Gardening Unplugged - Jurassic Garden

Gardening Unplugged - Jurassic Garden

w/Dr. Patrick McMillan

By Published June 19, 2023

In this edition of Gardening Unplugged, Dr. Patrick McMillan takes guests on a walk through time exploring the amazing ancient plant lineages and the origins of some our favorite flowering perennials in the garden. You can join Dr. McMillan, or one of our other expert horticulturalists, free at any of our four Open Nursery and Garden Days held throughout the year.


Video Transcription

So, we're going to do a tour of the Jurassic Garden here at Juniper Level Botanic Garden Plant Delights Nursery today and what we're going to be focused on looking at are plants that would have been around basically during the Mesozoic; during the time when dinosaurs were walking around. And I think that most people who have an idea of what those plants look like are going to be kind of surprised when we actually see the plants that actually were around at that time in some cases earlier. Because in your mind when you think about dinosaurs, now think back to when you were a kid and you get that dinosaur book, you're flipping through the dinosaur book. What do you see with the dinosaurs? Giant ferns, right, and cycads and palm trees. But and matter of fact most of the ferns that we have growing around us and growing in the gardens, most of those are no more ancient in lineage than the penstemon plant that's there. Most of the cycads, actually all the cycads that we have today, aren't ancient lineages of cycads. They still have the look of an ancient cycad that they're very distantly related to, the plants that were around when dinosaurs were here, but we're going to see that there are a lot of flowering plants in the garden who can trace their fossil history back to the Jurassic period. And in some cases, we think their molecular history, what we know about their DNA, pushes them back all the way to the mid- to late-Triassic period. Some of those are flowering and so we'll get it well most of those we can see flowering, so we'll get a good look at them, so we'll start over here, but I really want us to sort of take a march up to the top garden because there's so many more ancient plants up there. But one that we won't see another member of the genus in which I really want us to see is pawpaws. And this is a slender leaf pawpaw or slim leaf pawpaw which is a Asimina angustifolia. And pawpaws have a really unusual smell and as we walk around the garden, we're going to look at these really ancient plants and we'll find out that most ancient plants have something unusual about their odor. And that one does smell... how would you guys describe that smell?

You can crack it a little bit more if you need to get the smell. Spicy, tart.

Yes, okay yeah, a lot of people say it smells like a green pepper you know, doesn't it?

Pawpaw fruits, we think, were dispersed by elephants.

So, these oils that are in a lot of ancient lineages of plants are called ethereal. They’re ethereal oils but we call them primitive or ancient oils because their chemical composition is unique to what we call the basal angiosperms. And so, pawpaw is one of those. It's not the most ancient, but it is one that would have been around certainly by the early Cretaceous Period. So yeah, pawpaws, not something you might have thought dinosaurs running around through pawpaw patches but that's the case. So, we'll take a walk on up this way. The pawpaw is also interesting. You guys have seen a real pawpaw fruit, the big fruit on the larger pawpaw. Pawpaw fruits we think were dispersed by elephants.

So those great big fruits today have great big seeds. The seeds need to be scarified or they need to have been you know some of their seed coat really scraped through to germinate readily. And so, a guy named Dan Jansen came up with this idea that a lot of these fruits like avocados, pawpaws, that today other animals will eat them like foxes and raccoons will come and they'll nibble on pawpaws, and they'll eat around the seeds, but they don't really consume the seeds and take them away and do what the seed needs to do to germinate. Almost all the major lineages have been around for almost 100 million years.

So, we'll have a little dead time here because we don't have a whole lot of ancient plants around this part. And wait for everybody to catch up. I know I did a sprint across the garden there for a minute.

So, when we think about plants that have flowers, we call those angiosperms. And angiosperms basically have seeds that are covered with a fruit. We call them flowering plants but really what they are fruiting plants. And if you think about gymnosperms, gymno means naked seed rather than enveloped seed like angiosperm. A gymnosperm has a seed that's just sitting on top of a scale so if you think about a pine tree and a pinecone you have scales and then you have a seed that's naked. It's sitting, its gymno, it's right there on top of the scale and so we had to get, because we know gymnosperms are a more ancient group than flowering plants, we had to somehow get from a cone a scale with a fruit to an enveloped fruit that produce something that was attracting pollinators. And so, a lot of folks were thinking about what would the missing link look like? Well, when we look at this beautiful negeia that's here, this looks like a flowering plant. It's got great big wide leaves, right, that's what we think of a flowering plant having. This is a gymnosperm, this isn't an angiosperm, it's not a flowering plant. And one of the theories of where these things came from was, they came from plants that looked like flowering plants but we're actually still gymnosperms and we know now because we know the molecular heritage of most of these things that that's not the case. These things just happen to end up looking like flowering plants, but they didn't lead anywhere. They're evolutionary dead ends essentially. You can see up here what looks like flowers but they're not. That's like the the pine tree, they're little, tiny male cones full of pollen shedding anthers but they don't have a fruit. They're not a flowering plant, yet. So negeia and all the things that are related to it and things like ginkgo, ginkgo is a gymnosperm, looks like a flowering plant in its leaves. But it's not the group that led to flowering plants. What did lead to flowering plants is actually very, very interesting.

