We get tons of questions about plants. What's the biggest one? The largest flower? Why do leaves change color in the winter? Sue from our education team digs up the answers to these and other queries in this Pulsar podcast brought to you by #MOSatHome. We ask questions submitted by listeners, so if you have a question you'd like us to ask an expert, send it to us at sciencequestions@mos.org.

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ERIC: From the Museum of Science in Boston, this is Pulsar, a podcast where we dig for answers to the visitor questions that grow on us. We've had many episodes covering the questions we receive about animals, but we are also asked about plant life fairly often. Joining me once again to answer your questions is Sue, who has been an educator at the Museum of Science for over 35 years. Sue, thanks for joining me again on Pulsar.

SUE: Great to be here.

ERIC: So I knew you'd be perfect for this episode, because our desks are really close to each other at the museum. I can't keep a cactus alive for, like, a week, and your desk is covered in green things.

SUE: Well, you know, I love talking about plants. And I will say you can let yourself off the hook. It's pretty challenging environment where we are in the Museum of Science to keep things alive.

ERIC: Well, I thought we'd start with some extremes, we always get asked on our live streams about the fastest and the oldest and the biggest things. So what is the largest plant?

SUE: The largest plant, well you know, it really depends on how you define it. There's a lot of ways of measuring biggest. Most scientists agree right now that the largest individual plant, although we'll have to wrap our heads around what individuality means in this case, is an Aspen Grove in Utah. So basically, it's a single tree that, through roots, and what they call the process of suckering, moving underground, and then starting new trees along the length of its roots, has formed this huge grove, it's about 108 acres. But basically, because the shoots came from one original plant, they all have the same DNA. So they are considered one individual. It's kind of like if you've ever tried to reproduce a plant, you know, with a cutting from your philodendron. So when you take that philodendron rooted in water, and then put it in a pot, believe it or not, that philodendron is genetically identical to the original plant. And it's considered the same individual. It's essentially a clone.

ERIC: So it might look like a whole bunch of trees, but really, it's one organism all connected by roots covering 100 acres, right?

SUE: Isn't that crazy? A lot of people will say, you know, redwoods and sequoias. And definitely if you're going with an individual plant, as we think of one like a tree, they are some of the biggest trees on the planet. The ones that are alive today maybe are not as big as they were in the past, some of the real giants may have fallen before we ever got a chance to measure them. But typically, both types of tree can exceed 300 feet, and over 20 foot diameters for all of them. So they're massive.

ERIC: That's enormous. I mean, if you planted one on Boston Common, it would become part of the skyline. That's as tall as some of the skyscrapers we have downtown.

SUE: And they would look almost as tall as the Bunker Hill monument. Can you imagine a whole bunch of trees that size?

ERIC: That would be kind of awesome. And another extreme question we got was, what is the largest flower?

SUE: This is this is one of my favorites, because it's such a weird flower. So it's called Rafflesia. And it grows in in Indonesian rain forest. And basically, if you saw it, it looks almost like kind of a cartoon version of a kid's drawing of a flower. So it's kind of flat, puffy pancakey looking, with big funny little round petals around the edges, kind of brown and white speckled with a sort of center hole that has a red on the inside. And its other name is Queen of the Parasites. It's a parasitic plant that grows on vines in the grape family. It can't really support itself on its own. But this flower is massive. It's about three feet across, and it has an unbelievable stench. So it produces a fragrance, but it smells like something died. And apparently the smell can travel quite a number of miles. And everybody might want to think about what type of pollinator are you trying to attract if you smell like rotting flesh, and you're right, it's flies. So the flies buzzed into that little center opening that's already kind of meat looking and meat smelling. And they get stuck in there for a little while, you know, kind of bumping around picking up pollen and then the flower kind of shrivels, they get out. And because flies don't have great brains, they fly right to the next one.

ERIC: I love that evolution in action. The stinkiest flowers attract the most flies and reproduce to make more stinky flowers. Now not all flowers are smelly. In fact, we associate most flowers with being attractive visually. And sometimes visitors want to know, why are flowers so brightly colored?

