[MUSIC] So far we have been dealing with the origin of the flowering plants. But once the flowering plants had arisen, the subsequent evolution and diversification took place very rapidly. In the fossil record we can find eudicots, the largest present group of flower and plants just ten million years after the oldest known angiosperm pollen. It is this subsequent diversification we will explore now back in the Botanical Garden. Today flowering plant diversity is astonishing. Just think about such a simple thing as size. From the largest broad-leaved trees being up to 100 meters high to this tiny little duckweed, where each little green speck on the surface of the water is an entire plant. And each of these little plants can make its own flower. From these, the world's smallest flowering plants, take a look at the picture of the world's largest flower, the Rafflesia, that can be more than 1 meter in diameter. As I spoke about in the first presentation, we have some pretty good ideas about how the first or early flowers looked. So we can also describe trends in the development of flowers from the past until today. But please bear in mind that these trends that I will describe are not more than just trends. There are many many alternative pathways of development. The first flowers, as the Schisandra or Kadsura that you saw before did not have differentiated petals and sepals, or uniform floral leaves. But looking at the Paeony once again, we can see that the outer floral leaves have developed into the green sepals, which surround and protect the young flowering bud. And the inner floral leaves develop into the bright, showy petals, having a function of attracting pollinators to the flower. So, a specialization of the floral leaves has occurred. From the early flower with symmetrically arranged floral leaves, the advanced flowers often have reduced their planes of symmetry. They've become irregular. The Penstemon, as you can in the picture, is irregular. In this flower, you can clearly see that only by mirroring it around the central axis you get two similar images. This is also an adaptation to pollination, The flower attains a shape allowing just some pollinators to get in, leaving others out. All the flowers we have seen so far, also the Paeony, have the ancestral trait of being hypogynous. That is the pedals and sepals are located below the carpels in the central part of the flower. But in many evolutionary lineages, the position of the petals and the sepals has apparently changed to the top of the ovary. Look at this iris. In this plant, or this flower, we can clearly see the showy petals up here, but the ovary is not placed inside the petals as the other flowers we have seen, but below. I need to remove these scaly leaves, to reveal the ovary, which is located here. And on top of the ovary, exactly from this point, start the petals. So this flower is called epigynous. What has really happened is not an actual displacement of the petals and sepals from the bottom to the top of the ovary. But rather that the petals and sepals in the lower part have surrounded and grown together with the ovary. The general interpretation of why this happened is that the ovary becomes better protected because the ovary is now sheltered from the petals from pollinators visiting the flower, from this side. Just as a bonus information, I can show you how easy it often is to see from ripe fruits to see if they are from hypogynous or epigynous flowers. Here is a tomato and it is easy to see that the flower stalk and the withering sepals are sitting in the same end of the fruit, so this is hypogynous. But if we look at an apple, you can see that the flower stalk is in one end of the fruit. And in the other end you see the remains of the withering sepals. So this is from an epigynous flower. A couple of other traits that have evolved relates to the stamens and carpels. In the first flowers, stamens were short and broad, more leaf-like. Now most flowers as the Paeony and the Penstemon have stamens, which are developed into long slender filaments and anthers, including the pollen sacks on top. Carpels were also rather short in early flowers, with the stigma placed just on top as we saw it in the Kadsura and also in the otherwise more derived Paeony flower. But in many modern flowers, the carpels have developed into a long, slender extension, the style, raising the stigma above the ovary. You can easily see it in the Penstemon. The development of both the filaments and the styles are also adaptations to pollination. Again, it can provide a better protection of the ovary, simply because it increases the distance from the pollinator to the ovary. But it may also position the pollen and stigma just right in respect to the pollinator. So in general flower evolution is closely, but not exclusively linked to pollination biology. The first flowering plants were most likely pollinated by insects such as beetles, but actually insect pollination is not restricted to the flowering plants. Insect pollination evolved earlier in the seed plants and some of the extant seed plants as the cycads and gnetophytes are actually insect-pollinated. But from the simple flowers, where insects like small beetles would just crawl around browsing for pollen, more and more specialized flowers evolved in close concert with specific pollinators. In many of these more specialized flowers, the reward to the insect is no longer pollen, but nectar produced by the flower. Some of the classic examples of highly specialized flowers are from the orchids, so let's go and have a look at some of them. Now we are in the orchid house, but only few plants are flowering right now. But that doesn't really matter, because many of the orchids really all look the same. The petals may have different sizes and shapes and colors. But roughly speaking, all orchid flowers are built in the same way. Try to look at this one. In this orchid flower from a Eulophia, we can actually much easier see than in the Penstemon before that orchids are regular with one plane of symmetry here. Orchids also have a very peculiar structure in the central part of the flower. You can see it in the middle of the flower, the gynostemium. This is this organ you can see here which is a fusion of carpels and stamens. You may also see in the orchid flower that it is a epigynous. The fruit is located here below the petals. It may look like a stalk, but actually it is the fruit, which in this species and many other orchids are just very, very thin. It's easier to