 Okay, I think it's time to go, and so today we're going to be looking at seed plants. So last time we looked at some of the land plant groups, introduction of the land plants, and you saw some of the various innovations of land plants to living in a non-aquatic environment from which land plants emerged. On the bryophytes, like the mosses and the liverworts, hornworts, we had desiccation-resistant imidophytes, the dominant phase of that group of organisms, and also desiccation-resistant spores. And then we looked at the vascular plants, which as the name implies have this extensive conducting tissue associated with the presence of roots and a thick cuticle or waxy covering around the dominant plant body, the sporophyte, in those, in the vascular plant groups. But remember with the lycophytes in the ferns, which are the only vascular plants we've seen so far, these free-sporring vascular plants, there's a vulnerability there, at least a limitation, in that we have to have free-standing water for fertilization because there's still free-swimming sperm that have to swim to the archegonium through the open environment. So that limits the distribution of those plants to some extent, at least with regard to those that engage in sexual reproduction. I think I can just move this up a bit. Is that better? Okay, so today we're going to be looking at seed plants, which take innovations to land to kind of a new level in the sense that these completely shelter their gametified generations from the environment. There's no longer a need for free-standing water for fertilization. And they also shelter and nourish the young sporophyte generation as well to an extent that we haven't seen before. So seed plants have been tremendously successful. There's far more seed plant diversity than diversity of all other land plants combined. And we'll be looking at the two major groups of seed plants today, getting through the gymnast berms today, which are actually fairly low diversity compared to the flowering plants, which are the angiosperms, which taken together far more diverse than all the other land plants. Okay, so as it turns out, the seed plants are a monophyletic group. There's little doubt about that from the fossil record and molecular data. So it appears that the seed evolved only once. And concomitant with the evolution of the seed was the evolution of pollen. So it's really pollen and the seed that go together here that result in this sheltering nourishment of the gametophyte generation that I mentioned. And it looks like the earliest seeds came in during this period when we had those swamp forests that I mentioned at the end of last lecture where we had low-lying terrain and extensive fossilization that comprises our coal deposits today that were mostly likeophytes and ferns and relatives, but there were some seed plants especially coming in near the end of that time. And after that time, we have a period of extensive mountain building and cooler, drier climate that seems to have favored diversification of the seed plants, which as I mentioned, they don't need freestanding water for reproduction. They have some additional features that make them well adapted to land. And the current phylogenetic understanding is that we have a basal split here between the flowering plants and the so-called gymnast sperms, which I'll talk about in a minute. That's a little bit shaky based on the molecular data. It looks like there are five major groups of seed plants. Four of the five are in the gymnast sperms and their relationships to one another and to the angiosperms is a bit uncertain, but the data that are in hand are at least consistent with this kind of relationship that perhaps all of our modern gymnast sperms are equally closely related to the angiosperms. So that's the way we're going to present it. That's the way the book has it. But just be aware that it's not the most bulletproof finding, although the monophily of the angiosperms is well-established. Okay. So the gymnast sperms we're going to look at first, and this is a group of only less than a thousand species. So it's far less than 1% of the diversity we see in the flowering plants. And it's actually less than 10% of the diversity that we see in the ferns. So modern gymnast sperm diversity is actually fairly limited, but they can be ecologically dominant in some environmental situations, especially the conifers, the cone-bearing trees, as you're no doubt aware. And gymnast sperms are woody plants. Our modern gymnast sperms are woody. And their seeds are usually born in cones. And these cones are really distinctive, and you no doubt have seen pine cones, conifer cones. They're often woody cones, persistent cones that are pretty obvious in the environment. The seeds, though, are not enclosed in an ovary. The seeds are enclosed in a cone, but when that cone opens, the seed is exposed. There's no ovary around that individual, around a group of seeds. And the name gymnast sperm literally means naked seeds. In the flowering plants we have an ovary that surrounds and protects, and in some cases helps to disperse the seeds, and we'll get to that later. But the name is based on the absence of this ovary. All right, so three of the four major gymnast sperm clades have very low diversity today. There's less than 150 species in each one of these three major groups here. And even though these aren't very diverse, they're ancient, and they show some really interesting ecology and morphology. They're really cool plants, so it's worth talking about them. Now the most diverse are the cycads. The cycadophita, representative