Why Do Flowers Exist? (Gymnosperms & Angiosperms): Crash Course Botany #9

there's this plant called jewelweed also known as touch me not why you asked because when you touch its seed pods they have a habit of exploding the seed pods fooling the jewelweed seeds into the air to spread them far and wide and then there's the seeds of the Osiris plant which develop faster if they've been roughed up a little inside a bird's digestive system after that they tend to try and grow wherever the bird drops them foxtail seeds hitch a ride on animals fur maple tree fruits surf on the Wind oak tree fruits or acorns

Sprout where squirrels bury them are you sensing a pattern here the pattern is plants move they migrate and spread over the globe just not in the same ways that animals do no sometimes it is via those animals throughout land plants 500 million year long tenure on Earth they've devised a lot of clever ways to get around and when seeds flowers and fruit came onto the scene well that was a major plant moment hi I'm Alexis and this is Crash Course botany [Music] in the last episode we explored bryophytes and seedless vascular plants some of the

earliest plants to thrive on land and today we're looking at the evolution of the seed which came about 150 million years later and changed everything when gymnosperms or seed bearing plants appeared they opened up entirely new habitats and ecological opportunities for plants and then angiosperms which bear flowers and fruits came up with even more Innovations for protecting and spreading those seeds because of their evolutionary advantages these two types of plants dominate Earth's ecosystems shaping how virtually every other organism lives and interacts and they are by far the most common types of plants you're likely to

interact with in your daily life before gymnosperms plants could live on land but they needed a pretty wet environment because in their reproductive cycle a plant's sperm could only reach an egg by swimming but the evolution of pollen which coincided with the evolution of seeds meant seed plants were no longer dependent on water for reproduction that's because pollen which produces not only allergies but also plant sperm to travel by wind rather than water so plants were able to expand into habitats previously and accessible to them and all of this happened very gradually as new types

of plants built upon and tweaked what came before kind of like how newer phones have more powerful cameras or let you turn your face into a unicorn but they still have the same foundational features of older phones you still need the part that lets you make phone calls you see previously existing plants like ferns had produced spores or single cells crucial for the plant's reproduction these tiny cells grow in special structures on the leaves called sporangia and pro gymnosperms which evolved about 390 million years ago preceding gymnosperms still use spores to reproduce but we can

see from fossils that Pro gymnosperms started making two different types of sporangia when the pro gymnosperms evolved into the gymnosperms of about 70 million years later they specialized those two sporangia one produced little spores like their plants Elders had but the other produced one big Spore protected by a layer of tissue called the seed coat this structure as a whole sporangium plus Spore plus seed coat is called an ovule and when it grows up and matures it becomes a seed but let's unpack that there's the sporangium that makes little spores these become pollen with which

produces sperm and then there's the sporangium that makes a big Spore this Spore transforms into the next generation of the plant and then produces an egg when pollen lands on an ovule it sends its sperm down a little tube to fertilize the egg inside the ovule the fertilized egg grows into an embryo which will eventually become a baby plant and once it contains an embryo like this the ovule graduates into a seed the evolution of seeds created a huge Advantage because now embryos were protected and nurtured in their cozy seed coats this let them travel

safely and well fed as they were dispersed whether by bird or wind or explosion and that let these plants spread farther with more reproductive success than others had up to this point now there are a few different types of these seed bearing gymnosperms many of which are still around today cycods are one of the oldest gymnosperm groups they were around even before the dinosaurs but they grow very slowly and only in specific habitats so most species are considered endangered today then there are the gymnosperms you're likely to recognize conifers include trees like Pines Cedars first

and cypresses that make scale or needle-like leaves they're often adapted to harsh environments like freezing mountain tops or Barren deserts and there's a gymnosperm category you might know by scent the ginkgo these trees have been known to produce stinky seeds but they're widely grown in cities around the world because of their resistance to pollution the last of the gymnosperm groups to evolve were the Neato fights which include species like fedra the plant that produces the decongestant ephedrine and need them an important part of Indonesian cuisine so now let's visit the next branch on the plant

family tree the angiosperms they appeared about 85 million years after the gymnosperms 275 million years ago angiosperm means vessel seed because their seeds are enclosed in a special container or vessel the container is a plant ovary or reproductive organ and when it ripens it becomes a fruit and the ovary is part of a broader reproductive structure completely unique to angiosperms the flower so to repeat flowers are reproductive structures and fruit are ripe plant ovaries beautiful and tasty flowers and fruits helped the angiosperms reach a level of evolutionary success and ecological dominance that hasn't been repeated

