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Angiosperm Evolution & Flower Diversity
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0:01
[Music]
0:22
the next time you're admiring a plant consider that you and every other animal are meant to admire a flower's color shape and smell flowering plants may have arrived late in the Earth's history but they evolved fast and they displaced many other kinds of plants we often think of flowers as very delicate plants and that's not exactly wrong but they are also worldclass competitors who took over the planet what is the secret of flower power Charles Darwin was also confounded
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by this question in 1879 Darwin read an essay by another scientist John Ball and that essay was titled on the origin of the Flora of the European Alps the essay was given at a meeting of the royal geographical Society in June of 1879 in Ball's essay he notes that the fossil evidence of flowers appears very rapidly he then goes on to wonder how the flowers appeared so rapidly and diversely if evolution by natural selection were really responsible for their appearance
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in other words according to Bell and the fossil record flowers appeared in the lake Cretaceous about 145 million years ago and then there were so many different types seemingly all of a sudden John Ball questioned how natural selection could account for flowers sudden appearance where did their ancestors come from and how could natural selection operating on a long time scale by Darwin's definition provides so many different kinds of flowers so quickly so later that same year 1879
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Darwin wrote a letter to his friend and fellow scientist Joseph Hooker in it Darwin writes the following sentence the rapid development as far as we can judge of all the higher plants within recent geological times is an abominable mystery the phrase abominable mystery becomes one of the most of qued Darwin phrases of all time and probably one of the most popular quotes about flower evolution in general what Darwin meant was that ball really had him on this one
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he didn't know how natural selection could explain the rapid evolution of flowering plants it went against one of Darwin's Central posits about Evolution via selection he said n Nonet salum or nature never makes leaps consider this the first flower from the fossil record appeared 125 million years ago this was archaus which means old flower this plant is extinct now but there it appeared in the fossil record the flower may be IND discernible because it's small and inconspicuous but
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it is present and that's what makes this plant unique it's a short shrubby plant with small flowers but the flowers are there then a mere 40 million years later there's flowers everywhere this is a relatively short evolutionary time consider that the first land plants arose about 420 million years ago in the saluan and it took another 293 million years to get to the first flower and then 40 million years later there are flowers everywhere even more puzzling flowering plants are the
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dominant form of planet of plants on the planet depending how you count they're anywhere from 330,000 to 400,000 species of flowering plants you can see why this would be a dilemma also at the time there was nothing that looked even remotely like an intermediate there were cones from the conifers and there were flowers cones don't look too much like flowers so how did flowers arise in 1879 though the fossil record wasn't nearly as clear as it is now we have a much better
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understanding where flowers came from and how that Evolution could have happened much quicker than Darwin suspected we now know about more mechanisms for the creation of new species than were known during Darwin's time for example we Now understand polyploidy which is where the chromosomes can double or triple during reproduction and we also have a much better picture of the fossil record in fact in a paper from 2013 Peter a Huli and Suzanne Fe Burkhart found pollen from an extent flowering
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plant called afropollis in Northern Switzerland that they estimate to be between 252 and 247 million years ago or even earlier that would be 100 million years earlier than the date Darwin found so abominable they also suggest that the pollen is of a type that is usually insect pollinated most likely from beetles given that beetles were also present during this time such a plant could have been like present day gymnosperms that extra 100 million years certainly helps Darwin out a bit still
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pollen isn't a flower it could be that flowers just don't fossilize very well which they don't some botanists have suggested we're just not looking in the right place it may also be that early flowers were just small the conifers and sads of the Jurassic were so dominant that flowers were just waiting in the understory so to speak this scenario was true of early mammals which were also small but got bigger after the demise of the dinosaurs Additionally the flowers may
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not have been Woody and again this would have limited their ability to form fossils interestingly molecular evidence puts the Advent of the flowering plants back to about 290 million years ago way before the Cretaceous How would ular evidence even work in trying to determine the age when something from that long ago evolved the main molecular technique used is that of the molecular clock this basically looks at DNA within an organism that would change on a regular
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basis that is an organism that has a background rate of mutation that wouldn't be associated with reproduction or natural selection generally with plants botanists are looking at similar ities or differences within a particular piece of chloroplast DNA this technique assumes that the DNA within the chloroplast changes at a regular rate and that the more different it is from current DNA the longer ago it must have come on the scene why the fossil record and the molecular evidence don't match up