of which is shown here. And in this previous slide, there's an even nicer one here. And this may look like a palm tree to you, and in fact, horticulturalists that love palms, which are flowering plants, that have lily-like flowers, also tend to collect cycads, which are gymnast sperms, they're not flowering plants. And you can see that that doesn't look like a flower, that's a big woody cone. But they do have an unbranched trunk that's cloaked with the persistent leaf bases of leaves that have been shed, just like in a palm tree. And they also have their leaves all up at the summit of the stem that are ever green and compound, looks very much like a palm in all those respects, except reproductively, they're totally different. And these produce the largest cones of any land plant. Cycad cones can get huge, and up to like 100 pounds or so, some of them in some species. The individual plants produce either seed or pollen, not both. Although they've been known to undergo sex changes due to some sort of stress. That's not extremely well documented, but it's not completely apocryphal. They do seem to have occasional instances where the sex will change during the life, but that's unusual. And anyways, these are tropical or subtropical plants. And today they're found in small pockets around the tropics and subtropics. We actually have a native species in Florida. That's all we have in North America, or at least in North American, North of Mexico. But they're highly endangered. They're really sought after. They grow slowly. They're collected feverishly for, in part, an illegal trade. Because the rarer they get, the more valuable they get. They grow so slowly, people don't want to grow them from seed. So they're harvested, mature in the wild. And some of them are extinct in the wild, and quite a few of them are endangered. One interesting note, these are the only gymnast berms that are insect pollinated. So they may have evolved insect pollination 100 million years before the angiosperms, the flowering plants that are so famous for animal pollination. But it's only fairly recently that their pollination has been well documented. The other gymnast berms are wind pollinated. So they have a pretty different reproductive biology in that way. Okay, so that's the cycads, like 180 species, less than 200 species today. But they're really diverse back in the Mesozoic, back in the age of dinosaurs. And if you look at a typical dinosaur diorama, like at the Smithsonian, the dinosaurs are walking around with all these cycads around them. They were a pretty dominant plant back at that time, especially in the Jurassic. The Nita fights are a more obscure group. You probably haven't heard of those. They aren't so widely cultivated. There's fewer than 100 species of these. There are only three genera. And vegetatively, they don't look anything like one another, really. I mean, they have some technical characters that they share vegetatively. The most remarkable one is this thing called well-witchia that I'll just mention. It's not particularly important, but it only produces two foliage leaves in its entire life. And these just keep getting bigger and bigger, and they split, become wider and longer. And the whole thing at maturity looks sort of like a stranded octopus. Out on the deserts of Namibia, it's only known from these extremely dry deserts in Africa. And Darwin called it the platypus of the plant kingdom because of its bizarre biology. It doesn't look very much like our native aphedras here, which we have in California, out in the desert, as well as in other parts of the deserts of North America and Asia. This is a more diverse group. There's only one species of this. There's quite a few species of aphedra. And interestingly, these are the source of the stimulant aphedrine. You've probably heard of pseudephedrine, a pseudephed, active ingredient of pseudephed. Stimulant decongestant, actually raw material for making methamphetamine, as well. But this is an important medicinal plant. And there's another genus, Neatum, not shown here, which is the basis for the name Neetafida that's a tropical vine. So they look really different vegetatively and ecologically, but they share some interesting reproductive features that are unique to them. They have very small cones with unusual morphology. And finally, the ginkgo, of which there's only one species, ginkgo biloba. This is an Asian tree that used to be a diverse group back in the Mesozoic, based on the fossil record. But now there's only this one species left, and there's not been more than one species ever found in modern times. It's never been documented from the wild. It's only known from cultivation. And its history's been lost in terms of where it originally, but it's presumably of Chinese origin. And it has these weird, fan-shaped leaves you can see here. And it doesn't have cones. The seeds are born on stalks like this. Naked seeds with no cone. And they actually have an embryo inside that's really delicious and nutritious. I've eaten them. They're really great and sought after. But this external layer is extremely foul. It smells like dog feces or rancid butter when it's ripe. If you walk through the Grinnell Grove just west of VLSB, you can smell these. We have a seed producing plant. And like the cycads, it's pollen producing plants and seed producing plants, but plants don't produce seed and pollen. And when these seeds are ripe, you can smell it all over the Grinnell Grove. It smells like a kennel, really bad. But if you clean off the outside and break open the seed and get out the embryo, it's really a great