...modern cycads aren't any more ancient than most flowering plant lineages.

Cycads, the relative of cycads and flowering plants, share a common ancestor. So, from DNA studies now we think the most likely relative of closest relative to flowering plants look like this. And this a lot of folks call many of the cycas species the cycads that are in the genus Cycas, they sort of throw them together. They call them sago palms. They're not palms, they're not flowering plants, they're gymnosperms. Just like the pine tree here. But the cycads, and you probably know this if you're plant nerds this if you've got a cycad, cycads they say oh it's this ancient group of plants but no, the modern cycads aren't any more ancient than most flowering plant lineages. The modern cycads though however share an ancestor with flowering plants that looked like a cycad that is more ancient than either. So yes, that look would have been around when dinosaurs were roaming around North Carolina, but that actual lineage of plants probably wasn't around. However, they're really worth talking about the biology and we got one that had female cone on it last year over here so we can look at how they reproduce which is really interesting.

So, this cycad last year, instead of making leaves, it made a giant cone. And it's a female cone that this made because cycad plants are either males or females and the male cone on this would be a much narrower, much more like a pinecone, and the female cone is this massive structure that has seeds along the edges of the scales. So, if we actually take a scale out and look at it you can see it's just like the scale on a pinecone right, if we packed them close together, and the seeds are right here on the end of the edges of the pinecone looking structure. So, it's yes, it's so weird and so cycads are kind of like oh they're some of the characteristics are almost animalian yes because cycads have a very bizarre way that they get their pollen or their sperm in the case of cycads they get their sperm to the egg. the male and the female cones produce heat and they seem like great places for beetles to come and the male cones produce so much of this really rich nice fluffy pollen-like stuff that the beetles come in and get covered in it and they go to the female cone and transfer over the sperm cells and it has to go when it's wet because this these cells actually uh germinate if you will and let loose sperm cells that swim by cilia just like animal sperm cells swim to the egg and fertilize the egg. So, it's almost more like animal sex going on here than plant sex but indeed that's the way cycads actually reproduce. So, to get them to reproduce the way we make them this one didn't get pollinated successfully we tried but the male that we had shed all that that pollen earlier than the female was receptive, so it didn't work. So, she did all that last year and didn't produce any leaves and the end product was nothing unfortunately. but she'll live another couple hundred years and she'll do it again right.

Almost all the major lineages have been around for almost 100 million years.

So, palms, not a super ancient lineage. They've been around since the Cretaceous but almost all flowering plants have been around for almost 100 million years. Almost all the major lineages have been around for almost 100 million years. Charles Darwin called it an abominable mystery how flowering plants arose because if you look in the fossil record there's no flowering plants, no flowering plants, no flowering plants, then all flowering plants that seem to appear at the same time, so it was very confusing to him. Well one of the problems is flowering plants, plants in general, to preserve those fossils you need good mucky soil, and you need a time when you have a lot of water around to do that. So, at the time when we actually think flowering plants first appeared, in the late Triassic, it was a lot more dry area on Earth than there was wet and Triassic fossils are rather uncommon anywhere in the world. You find them in South Africa if you're in South America if you're in Colorado but there's not a lot of deposits of Triassic and the deposits aren't good at preserving really fine detail in most cases, so we don't have really good evidence much farther back than the mid Jurassic for any kind of flowering plant, all right. So, what does an ancient, ancient plant look like? We got one of the most bizarre right over here. [Laughter]

I'm going to grab a flower off the rhododendron, I'll meet you guys right here. I just want a single flower to compare between the ancient, a primitive lineage and a more modern lineage.

So, the plant right here is... one of you guys probably already know, your all plant nerds like me, right. This is anise shrub sometimes also they call it star anise. One of the species, Illicium varum is the source of the spice star anise. And the leaves have... guess what? A very unusual odor, similar to anise but not quite. It's one of those ethereal oils just like the pawpaw that we saw. So more advanced flowering plants like a rhododendron generally have a set number of parts. So, if we look on the back here, we can see five lobes on the calyx on the sepals. We have how many lobes of petals? Five, right. One, two, three, four, five, okay. You remember in school we learned monocot and dicot. Monocots three, dicots five, doesn't really work and there is no such thing as a dicot these days, but we still have monocots at least. It usually they have a set number of stamens and a set number of pistols. So that's an advanced flower. When we look at the illicium flower, and take a good look at that, it has strap-like things that kind of look like petals, but the very outer ones look like sepals. And the sepaly ones on the bottom of that thing kind of whirl, they spiral in, and they become longer, and they look like petals. And then those long petals spiral in they start to look like staminodes and the staminodes become stamens and the stamens spiral into the stigmas. And so what you actually can see in most of these most primitive flowers like water lilies and illicium are is actually a recapitulation of the evolution of each part because there were not set numbers in these early angiosperms and this angiosperm is really ancient. The things that are dicots, have two seed leaves like we learned in school, the ones that have two seed leaves and have weird flowers and ethereal oils and all these other things today we know they're not really dicots they're more primitive than either monocots or the rest of what we used to call dicots.