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probably has to do with those ideas we mentioned about early flowering plants not being the best at forming fossil whatever the exact origin of the flowers we do have some good evidence of what very early flowers may have looked like and how they might have evolved from conifers bists also tend to agree that the flowers form a good group also called a monoptic group that is a group with one descendant and all of The Offspring yet other bists suggest that the flower may have evolved more than
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once still Conifer and fern and mosses have been around much longer than flowering plants so how were there so many different species of flowering plants in such a short time the answer May lie in the fact that many flowering plants are both pollinated and dispersed by animals an animal moving pollen between plants could become more specialized and get pollen from only one type of plant now the plants pollinated by that animal are reproductively isolated from other plants this is the
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key to speciation or the formation of new species the other way animals can be key in speciation is through dispersal if an animal disperses a seed to a new environment it can be in a new island figuratively speaking that is the animal has dispersed the seed to a new location where it can no longer breed with its old population so it becomes reproductively isolated and speciation occurs now would be a good time to remind ourselves about the taxonomy that Bist used to describe groupings of
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plants do you remember our pneumonic device King Phillip Came Over from good Spain King stands for Kingdom the easiest we're only doing one Kingdom in the whole course and that's plants Philip stands for Fila we've discussed a few Fila we started with mosses the brop we talked about ferns to R and then we learned all about pinoid the largest film of the conifers class is the next grouping of different orders there are essentially two classes of flowering plants the next level down the
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order is helpful in thinking about evolutionary relations of plants like class it's named for the type family that best represents the order there are dozens of orders and so one example is the Lamey Ales all orders end in the suffix Al's so there's a sort of rule for you in botney it's named after the family lame which is the mint family but it also includes about 20 other families like the verban which include the verbina herbs and the oi AC or the olive family the family level in botney such
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as the Lamey AC that we just met always ends in the suffix a AE the largest plant families in terms of numbers of species are the orchida the orchids the asers which are the sunflowers and the fabas e or the peas and then the last two groupings are genus and species A genus is a particular grouping within the plant family and the species name is actually comprised of both the genus and the specific epithet in a sense this is like having a last name and a first name only
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what we think of as a last name comes first and this is akin to the Chinese way of naming so for example when we discussed pinus Ponderosa the pinest part is the pine genus and the specific epithet Ponderosa describes which Pine we're talking about the ponderous or heavy one together the genus and the specific epithet make up the scientific name and we call this a Latin binomial because it's Latin and a scientific name it should always be written in a certain
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way with the genus capitalized in the specific epithet lower case and the whole thing should be italicized or underlined in fact this is the way we would write our own scientific name Homo sapiens the binomial system of biological nomenclature was developed by Swedish botanist Carl lenus but it's also used for animals protus and fungus too bacteria and viruses are harder to classify to the species level because it's difficult to know where one species stops and another species begins but
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generally field botanist those interested in identifying plants in the field focus on the family level and families are named after the type genus within that family which is the genus that typifies the traits of the family for example the genus pinus is the type genus for which the family is named another example would be the sunflower family the type genus of sun flowers is aster so the family name is aster there are about 600 families of plants and some of that number depends
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on the different ways molecular evidence might be used to define some of the families some bsts might lump two families together where another will split them the grouping of living things like this is called taxonomy Carl anaus lived in the 1700s so he predated Darwin now lenaeus was a Swedish doctor and at this time in the mid 1700s all doctors were gardeners and botanists since most medicines were derived from plants or fungus lenus organized living things
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into a system that is still the basis of the system we use today all of his Arrangements of plants were based on reproductive structures using evolutionary relations within such groupings is called systematics so so there's a slight difference between these two taxonomy simply says knife Fork spoon Spork Chopsticks systematic says which came first knife as the simplest and as a necessity to hunt then Fork Chopsticks clearly didn't evolve from Fork so that must be a separate
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group I hope you can appreciate the difference botanists don't really do simple taxonomy without evolutionary relations but knowing a few Ames even if you can't remember the evolutionary difference between them helps a lot when trying to identify plants in the field as each new scientific Advance came along the sequence of these groupings were changed a bit but none changed the thinking nearly as much as molecular evidence as with many things in botney molecular evidence has changed
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the way we once thought about the evolutionary progression of flowering plants now as I mentioned bnst focus on the family it used to be thought that the earliest flowering plants were those like in the Magnolia family big showy flowers and you can almost imagine the center part of the flower looking a bit like a cone and but the next came a hypothesis that the earliest fossil flowers were quite small and looked more like those in the piper family or the piper AC once again molecular evidence