edible. The leaves actually have an extract that is taken from them that's used to improve circulation and especially useful in, well, at least putatively, stroke victims to improve brain circulation. So Ginkgo is a minute group at this point, but it's evolutionarily and economically important. Okay, so the fourth major group of gymnisperms are the conifers, literally the cone-bearing even though other gymnisperms have cones. Conifers are the most conspicuous group. They're about 600 to 800 species worldwide except in Antarctica where they used to occur prehistorically. And they can be dominant in higher latitudes and altitudes especially, so you get up into montane situations, up into the mountains. You get up into higher latitudes, up in subpolar regions, and they become the dominant trees in many places. And of course, they're a crucial source of lumber worldwide. They produce really high quality wood. And in part, that's due to the fact that they have fairly decay and insect-resistant wood. So they have some interesting secondary chemistry that they produce, extensive resins, for example, and many of them that make them decay and insect-resistant. And this contributes to their long lives and the size that they can reach. They produce a lot of wood, and the wood's pretty resistant in many cases. So the very oldest known non-clonal organism on earth, and this is a little debatable because I've talked about those vestidium icetes that might be, their sizes haven't been as well documented, or their ages haven't been as well documented as the conifers, which you can core and count the tree rings and actually get a precise age. These are at least arguably the oldest known non-clonal organisms. These are bristlecone pines. And we get the bristlecone pines up in the white mountains of eastern California, just east of the Sierra Nevada, and in the high ranges of the Mojave Desert. These trees can reach ages up to about 5,000 years, and they grow in these very high elevations, sub-alpine situations on Dolomite, which is a really harsh soil. So they're in a really stressful environment, and they grow very slowly, and they live a long time. The oldest known individual was closer to 6,000 years old, but a forester who got frustrated trying to core it and get the age of it, took a chainsaw to it, and after he cut it down and killed it, he counted the rings and realized that it was much older than any of the previously dated specimens, and he became an incident pariah among all of the botanical and environmental and forestry communities for having cut the tree down. That's in eastern Nevada and Great Basin National Park. The biggest of all non-clonal organisms are the giant sequoias of California. They're endemic to California, so we have these here as well, and only here on the west side. You probably may have seen them in Yosemite or Kings Canyon or Sequoia National Parks, and they form small groves, but the trees are huge, and the mass of an individual tree here can get up to the equivalent of about 24 blue whales, which are the largest animal, and also roughly about the mass of about 40,000 people. That puts it in perspective that these are pretty big plants. As far as height goes, the tallest known, or I should say one of the tallest plants on earth, arguably the tallest are the coast redwoods, that are not quite endemic to California. They get into southern Oregon, but nearly restricted to California, where we find the tallest of these trees. A lot of really superlatives about conifers here that one can point to, though the changes in the gymnosperm life cycle that are really significant that I'd like to focus on in terms of comparing these to the land plants we've been talking about, as we see a major increase in the size and dominance of the sporophyte generation compared to anything we've seen before. This is true for seed plants in general, but we're focusing on gymnosperms first here. Remember in bryophytes, the sporophyte generation is basically a parasite on the gametified generation, and it's pretty ephemeral, it doesn't last too long. It's basically just a sporangium where meiosis occurs, and in mosses there's a stalk there, but it's just about as minimal as it can be. Whereas in a fern or lycophyte, we have a dominant sporophyte generation, but these plants tend not to be particularly large. Some ferns, tree ferns can get up to several meters in height, but they pale by comparison to the gymnosperms, which as we mentioned include the largest known organisms on earth. So there's an increase in the size and dominance of the sporophyte. The wood anatomy, the stem anatomy of gymnosperms is pretty special, and we'll get to anatomy later, but that in part accounts for that. Whereas on the other hand, the gametified generation is reducing through this series. So in the bryophytes, the gametophyte was dominant and was the photosynthetic organism, the primary photosynthetic organism in the life cycle. But they don't get very big, I mean we're talking about maybe 15 centimeters in height, up to two meters maybe, definitely up to two meters in some mosses. In the free sporing vascular plants like lycophytes and ferns, those two groups in particular, which are the free sporing vascular plants, the gametified generation is highly reduced compared to what we see in the bryophytes. And at best it's a photosynthetic organism of just a very small size, or it could be a subterranean organism living underground in association with mycorrhizal fungi, but or it could be living completely inside of the smore wall that it germinated from in the water ferns. But the