And we call these today basil angiosperms because if you think about the family tree they come out at the base and this one comes out at the base of the base of the basal angiosperms in a group we call the ANITA-grade. It's named after the orders and families that make it up (Amborella, Nymphaeales, Illiciales, Trimeniaceae, and Austrobaileya). Water lilies are part of a weird group called Austrobaileyales which includes Illicium, the ‘I’ in the ANITA and the Illiciaceae are in there and Trimeniaceae which is a weird group of Austrolasian things that you'll never ever see. So, these this is what the most ancient flowers look like and the most ancient lineage of plants on Earth the absolute base is still around on the planet rocking around out in New Caledonia in the middle of the Pacific Ocean it's a plant called ambarella. And the flowers look almost exactly like this. The other thing about ancient plants; they tend to have fruits. Because remember we had to go from a scale to a fruit. They have fruits that are really much more alike they're all mostly follicles. Our ambarella has an acidic carpal but most of them have follicles and a follicle is though if you had an ovule a seed here and you had it on a scale how could you protect it? Well, you could protect it by folding the scale together and fusing it along one margin. That's the most ancient type of fruit called a follicle. And guess what the star fruit think if you guys cooked with star fruit each one is a little follicle that pops open and has a seed in the middle it's the most ancient type of fruit it's a leaf that's been modified or a scale that's been modified into what we call a carpal. That's amazing to me that we can see that. And this one is so ancient that even though the leaves smell good I don't know if you can still smell the flower, it has a little faint odor there. Almost all basal angiosperms are not pollinated by bees. Now if you're rocking around on the planet 180-200 million years ago, there are no bees. Hymenoptera wasn't diversified yet. It would be the Cretaceous middle of Cretaceous Period before they diversified so it didn't do you any good to attract bees. There are no bees right but we're there were thrips which is what pollinates ambarella there are there were flies and there were beetles. And to attract those you smell like dead stuff right or poop. So, most of these ancient plants smell like manure or they smell like dead stuff like carrion. And this one is so ancient this lineage that it predates the evolution of mammals and reptiles probably weren't even that common. So, guess what it smells like? A dead fish. Isn't that amazing? Unbelievable. Not too strong.

Q: Were all the flowers really small?

A: No, there were big flowers too. Actually, let's look at a big ancient flower right here. We only have one species left blooming in the garden of this because most of them bloom early in the spring. But here is an ancient flower.

So, this is Magnolia yuyuanensis right. So, magnolias are basal angiosperms. Let's step out of the road so you guys aren't getting in the traffic. But what I want you to notice about this flower is that it has sepals that kind of spiral into you see how the outer sepal looks like a sepal this one looks it's got a little petally look to it. This one's like half petal half sepal right and as you move in the parts are obviously pedals, pedals, pedals, pedals, pedals, pedals, pedals, right. and then there in the inside of the Magnolia yuyuanensis is a very ancient looking structure. It has lots of stamens down here and it has the carpels with the pistols sticking out up here and look you can even see... you guys have all seen southern magnolia, it has a follicle just like we talked about over here. It's a folded over bract that pops open to release that red arrowed seed all right. So, magnolias. Guess what pollinates most of our magnolias?

Audience: Flies?

Flies pollinate some, Magnolia tripedalas is that one that attracts flies because it smells like carrion but most of them have a sweeter smell and believe it or not, they produce heat in the flower and that heat and the scent that they produce attracts beetles. and if you look at our big bull bay magnolia or southern magnolia those flowers the first day there the first day you see them pop open, they're only open that much right at night the first night they'll open up like this… beetles, come swarming in. and if you open one up when it's like that, you'll see it's full of beetles on the inside. and then what does it do at night it closes up and traps them. and it traps those beetles in there and hopefully they've been to other flowers too and picked up some pollen and the pollen all sheds off the first night and the stigmas become receptive to the pollen that's been carried into the flower with the trapped beetles and then in the morning the flower opens up and it opens up wide. and the stigmas become inactive and at the end of the day what happens? all the petals fall off and you're left with what we call an aggregate of follicles as a fruit.

Q: Do the beetles croak?

A: No, no, it releases them. It wants them to go away and go to another flower.

Audience:  It's a one-night stand!

A: It's a one-night stand, absolutely that's what it is. Isn't that amazing? And we've only recently started to figure out what the chemical cues are to attract the beetles and the fact that almost all magnolia flowers because they flower early in the spring, they produce heat to keep their beetles nice and cozy during the night. It actually attracts them into the into the flower.

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