SUE: That's a great question. So some of the earliest flowers didn't have much color. They weren't very big, and maybe they were kind of pale whitish or a little yellow and a little green. But a lot of the earliest flowers were actually wind pollinated, so the pollen in those flowers would just blow on the wind to the next flower and pollinate it. But as pollinators evolve, like bees, butterflies and other things, flowers began to develop color. And bees and butterflies and a lot of other insects can see really well in color. Bees in particular can see blues and reds really well. They also can see polarized light and ultraviolet light. So flowers began to evolve these amazing colors along with great sense as well to attract insects. So those beautiful colors are really all about bringing pollinators to your flower so that you can distribute your pollen and reproduce.

ERIC: So kind of like an advertisement, hey, bugs! Come land on me for some nice food.

SUE: Yeah, and sometimes if you're looking at a flower that seems to be very attractive to bees, but it's kind of boring, like maybe a pale white or yellow, that they may actually have an ultraviolet marking. So you can hold a handheld ultraviolet light over one of those flowers. And sometimes you'll see little dots and lines and stripes that lead right into the center of the plant, where the pollen and the nectar are, just like landing lights at the airport.

ERIC: That's so cool that we can't even see it. It's like a secret communication from flower to bee that humans are totally oblivious to.

SUE: It is, plants are really sneaky. Super sneaky.

ERIC: Alright, so here's a question that's super common here at the museum because we're in New England, and we get that famous autumn foliage. Why do leaves fall off of trees when it gets cold?

SUE: That's a really great question as well. So this happens sort of on a regular timing schedule, mostly in the northern and extreme southern hemisphere. If you went to plants in the tropical rain forests that have these so-called deciduous or easily shed leaves, it kind of just happens at random times of the year, because the daylength doesn't change very much. So that big leaf drop that we get here in New England in the fall is timed to day length, usually right around when it's equal day or equal night. And then past that, when the length of the night actually gets longer. Certain receptors in the plants and trees pick up the shortening days and they begin to change their physiology and response. So to protect themselves over the winter, what they want to do is dump all those leaves which can be easily damaged by cold and oftentimes would drain out moisture in the form of evaporation. So they begin to do things like seal up the leaves from the twigs, eventually, they seal off and form a little, almost little scab over that spot and the leaf is totally cut off from the supply of nutrients from the branch and the leaves will eventually drop. Now they changed the beautiful colors because a lot of the colors are there already, just masked by the green of chlorophyll while the leaves are alive. But the minute the chlorophyll starts to die off, we start to see particularly the yellows and the oranges. And then as the temperature starts to drop, for example, a lot of maples like sugar maples, that ups the production of the sugars that are stored in the leaves, and that stimulates the production of another set of colors. The bright reds that we often see in the fall as all the leaves fall off. So of course, conifers are different from deciduous trees that drop their leaves, they keep their needles all winter long. And they can do this because they're very well adapted for the cold. They have a waxy covering on the needles that protects them from the evaporation of water that might cause the leaves to have frostbite, and those green leaves can actually continue photosynthesizing over the winter, maybe at a slightly lower rate because of the lower temperatures, but they're still pretty active during the winter.

ERIC: I do love when you see that different adaptations to the same environment to different trees growing next to each other in a place where it's freezing cold. For a few months of the year, one evolves a way to drop its leaves and seal off its moisture. The other one evolves leaves covered in wax that can survive those conditions. It's completely different. It's amazing.

SUE: It's different solutions to the same problem. And plants are amazingly adaptive when you think they evolved on a planet that was a lot more hostile than the one we experience today. And they are in no small part responsible for making it nice for us. But they have had to have strategies that allow them to survive some really huge environmental changes. And so there's a huge variety of ways they adapt to changing conditions, you know they are portrayed is just something that sedentry and nonreactive and unable to interact with their environment. But scientists are learning more every year about the communication that goes on both underground between roots and through the air when chemicals are released from the leaves of trees. They're talking to each other.

ERIC: Well, hopefully our listeners will have something to think about next time they go for a walk by all the plants in their neighborhood. Sue, thank you so much for answering our questions today.

SUE: My pleasure.

ERIC: You can come to the Museum of Science and check out our Garden Walk and Insect Zoo and send your plant questions to sciencequestions@mos.org. Until next time, keep asking questions.

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