reduction goes even further in the gametified of seed plants, and it's easiest to present this first in the gymnast berms, because you can see the homologies back to the gametophytes we've been talking about a little more easily than you can in the flowering plants, which have even more reduced gametophytes than the gymnast berms. So, gymnast berm gametophytes look like this. So, all of the seed plants descend from a heterosporous ancestor, so we have an origin of heterospory in this particular lineage that's separate from heterospory we see in some of the lycophytes and some of the ferns. All of the seed plants are heterosporous, and what that really boils down to is that they all have unisexual gametophytes. So, there's a male gametophyte that produces sperm, and there's a female gametophyte that produces eggs. All the seed plants show that, and these different types of gametophytes germinate from different types of spores produced by their parents sporophyte, thus their heterosporous, and so the male gametophyte is basically pollen, and at maturity in a pine it looks like this. There's not much to this, not very many cells involved here, basically you can see the old spore wall here, the male gametophyte develops within the spore wall, undergoes mitosis in there to produce a few vegetative cells, you can see those up here, and when it lands on the ovule, which is the immature seed where the female gametophyte lives inside, only then does it actually emerge from the spore wall that it germinated from, and it forms a pollen tube, and you can see the pollen tube here that has a tube nucleus that mediates its growth, and here you can see a couple of sperm cells, only one of which will actually be effective in fertilizing the egg of the female gametophyte. So the male gametophyte is really a reduced organism, but it doesn't release sperm directly into the environment, it doesn't have sperm that are released until this pollen grain is in contact with the ovule where the female gametophyte lives, and then it forms this pollen tube to deliver the sperm to the archegonium, the female gametangium where the egg resides. So there's a sheltering of this male gametophyte within the spore wall until it's actually in contact with the tissues of the ovule. Now the ovule is basically the immature seed, so that's just a name we give to an immature seed is an ovule, and the ovule basically consists of a tissue around the megasporangium, and we'll get to this in more detail in a minute, but from that megasporangium we have one megaspore that ultimately forms from which germinates the female gametophyte. Here you can see a female gametophyte of a pine. The seed coat at maturity here is shown, the seed's been broken open, and this is the female gametophyte. So if you've had pine nuts before, you're basically eating the female gametophyte, and the embryo that's inside the female gametophyte, which you can't see here because it's embedded inside the tissues of that female gametophyte. Of course this is after fertilization and zygote formation, the embryo develops from that zygote, and the embryo feeds on the tissues of the female gametophyte, and we'll look at some images of this in a second. Are there questions so far about this? Any questions about this? Okay, so the life cycle of a pine, just going to show it in terms of, well first of all, you've probably, if you, you know, nobody here was born yesterday, you've probably seen pine cones, conifer cones, this is what we tend to think of as a conifer cone or a pine cone in this case, but this is just the seed cone where the seeds are produced. These are the pollen cones, and gymnast berms produce their, their seed and their pollen in separate cones. The cones are usually born on the same individual sporophyte, they produce both types of cones, but in some cases they're not. There are some conifers that produce seed cones on some plants and pollen cones on others, and I mentioned ginko and cycads outside the conifers, but gymnast berms that produce their seed cones and pollen cones on separate plants, but in any case, the micro sporangia, the sporangia that produce the micro spores that germinate to become pollen, the male gametophyte, those are born in pollen cones, and the ovules which contain the female gametophyte are in, are in the seed cones. Okay? Everybody clear on that? So, here you can see a seed cone in early development, you've probably seen these if you looked at closely at a pine before, and this is after the seeds have been released. That period from the initial formation of the seed cone until it releases seeds is a period of over two years. Just the period between pollination when the pollen lands on the ovule and the time when it grows its pollen tube down to fertilize the egg, that takes over one year. So, this whole process is very slow in conifers and gymnast berms compared to what it is in flowering plants. The whole reproductive period is a fairly slow period. So, here's the life cycle shown with, and the details are sort of lost in these tiny drawings here. So, I'm just going to mention some of the highlights and then we'll go to a close up view. So, here you can see the mature sporefite pine tree in the case of this pine life cycle. And again, we have separate cones that produce the mega sporangia and separate cone, a different kind of cone that produces the micro sporangia. So, in those two different kinds of sporangia, we have meiosis going on to produce micro spores and mega spores on this sporefite. And those micro spores then germinate to become pollen grains inside the pollen cone, micro