to a plant’s
overall growth and structure.
But plants also make reproductive organs
of a variety of different sizes, shapes, and colors,
which help them have plant sex and create plant babies.
Botanists have a vast and precise language for describing them,
including the word “fruit,”
which refers to a mature, ripened ovary containing seeds.
[Gameshow Host Alexis]: Welcome to Not a Fruit,
[Audience applauds] where the game is to name a plant
that’s not a fruit!
[Contestant Alexis]: Cucumber!
[Gameshow Host Alexis makes a buzzer noise]
[Contestant Alexis]: Eggplant?!
[Gameshow Host Alexis]: Also [buzzer noise]
[Contestant Alexis]: Zucchini??!!
[Gameshow Host Alexis makes a buzzer noise]
Nope, [Contestant Alexis sighs]
[Gameshow Host Alexis]: all fruits!
Meanwhile, some of the things we call fruits
aren’t fruits at all!
Like, the tasty part of the strawberry is actually the base of the flower,
not the ovary.
Strawberry fruits are technically the little nubbins that we would call seeds.
[mind blown noise]
And there is one food in particular that has been the subject of the
fruit/vegetable debate for centuries.
And that’s gotta be the tomato, like Theo here.
Let’s go to the Thought Bubble…
The year was 1886.
New York was a major port city,
and wholesalers were starting to introduce the U.S. to fruits
and vegetables from other countries by
shipping them across the ocean.
But there was some controversy over shipping regulations.
Whenever anyone imported vegetables,
they had to pay a 10% tariff on them,
while fruits didn’t have the same tax.
So when a guy named John Nix received a shipment of tomatoes
from the Caribbean and was forced to pay the vegetable tariff on it,
he was not happy.
He claimed that tomatoes weren’t vegetables—
they were fruits, so he should get his money back.
Theo was having…a bit of an identity crisis.
By 1893, Nix’s case had gone all the way to the United States Supreme Court.
During the trial, the witnesses
—which were not bananas and broccoli as you’d expect,
but humans in the produce industry—
debated multiple dictionary definitions of “fruit” and “vegetable.”
Nobody asked the tomatoes what they thought of all this.
Ultimately, the judge declared that despite any botanical similarities to fruits,
tomatoes were vegetables because they were, quote:
“…usually served at dinner in, with, or after the soup,
fish, or meat…, and not, like fruits generally, as dessert.”
And this remains true to this day in the U.S.
Even though tomatoes are botanically fruits,
they are legally vegetables.
What can I say?
People, like tomatoes, are messy.
Thanks, Thought Bubble! [Audience applauds]
[Gameshow Host Alexis] And we’re back with everyone’s favorite game show, Name a Berry.
Where the game is… you get it.
[Contestant Alexis]: Blackberries!
[Gameshow Host Alexis makes a buzzer sound]
[Contestant Alexis]: Raspberries!
[Gameshow Host Alexis]: Additional [buzzer sound]
[Contestant Alexis]: Mulberries?!
[Gameshow Host Alexis makes a buzzer sound]
[Contestant Alexis]: I don't wanna play this game anymore
According to the botanical definition, [crash]
a berry is a fleshy fruit that comes from a flower with a single ovary.
In a nutshell, [ripping sound] ow
blueberries and cranberries are pretty much the only fruits with
“berry” in their name that are actually berries.
Meanwhile, tomatoes, avocados, bananas
— yep, berries.
So now we have a pretty good feel for the rulebook of botanical body-building
—as in, forming bodies made of organs, not getting swole.
Plants evolved different rules than we did,
and through variation in just a few different organ types,
they’ve diversified into a magnificent kingdom
full of, as Charles Darwin put it, “endless forms most beautiful.”
Botanists have deciphered these rules and translated them into a precise and consistent language,
one we’ll be exploring in future episodes.
Sometimes that language is at odds with how we’re used to talking about plants in our everyday lives.
But now you know that when the doctor recommends 5 servings of fruits and veggies a day,
you have a variety of plant organs to choose from.
I say go wild and have plant organs for breakfast, lunch, and dinner.
[crunch]
Next time,
we’ll be zooming in on plant cells and hormones
—the tiny structures and chemical signals
that allow plants to do amazing things.
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Hey, before we go, let’s branch out!
What part of the plant is a Brussels sprout?
Find the answer in the comments!
[Gameshow Host Alexis]: Thanks for watching this episode of Crash Course Botany
which was filmed at the Damir Ferizović Studio and made in partnership with PBS Digital Studios and Nature.
If you want to help keep Crash Course free for everyone, forever,
you can join our community on Patreon.
I don’t know what that is…