in the history of plants there are around 300 000 species of angiosperms today compared to just a thousand gymnosperm species that's a ratio of 300 to one and unless you're in the Arctic Circle nearly every plant in your local environment is an angiosperm Oaks cacti grasses orchids almost every plant you eat is an angiosperm too like kale rice apples carrots and soybeans but the amazing array of flowering and fruiting plants we have today wouldn't have been possible without those early gymnosperm seeds until recently we didn't really know when the angiosperms came about but that all

changed thanks to a prehistoric forest fire a modern day microscope and some brilliant botanists let's head to the thought bubble until the 1980s scientists hadn't found a ton of flower fossils that could tell them about early angiosperms and the ones they had found weren't great since flower words are so soft late tend to go Splat when they become fossils so we lose a lot of valuable information about their structure enter Dr Elsa Marie fries a Danish paleobotanist priests and a colleague were exploring a quarry in Sweden when they discovered that little bits of charcoal in

the Rock contained countless tiny flower fossils they determined that a forest fire swept through the site around 85 million years before turning the flowers to Charcoal this was great news for the botanists because the charcoal hardened the soft features of the flowers preserving them in Exquisite three-dimensional detail so they developed a method for carefully extracting and cleaning the two millimeter flower fossils and use the microscopes to visualize all the tiny details of their structures what they saw was astounding I diverse and complex flowers that were 85 million years old yet recognizable as belonging to the

modern day group that includes witch Hazels and peonies their findings revealed this group of flowering plants was thriving way earlier than previously thought and Dr fries continues her work on charcoal flowers discovering older and older fossils that can help us understand more about the meteoric rise of the angiosperms thanks thought bubble so flowers whether from millions of years ago or today all have structures that enable them to flourish on land a typical flower consists of four types of organs that are arranged in concentric circles in the outermost Circle are the sepals which typically resemble leaves

and protect the flower bud when it's closed next come the petals beautiful showy organs that attract animal pollinators after the petals come the stamens the reproductive organs that produce pollen and the innermost Circle contains the pistol with the ovary and ovules at its base this combination of organs allowed the angiosperms to evolve specialized flower shapes to attract and reward pollinators having an army of insects bats and birds accurately shuttling pollen between your flowers is a way more efficient reproduction strategy than hoping your pollen lands in the right place when it blows by on the Wind

it's like putting the right address on an envelope not just the ZIP code so angiosperms evolved The Staggering diversity of flower shapes and sizes we see today to maximize this pollination potential and similarly fruits evolve to have sense that attract particular animals to eat them those animals then move to another location where hopefully the new plant won't be in competition with the old one and they poop out the seeds inside that fruit it's not pretty but it's effective over about 50 million years the rise of angiosperms triggered what scientists consider an explosive increase in the

number of different land dwelling species both plant and animal this is largely because interactions between angiosperms pollinators and herbivores drove a process called co-evolution where each group influence the other's development and diversification but it was isn't only their appealing flowers and fruits that made angiosperms so successful they also developed ways to harness photosynthesis more efficiently and outgrow other plants their leaves gradually evolved to have more veins that transport water throughout the plant so when there's stomata or pores on their leaves open to absorb carbon dioxide in the air they didn't lose as much water and

could keep growing steadily on top of that angiosperms refined a process of reproduction called double fertilization which essentially allows one sperm cell to fertilize an egg and make an embryo while a second sperm cell creates tissue called endosperm that can provide nutrients to that embryo this made the seeds more likely to grow into successful plants and corn wheat and rice by the way are so nutritious to us because they're basically all endosperm at the end of the day while angiosperms may be the most abundant plant type on Earth plants like bryophytes seedless vascular plants and

gymnosperms still exist and Thrive that's because one plant type isn't better or more evolved than another they're all different and have their own ways of surviving in different environments though yes see it's changed everything and flowers and fruits make my life better there's room for all of us on this big green planet and that completes our tour through the major groups of plants next we'll explore the many ways humans and other organisms interact with their Botanical Brethren hey before we go let's Branch out what's the main trigger for giant sequoia trees to release their seeds

it's getting hot in here find the answer in the comments thanks for watching this episode of Crash Course botany which was filmed at the dimir farisa witch studio and made in partnership with PBS digital Studios and nature if you want to help keep crash course free for everyone forever you can join our community on patreon