sporangia. And in the seed cone, we have the mega spore germinate to become mega gametophyte. And the important thing here is that the mega gametophyte never leaves the mega sporangium. So, you think of a sporangium, you know, the sac that produces spores is something that eventually breaks open and releases spores. That never happens in a seed plant. Seed plant produces one cell in its mega sporangium that undergoes meiosis. Just one cell undergoes meiosis. Of course, that gives you four products of meiosis. Only one of those products is actually functional. The other three die. So, one spore germinates to produce a mega gametophyte. And it makes sense that the ovule can only contain one mega gametophyte. There's not enough resources for more than one female gametophyte. Mega gametophyte and female gametophyte means the same thing. If you want to equate mega with female and micro with male, that's perfectly right. That never is conflict. There's no problem with that. So, the female gametophyte, one female gametophyte develops inside the mega sporangium, which is contained within the ovule and the immature seed. And eventually we have pollination, which is by wind. As I mentioned in conifers, wind carries the pollen grain to the ovule. Of course, a lot of pollen is lost. It doesn't make it to an ovule. Huge amounts of pollen have to be produced to get a pollen grain successfully to an ovule. But ones that make it there then can grow their pollen tubes down. There's an opening in the end of the ovule at the micro pylorin, which is where the arcagonia are closest to. And the pollen enters the pollen chamber and grows its pollen tube down to the arcagonia and where the egg is. And then here's the female gametophyte taken out of the, with removing of the immature seed coat, the integument. And this is after zygote formation. You might have multiple arcagonia here that are fertilized, but only one of them typically will be successful in producing embryo. And what you can see here is the developing embryo, this is where it was originally formed and it's thrust into the tissues of the gametophyte by these suspensors. It's embedded within the gametophyte and it eats up the tissues of the gametophyte as it develops. And finally we have the seed matures and basically typically this is a wind dispersed seed that might have some innovations like a wing that helps it disperse by wind. And finally it'll reach a side and it can stay in a dormant state for some period of time potentially. That's one of the beauties of being a seed plant is you have a lot of resources here and the embryo can go into a state of dormancy and persist for a long time until the environment's favorable for germination. And then the embryo eventually then will undergo germination and it will consume the remaining tissues of the gametophyte, the female gametophyte, as it emerges and sets up a root system and a chute system. So it gets a head start with some of the reserves inside the seed which is another advantage that seed plants have and eventually becomes a new sporophyte. So no need for freestanding water, maximal protection of the female gametophyte and the male gametophyte, well a lot of them are lost but they at least develop within the spore wall until they're in the protective chamber of the ovule. And then we have the nourishment of the embryo generation as it's getting established, or the next sporophyte generation as it's getting established. So there's a lot of nourishment protection of vulnerable stages of the life cycle both gametophyte and young sporophyte in the gymnast perms. Okay, so now the details of what's actually going on here just to put it in the perspective of these other life cycles we've talked, these other alternations of generations. So here again is an immature seed, this is an unfertilized ovule and then a fertilized ovule here and finally a mature seed over here of a gymnast sperm. So this structure here is the megaspirangium. So an ovule is basically in its earliest stage is just a megaspirangium, an immature seed is a megaspirangium surrounded by what's called integument which is an accessory structure of unknown homology. So this becomes the seed coat and there's a lot of uncertainty about what it represents in terms of homologous, is it a bract or is it a set of branches that sealed around the megaspirangium in an evolutionary sense. There's some uncertainty about that but basically we just have a protected megaspirangium that constitutes the immature seed. And as I mentioned only one of the four products of meiosis is functional, the megaspore here, the other products aren't shown and that germinates then to become the mega gametophyte which is all this kind of orange tissue here and you can see the spore wall here of the megaspore and there's the spore wall of the megaspore there so the female gametophyte doesn't leave the confines of the spore wall and the megaspirangium of course is basically encompassing that spore wall as well. It doesn't leave the megaspirangium either as I mentioned and eventually of course the pollen makes it there by wind enters the pollination chamber through this opening in the end of the immature seed and then the pollen tube grows down into the archagonium and releases the sperm here and then as I mentioned this is after the zygote is formed as it develops it's thrust into the center of the female gametophyte by those suspensors and here you can see now in maturity an embryo that has embryonic leaves and an embryonic root it's all set to go but it's in a quiescent or resting stage and it has all the female gametophyte