JOHN YANG: Scientists to say that 80% of the Earth's species are not yet known, and even as more are identified, more are disappearing.

Sometimes we don't know what's being lost until it's too late.

On this Earth Day, we begin our series looking at what it takes to save plants and animals.

We call it "Saving Species."

And our first installment looks at the world of plants.

KENNY SILVEIRA, Plant Specialist, U.S. Botanic Garden: I am pulling off the fruits of this cactus.

JOHN YANG: Seed by tiny seed, meticulous and for some mundane work.

KENNY SILVEIRA: The little black dots that are coming out are the seeds of this cactus.

JOHN YANG: This is how you save a species.

Kenny Silveira is one of the dozens of horticulturalists at the U.S. Botanic Garden in Washington D.C., who are working to give some of the world's most endangered and rare plant species a better chance of survival.

The Botanic Garden which is part of Congress is a living plant museum with 44,000 fascinating plants with intriguing stories spread across a conservatory and a production facility.

These are from all over the world?

SUSAN PELL, Executive Director, U.S. Botanic Garden: They are so â| JOHN YANG: Executive Director Susan Pell let us through the mist, heat, and humidity stopping to talk under a giant leaf of the endangered corpse flower.

SUSAN PELL: I can tell you that about 34% of all of the plants in the United States are at risk of becoming endangered.

We see similar numbers globally with that where there's about 40% of global flora is at risk of extinction.

JOHN YANG: Scientists say the planet is currently at the beginning of its sixth mass extinction, when a high percentage of biodiversity, animals, plants, trees die off.

What's driving this, is it climate change?

SUSAN PELL: Certainly climate change is a huge factor and the risks that we see to our world's flora.

But there's other factors as well.

Certainly the developments from, you know, wild lands into agricultural use or buildings.

Another factor in there is the introduction of invasive species.

So the transportation of species around the globe and introducing them into areas in which they didn't evolve, really, most of the driver of extinction is human activity.

JOHN YANG: Experts estimate the world was losing species of all kinds and a rate between 1000 and 10,000 times higher than the natural extinction rate.

For conservationists, it's a race against time to do whatever they can to save species and their ecosystems.

SUSAN PELL: Plants are, you know, the keystone species and pretty much every habitat and by saving the plants saving the habitats that they're on we're also saving all the other biodiversity.

And, of course, biodiversity has a lot of benefits to, you know, our global climate, certainly to us as individual people.

JOHN YANG: In Australia, lawmakers set aside 30% of the entire continent to protect endangered plants and animal species and their habitats.

In South Africa, scientists are working to get rid of an invasive species that's clogging waterways, the water hyacinth.

In Albania, protesters are trying to stop development projects and an important migratory bird sanctuary and add a United Nations Conference in December 188 nations reached a landmark agreement to halt and reverse the destruction of nature by the end of the decade.

SUSAN PELL: We're entering our Hawaii room and the conservatory.

JOHN YANG: An ambitious goal institutions like the U.S. Botanic Garden are trying to help achieve.

SUSAN PELL: A cabbage on a stick or Brighamia insignis.

And this plant is extinct in the wild in Hawaii.

Originally, the seeds were collected from these plants from a cliff face and Hawaii so botanists had to actually repel down and collect the seeds from the plant.

And there are many stories about imperiled plants where they were down to one population or a few individuals and botanist or horticulturist went out and collected seeds from the plants or cuttings from the plants to bring them into cultivation to save them.

JOHN YANG: Part of saving these plants is understanding them better.

Pell showed us one plant a member of the a -_-_ 00:01:40 white family, she had never seen bloom before.

SUSAN PELL: If you look down in here, you'll see a little polka dots.

If you look a little deeper, there's some bigger polka dots.

Each of those little dots is a single individual flower.

JOHN YANG: And you said you'd never seen these sort of â| SUSAN PELL: I have not seen this species in bloom.

You know, we've been propagating it for a couple of years.

And when we received it, not everything was identified.

But prior to this bloom, we didn't know what species it was.

JOHN YANG: Scientists estimate only 20% of the Earth's species have been identified, which keeps us on the lookout for unknown plants with untapped potential.

SUSAN PELL: This plant right here, Madagascar periwinkle is a very common garden planet.

People love this.

It's for its beautiful pink flowers and what sometimes white flowers and they stay in bloom for a long time.

But this is one of the most important medicinal plants that we -- that we have in our collection.

Compounds from this plant has really saved thousands and thousands of lives by making the survival rate of childhood leukemia go from 10% to 90%.

JOHN YANG: So is this plant under threat?

SUSAN PELL: It is under threat in its native habitat.

It's really being destroyed due to slash and burn agriculture.

But it's so, you know, a really interesting conservation story.

And a really a story about the importance of learning as much as we can about species.

JOHN YANG: Take a took a look at here.

So species also rely on each other.

Plant mezzo cotton mauritiana (ph) has a special animal partner.

SUSAN PELL: Has these beautiful purple flowers.

JOHN YANG: Oh, wow.

SUSAN PELL: What do you see there?

JOHN YANG: Little red dots.

SUSAN PELL: Yes, so those little red dots are the nectar.

So typically in a flower, you don't really see the nectar when you look into it.

Because it's clear, but this one is actually pollinated by a native gecko of Mauritius.

And the gecko can see the nectar in there, knows his going to get a reward, and we'll go in and retrieve that nectar for a snack, but also in the process will pollinate these flowers.

JOHN YANG: Pollinators are vital and if they disappear or dwindle, it leaves plants in peril.

SUSAN PELL: That little stalker it's called the petiole.

This is what this trunk like structure in.

JOHN YANG: The massive and endangered corpse plant is famous for its rare and stinky bloom, which is what attracts pollinators.

SUSAN PELL: Their male flowers mature after their female flowers do.

And so they don't self-pollinate because of that.

But what that also means is you can't save the pollen and pollinate your own blooms.

And so gardens around the world will share their pollen, just literally FedEx and mail it to another garden overnight for them to pollinate their plants and grow up seeds.

JOHN YANG: This is in a way sort of like breeding programs at zoos where they'll have males and females traded around for endangered species?

SUSAN PELL: That's exactly right.

The idea there is to create intentional breeding programs so that we can understand the diversity that's already in cultivation and use that knowledge to inform how we would share pollen with other gardens.

JOHN YANG: So we're going from climate zone to climate zone here.

SUSAN PELL: Yes, absolutely.

JOHN YANG: From the tropics to the desert, Pell showed us a rare cactus from the Florida Keys that illustrates the collaboration among horticulturalists at institutions around the country.

SUSAN PELL: When we have a very rare plant in our collection, what we like to do is make sure that it is represented in other collections elsewhere.

So if something happened to our collection, it would still survive.

JOHN YANG: The purpose here is to make sure that these survive even if not in the wild in a collection?

SUSAN PELL: That's exactly right.

So the primary goal is always to have them survive in the wild.

But if that's not possible, then we want to at least make sure that species survives in cultivation.

JOHN YANG: As Kenneth Silveira toils to keep another rare cactus and cultivation one seed at a time he says there's nothing else he'd rather be doing.

KENNY SILVEIRA: All the species and everything else is such a wide range of things to get to work with.

I mean, I'm never bored, because it's keeps me always busy.

So I really can't picture doing anything else.

JOHN YANG: And for Silveira, even the cactus splinters are worth it.