see in another orchid and we have another one just here behind. This is a vanilla. You can see we have the flower and the much thicker fruit below the petals. This is what develops into a vanilla pod. Here we have some fruits that are even more ripe and it's easier to see that they actually are fruits. And finally when the fruits become ripened they start to get brown and almost fermented and you may be able to see some tiny black seeds coming out from the fruit. These are the vanilla seeds that we use as a spice. All these orchid flowers, their shapes and the variation in shapes are developed in very, very close concert with their pollinators. Orchids are usually pollinated by bees or moths. And many flowering plants in general are insect pollinated. But some are actually pollinated by vertebrates, mostly birds, but also smaller mammals. But let's go and take a look at some that are actually being pollinated by birds. Among the birds, you probably, first of all, think about hummingbirds, which are indeed the most common and important group of pollinating birds. This flower is a typical example of a flower being pollinated by birds. And, I have here, some other flowers that I have collected in the garden all of which are pollinated by birds. I think you can easily see that they have a number of traits in common. The flowers are often bright red because this wavelength is best seen by the pollinating birds. The flowers have a long tubular corolla fitting the long slender beak of the birds, and they produce ample amounts of nectar as a reward to the birds. Bird pollination has evolved from insect pollination, mostly from flowers being pollinated by bees. And some of these flowers are actually still so unspecific in terms of pollination that they can be pollinated by both bees and birds. Flowers that I have collected, are from several different plant families so they do not represent just one evolutionary lineage. Evolution from insect to bird pollination has occurred many times independently, probably dating back to the Cenozoic. The morphology of flowers which are pollinated by bats has evolved quite differently. As bats are nocturnal most bat-pollinated flowers have most likely evolved from flowers originally being pollinated by nocturnal insects, as moths. But there are also examples of bat- pollination having evolved from bird pollination. Bat-pollination is a relatively recent invention, probably dating back to the Mid-Cenozoic. The bat-pollinated flowers are usually pale or white, quite big and often very tough to withstand potential contact with the larger pollinator. They contain plenty of nectar as a reward to the bats, and they omit a smell to attract the animals. Typical examples of flowers that are bat-pollinated are from the African baobab tree, or the flowers of many columnar cacti. But also, bananas are pollinated by bats. But highly specialized flowers need not be large and attractive. Take a look at this fig. You may think it's a fruit, but if you do, you have actually been deceived. Let's see what happens if I cut it open. Inside the fig, you can see a lot of small structures, which you may think are seeds, but this is not the seeds. This is actually tiny, tiny, flowers, each single little pale white thing here. I can demonstrate how something like that has evolved. We have a species growing here below the table. It is called a Dorstenia. This is what it looks like, very, very peculiar. What you see here is actually, though it looks like leaf, a complete inflorescence, filled with a large, large number of the very, very small flowers. Try to imagine that we can take this inflorescence and fold it, and eventually end up with something that is completely cup-like, just with a tiny hole in the middle. Then we have developed a fig. In flowers like these tiny, hidden-away fig flowers, petals and sepals would be of no use. So as a consequence they have been very strongly reduced, or even lost completely. Other flowering plants have reduced or lost their petals and sepals as a consequence of dropping insect pollination entirely, but using either wind or water as a mechanism for pollination. Let's go and find some of those flowers. Wind pollination has evolved in several groups of flowering plants. Grasses is the largest group of wind pollinated plants. But also many forest trees common to the temperate climate, like birch, beech, and oak, are wind pollinated. What you see here are some catkins of male flowers from a walnut tree. Each flower is small and inconspicuous and it includes little else than stamens. So from the inflorescences like these hanging from the tree, large amount of pollen will be released. We can see similar traits in grass flowers. Here is a rice plant. And we can see it's large anthers hanging out from tiny, very reduced flowers. The stigmas are also relatively large, increasing the chance of catching pollen from the air. This, again, is, inflorescence composed of many flowers. Most grasses have smaller flowers than these, and it may be difficult to see their floral parts. But look at this Zea, a wild relative to corn. As grass flowers, these are almost gigantic. And again you see all the stamens hanging out and the exceptionally long stigmas. In this greenhouse, we have the opportunity to see water pollinated plants too. Most water plants solve the problem of pollination simply by placing their flowers above water and then use some sort of insect pollination. Just think about the waterlilies. But some use the current of the water for pollination, either on the surface or even below the surface. Vallisneria sends its flowers on long coiled stalks up to the surface. Vallisnerias are unisexual flowers, so these are the female flowers with the large stigmas. The male flowers are developed under water, but then they become detached from the plant, they float to the surface, and there they float around like little boats, which in the lucky case, bump into a female stigma. Unfortunately, I've not been able to find any right here. Surface pollination is by far the most common type of water pollination, but there are a few water plants that have managed to keep their pollination entirely below the surface. So far I have talked a lot about adaptations of the flowers to pollination. But this is, of course, not the only thing driving evolution. In the next video, I will talk about other factors, biotic and abiotic, that have influenced evolution of the flowering plants and how the flowering plants have influenced life on Earth. [MUSIC]