around here to nourish it as it germinates later and the seed coat is hardened now and it's sealed around the tip here so it's not open and exposed to the environment and now the whole thing will be shed so basically rather than releasing the spore we're releasing three generations of tissue here by the time it's released we have three generations of tissue in a in a gymnasperm seed so the outermost layer of tissue the seed coat is from the parent spore fight that produced the ovule in the first place that diploid parent spore fight the tree the gametophyte generation is completely contained here as well the female gametophyte that's haploid tissue here and then we have the next spore fight generation diploid organism forming here so there are three generations of tissue to yeah correct oh so these are just recapitulating some of the general points here but I mean this kind of shows the maximal protection and nurturing of multiple generations here by this parent spore fight that produced the ovule so that's some of the details of the gymnasperm life cycle anyone have questions yeah Brad yeah exactly the microspores are shed from the microsparangium the pollen grains represent basically the microspore leaving the microsparangium the pollen sacks of the of the the seed or the pollen cone and they're carried by wind so the pollen grain is the microspores are released from the microsparangium and they undergo their final development once they're in contact with the ovule yeah the mega good question the mega sporangium is gradually consumed by the female gametophyte there's it doesn't really show it here but actually in reality there's mega sporangial tissue that persists down at this end at this part of the ovule and the pollen tube as it grows down is actually parasitizing that mega sporangial tissue it actually grows host orally as it's called it's it's it's it's growing down in and it gets its energy by consuming that remaining mega sporangial tissue here as it grows down so that's a good point yeah yeah well the the ovule is basically the immature seed right so there's a point at which it's the seed the term seed is usually reserved for the mature state but it's easiest to think of ovule as an immature seed the problem with the term ovule is people confuse it with the term ovary and if you do that that's going to completely blow your conception of what's going on here because the ovary has nothing to do with the ovule I mean ovules are contained within ovaries and flowering plants as we'll talk about but it's a completely different structure just want to that's one reason why I like to call it an immature seed is so people don't get it confused with an ovary but the ovule is just the immature seed I call it an immature male gametophyte because it's already undergone some mitotic cell divisions at that point and it's only so it completes part of its development prior to being shed from the micro sporangium the pollen sac and then it finishes its development once it reaches the ovule yeah so it's an immature male gametophyte but it's completely contained within the micro spore wall at that time yeah the micro pile is just the opening in the ovule which provides an entrance for the pollen grain in some gymnasperms there's a pollination droplet right there a sticky droplet that the pollen grain will adhere to and then as it dries out it'll retract and pull the pollen grain into the pollination chamber yeah the micropiler end is the entrance of the pollen end and this end is called the chalazal end that name we don't need to know that I mean the micro pile term is not important either it's just the term we use for that end of the seed or the immature the immature seed or ovule okay so some conifers have pretty bizarre cones that don't look like our normal conception of a conifer cone for example junipers here have fleshy cones you're familiar with juniper berries that are used to flavor gin that's actually a cone it has comprised of a number of cone scales all fused together and fleshy and these are typically bird dispersed some other conifers don't even really have a cone anymore or it's just a vestige of what it and it's clearly a case of reduction because these are nested phylogenetically among taxa that had columns that are well developed taxes the U is a great example cephalotaxis is another these genera are not important to remember but in this case the actual seed is surrounded by fleshy tissue again often dispersed by birds potentially other animals as well so conifers even though they often disperse their seeds by wind they some of them have have evolved features that are that promote dispersal by animals as well these ones are not so readily recognizable as conifers to most of us alright so any last questions about gymnasperms before we move on to angiosperms alright the angiosperms are the flowering plants and the word angiosperm just means vessel seed and that name refer vessel seed just refers to the fact that in angiosperms the seeds are contained within a so-called vessel which really is the ovary so we'll talk about what an ovary is later but there's a structure around the seeds that's novel for this group and it diagnoses the angiosperms as a monophyletic group and they're definitely a good clade based on every bit of data we have so the angiosperm lineage here based on our tree shows it coming back all the way back to when the gymnasperms diverged here on the carboniferous but that's lost if there were angiosperms back here there are no fossils we don't start picking up fossils until about 130 million years ago we'll talk about this