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provides a bit of an alternative in 2013 the entire Genome of a small weedy shrub native to New calonia had been sequenced interestingly Darwin actually suspected that the center of flowering plant Evolution had been a distant place that science had not yet discovered and new calonia is an island in the South Pacific for the decade before this full genome sequence was completed botanists had used a variety of molecular techniques to determine that this shrub amberella Tropa was the oldest extent
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flowering plant this shrub is the only member of the amberella AC and probably had other relatives that were alive sometime in the past it turns out that this shrub is the sister group to all of the flowering plants indicating that indeed it is a common ancestor to all flowering plants this shrub gives us some clues about what the earliest flowering plants might have looked like because it's a shrub botanist can confirm the hypothesis that the earliest flowering
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plants were Woody however due to its weedy growth in the underst story likely the first flowering plants were not towering trees like many of the gymnosperms this plant is dous which is another clue about the early flowering plants how might a flower even a rudimentary flower have developed there are several models for how this might have occurred the best genetic techniques indicate that the same genes that are responsible for flower development in amberella are the same
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genes that are responsible for the formation of the male cones of the gymnosperms so it seems the flower developed from the male cone before we talk about the diversity of flowering plants and there are anywhere between 300,000 and 400,000 of them depending on how you count we should assure ourselves that we understand all the different parts of a flower there are very few rules in botney but here's one I challenge you to check for yourself all the flowering
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plants have an outer ring of male parts with an inner ring of female parts in botney when something forms a ring we call it a WHL so the male parts of the flower WHL around the female parts in all flowers that is the case for all flowers supports the eye aide that the flower only arose once in evolutionary history okay so what are those male and female parts of the flower male parts are called stamans and that's pretty easy to remember because they are men Stam men have an anther
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with a pollen and a stalk called the filament the female part our parts are a bit more complicated there is a top part called the stigma I like to say the sticky stigma stigma because this is where the pollen will land the stigma then becomes the style I like to say the Stylin style because it's usually long and thin and connects to the ovary at the base the ovary is where the ovule is housed and collectively the female part is called the carpal or the pistol at a minimum flowers have either
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male or female parts the typical flower has both male and female parts and they're called perfect flowers but some flowers can be all male called staminate flowers and others can be all female called pistolet or carpet flowers the petals and seil are the perianth and this part is optional some flowers have them and other flowers don't but flowers such as black pepper Piper nigram do not have the peran and flowers don't have to have seil which are the typically green
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leaves under the petals sometimes the petals and Steeples can't be distinguished so they're called tles the flowers of magnolia trees have tles for example the arrangement and the number of stamans and carpal petals and seil varies with various families and this was the distinguishing factor that lus used to categorize his families of plants Lana has famously described stavens and carpal in terms of Bride and grooms so in describing a flower that had five stamans and one carpel he would
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describe it as one bride in a bed chamber with five groomsmen he did so to appear modest but there was quite a bit of outrage about this seemingly perverse nature flowering plants are called the anopa or the angiosperms which means closed vessel recall that gymnosperm meant naked seed and so angiosperm comes from the Greek angion vessel and refers to the seed so instead of the cones which have open seeds these plants will enclose the seed in an ovary that then swells to become the
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fruits the film of flowering plants the anthoid is traditionally divided into two classes going back to a taxonomy published in the 17th century by botanist John Ray which he called dcot and monocots however the term dcot isn't used anymore because it doesn't represent a true evolutionary group instead of dcot Bist used the term uots so why weren't these good groups but first let's look at the difference between these two classes which are still used just with UDOT instead of
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dcot and then look at why the name dcot had to be changed a bit as you were probably taught at some point the term dcot refers to dialon the Calon is the seed leaf or the first leaf that emerges in the developing plant in diots there are two calans that emerge at the same time in monocots there's only one seed Leaf the difference between these two groups of plants can also be seen in several different physical aspects of the flowers the veins and the leaf and
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the arrangement of the vascular tissue in cross-section so let's begin with the flowers monocots have flower s in groups of Threes that means monocot can have three six or even nine stamans and three or six carpal monocots will also have three petals and three seil like Trillium or six petals and six seil like most lilies diecuts have flower parts in fours or fives notice how the seil petals stamans and carpal are all in multiples of fours or five what's funny
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about using Botanical Keys is that you usually after eight or 10 the number just becomes many or even infinity and I like to joke that bists don't really like to count past 10 let's look at leaf ination and this is just what it sounds like the veins running through the leaf of xylm and flum in monocots the leaf veins are parallel like the veins in a grass blade because a grass is a monocot in diecuts the leaf veins are netted like a feather or like a palm pretty pretty much anything but
