[SOUND] [MUSIC] So Earth's tracheophytes, all right, so these are the first land plants that may have arisen in the early Silurian. And these would resemble kind of filamentous green algae, here are early tracheophytes. An early forest would not have appeared until the Devonian. So within Earth's tracheophytes, we have three different flora, and we're going to define those stages of Earth's flora, one, two, and three. So within flora one, our first type of plant that we'd like to introduce to you here. Maybe you've already seen these, these are your ferns. So this is a wonderful impression of a fern. And the technical term used to refer to ferns, is pteropsida, and that means true fern. And so these were most diverse in the Paleozoic, and have declined since then, definitely still around today. And they have notable spore pods on the back of the leaves there. I'd like to show you another example of a carbonized fern. And so you can see it has kind of this blackened area, and that's basically all the organic material has been pressurized into just kind of a black smudge, honestly, just the presence of carbon there. All right, moving on. Our next plant in flora one are the lycopods, and these are club mosses. Kind of a low growing plant that lacks seeds, but they do have notable leaf scars on their stems. But what's interesting to me, kind of my imagination I suppose, is that these lycopods actually grew to 30 meters high during the Paleozoic. So we actually had trees of these lycopods with these huge stems and these leaf scars. So, we do have evidence of that actually. All right, that's what we need evidence, right. And so, evidence of that is a specimen such as this, this is actually a smaller little example here, a smaller specimen. But you can actually see here kind of the cross hatching of this lepidodendron stem. So the term lepidodendron refers to a fossil of the stems, okay that's something to note, of the stems only of these club mosses that were successful during the Paleozoic. Okay, and something I want to kind of contrast this stem fossil to is the fossilization of the roots of this plant. So here we have a lovely, I would say a cast here, we have a cast. And what you can see here is you actually can see these root hairs, kind of the scars of the root hairs on this plant fossil, and the term stigmaria is the name that has been applied to the fossils of these roots of these club mosses, of these lycopods. And so that's an example of forum taxa. So forum taxa again, to reiterate, is just where you have a couple different types of fossils here that you find, and scientists actually have named them two different names expecting that they're two different organisms and later we put them together in kind of a model and we recognize that these are actually two different parts of the same organism. So, this is a great example of forum taxa, our lepidodendron and our stigmaria that both represent a lycopod in the Paleozoic. And one more thing we want to note about the lycopods, is that they were definitely dominant and just wildly successful during the Pennsylvanian, and the Pennsylvanian forest decomposition has resulted in those swamps, not only the forest but the swamps as well, and the decomposition of those organisms that comprises much of the world's coal, actually. So a lot of organic material there being fossilized and eventually pressurized into coal, which again, is a chemical fossil, right? Coal is a chemical fossil, just to review. Continuing on with Flora one, the next group of organisms or plants are the sphenopsids and these are your horsetails. So again, these horsetails grew to large sizes during the Paleozoic but definitely a little bit smaller organism that persists today. And these are characterized by leaves that radiate outward in whorls around the stem, and the whorls are kind of separated by these jointed stems. So we have a couple of great fossils here. Another example of forum taxa. So the leaves, of these sphenopsids were termed annularia. That's the name, that this particular organism was assigned when this fossil was discovered. So annularia here, and if you can imagine these leaves would be rotating outward in these whorls around the stems. The actual stems, we have some great fossils here, the stems of these sphenopsids were also fossilized, but they were named something different. They were identified as a different organism when they were first discovered, so the stems are termed calamites. So we have annularia and calamites, and those both comprise the aphenopsids. On the calamites fossil you can see really clearly where the whorls of leaves would have attached. And so you can see we kind of have these jointed stems going upward in the longitudinal direction and we actually see the scars where the leaves would have kind of projected around, would have radiated around. kind of interesting. The next group of plants in flora one are your seed ferns. So again, we're kind of contrasting to our pteridops, our true ferns. So the next group though, are seed ferns and so these aren't true ferns, they look like true ferns but they actually have seeds and not spores. And this group of ferns is actually extinct. The next stage in plant evolution is termed Flora two. This refers of the time period that was the mid-Permian to the mid-Cretaceous and refers to the organisms were successful during that time. So we'll start with our gymnast ferns. So gymnast fern refers to the idea of a naked seed, and they basically rely on wind to spread their pollen. Examples of gymnast ferns are conifers, cycads, junipers, and ginkgoes, kind of a beautiful group there. But they all rely on the wind to spread the pollen, so that's kind of a key factor with these gymnosperms. And something I should note about flora two is gymnosperms, they may have been more wildly successful during the min-Permian to the mid-Cretaceous, but they're obviously still around today. And so we can observe really great examples of these gymnosperms in the recent environment. The third group of Earth's tracheophytes is flora three. And this time period is from the mid-Cretaceous to the recent. And these were dominated by Angiosperms. These are flowering plants or seed plants, and that means there is the presence of a flower, a nut, or a seed. So angiosperms dominated kind of of Earth's flora from the mid-Cretaceous, on. Something interesting about angiosperms is that they rely on insects for pollination, so this is an example of co-evolution. And this particular example of co-evolution, where two species sort of evolve to benefit from one another is called mutualism, where both organisms are actually benefiting from that relationship. [MUSIC]