later but the angiosperm fossil record has provoked a lot of controversy and trying to figure out what the earliest angiosperm was is sort of the holy grail of botany as far as you know if you figure that out you know you've you really made the big time as a botanist there's a lot of controversy about it of course if the stakes are that high anyways the angiosperms are an exceedingly diverse group so the estimates vary widely in terms of how many angiosperm species there might be on earth but we're talking about at least 300,000 species and that's way in excess of all the other land plants combined at least as far as we know and that diversity is expressed in a lot of ways I mean you can see some flowering flower diversity here and there's also tremendous fruit diversity we'll talk about really remarkable these are found worldwide on all continents including Antarctica a super successful group but not a super old fossil record and one of the innovations of the flowering plants that may have been important to its success is the flower and in particular as I mentioned the ovary the carp will talk about in a minute so basically to understand what a flower is it's just a simple cone we talked about cones cones are structures that bear sporangia and in the case of seed plants bear pollen and seed flowers are simple cones or strobeli that bear pollen and seed and they're made up of a few separate types of appendages here there are four general types of appendages on the cone that make up the simple cone or flower of a flowering plant two of these appendages are sterile the steeples and the petals and the other two are fertile, the stamens and the carpels and there's some wonderful developmental genetic work that's focused on understanding the genetic basis for production of these different sets of appendages that's really pretty well worked out at this point that we won't get into but there's a lot of active work on the development and evolution of the flower so this is a little bit, this is clearly a pretty idealized drawing here because we're showing pretty long inner nodes and the inner node is just a stem segment between two nodes, a node is just a point on a stem where we have leaves produced and so these are leaf homologs, the sepals, the petals, the stamens and the carpels pretty clearly based on a lot of lines of evidence, these represent modified leaves and there's generally four or more at a node of each one of these types of appendages in a typical flower so here's what a fossil looks like, this is a particular gem of sperm from back in the Cretaceous particular fossil gem of sperm that gets back to almost the beginning of the fossil record in flowering plants, what it looked like this is an artist's reconstruction of this fossil and you can see stamens down here and carpels up here those are the two and you can see that this is on a pretty elongated axis with inner nodes visible between the appendages that's pretty unusual, we don't see that in modern flowering plants much although this is not the most recent common ancestor of all living flowering plants, this was toted as the missing link or the most ancestral flowering plant but it turned out the stratigraphy was wrong and it's actually probably pretty closely related to modern water lilies but it nicely shows how these floral appendages are born essentially at nodes whereas when we look at a sort of typical flower which this is a cartoon of, those inner nodes are no longer visible they're extremely short and these four sets of appendages lie directly on top of one another with the outermost appendages being the sepals again and the sepals have an important function they often look somewhat leaf like, they're often green and they're sealed around the rest of the flower when it's in bud so they can perform an important protective function of the rest of the flower which contains the goods, the reproductive parts covered with hairs or glands that repel herbivores and protect the flower to some extent even after it opens they can protect the flower from things walking up the peduncle the petals are not always present, they've been lost in a number of groups especially where we have wind pollination ancestrally we appear to have insect pollination, animal pollination in flowering plants though and we have showy parts in the majority of flowering plants and these are typically the petals so the petals form an advertisement they perform an advertisement function to potential animal pollinators so they're commonly distinctively colored or have patterning on them that basically serves as a flag to pollinators that hey I'm over here, come on over and we'll get a reward and as that occurs the plant also gets a reward, it gets pollinated so there's this mutualism that has developed between pollinators and plants and one of the ways the plants attract the pollinators is with their petals. Okay so I think we're not going to, well I'll just show you this one last slide which is to make the point that understanding floral advertisement by petals requires considering the visual spectrum of the most important pollinators many of our plants are pollinated by bees as you're no doubt aware bees actually see shorter wavelength light than we can they see ultraviolet light and here you can see an ultraviolet image of the same species flowering head, you can see this bullseye pattern that we can't see with our naked eyes so it's often important to consider the pollinator's perspective when you're figuring out the exact advertisement. Okay so next time we'll talk more about flowering plant flowers and inflorescences