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parallel the dicots have a tissue Arrangement that is reminiscent of that which we saw in Woody plants in fact most trees are uots or belong to one of the groups that was removed from the dcot all together these removed groups are called the basil angiosperms the uot vascular tissue Arrangement has rings around the outside of the stem with flum on the outside and dyum on the inside just like the Woody stem only now there is no Cork cambium and no bark so the dcot can have
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secondary growth which is outward growth and wood development but they don't have to do this the monocots don't have secondary growth at all so the monocots don't have True Wood the monocots have vascular tissue arranged in what I fondly learned as monkey faces essentially these bundles are arranged throughout the plant and they consist of two large column of xylem which look like eyes and flam cells which look like a forehead this vascular bundle also has a small space called the Lune which
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looks a little like a mouth I don't know maybe it's not a great analogy but if you squint you can just make it out so why the new word uots these seem like nice divisions but there are a number of flowering plant families that don't fit very nicely in either of these two categories for example the water lily family Nim face e have a stem Arrangement that looks like a monot they have six seil and they have what looks to be one Calen but they have netted Leaf venation the question then becomes
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where to put this family as it turns out there are a few maybe a dozen or so families in this predicament and so many botanists lump them together in a group called The basil angiosperms the term basil implies that they're at the base of the pH genetic tree of the flowering plants this is not a very large group as they make up less than 5% of all of the flowering plants basil angiosperms often show combinations of the following traits numerous flattened or lamin or stamans
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with wide filaments numerous tles which are indistinguishable petals and seil many separate carpal and Alternate spirally arranged leaves that's the old dcot name used to include many of the basil angiosperms once these plants were taken out of the diecuts the new name the new name became uots or true diots I mean who knows what those basil angiosperms are indeed they're not a cohesive group but they fit better on their own than they do in the monocots or the old
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diecuts one plant family in this group that students usually remember as a basil angiosperms is the Magnolia family the Magnolia AC the ending AE implies a family the Magnolias have always been placed at the bottom of the flowering plants probably because the carpal in this group superficially resemble cones while they're not cones this group is still in the basil angiosperms mainly due to the numerous teil and many separate carpal which can be seen in the cone-like structure of the carpal each
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one of those divisions is a carpal that houses an U and that is where the bright red seeds of the Magnolia are born so thinking about the evolutionary tree of the flowering plants it might go something like this our oldest fossil flower is archa fructus it was a simple shrubby plant but clearly a flower fast forward about 127 million years and we have the species amberella Tri capota this is the living sister group to all the remaining flowering plants from here
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the basil angiosperms were likely next on the scene and from a common ancestor to the basil angiosperms the monocots and ticot appeared in terms of diversity as we mentioned only about 5% of flowering plants are basil angiosperms the monocots comprise about 25% and all the rest are uots as I mentioned there are probably between 300,000 and 400 100,000 species of flowering plants but botas don't seem to have as many words to describe the shapes of flowers as the shapes of
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leaves when I think of flower shapes I generally think of symmetry flowers can be radially symmetrical or bilaterally symmetrical there are a few descriptors like tube-shaped and bell-shaped flowers but other terms would be reserved for specific flowers and Bist don't use them broadly I think this is because there are so many other ways to just determine the family to which a plant belongs by looking at the flower most Wildflower ID books will use color others will use
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infloresence types an infloresence describes how the flowers are arranged on the stem there are quite a few descriptors of inflorescences a single flower on a stem is called the solitary inflorescence and flowers that alternate up the stem is called an inflorescence that called a reim if those flowers are tightly compressed on the tip of the stem it's called a spike an inflorescence that has numerous flowers forming a sort of umbrella shape is called an Umble from the Latin umbella
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meaning sunshade which also gives us the word umbrella but the most deciding factor in the determination of the species is the number and arrangement of the male and female parts for example members of the the Hibiscus family the malvasi have the stamman forming a tube around the pistol or coming off directly from the pistol this is called a monod delus staman and it's a key giveaway for this family of course most children are taught that flowers are showy and smell
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nice to attract pollinator animals that will enable the plant to exchange pollen however there are other adaptations of flowers that are not reproductive a 2006 review chapter in the book ecology and evolution of flowers Sharon Strauss and Justin Whittle review a number of published studies that show a correlation between pink and purple flowers and drought or heat stress remember that flowers of the same species can have different colored flowers the same as humans can have
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different hair colors anthocyanins are pigments not only in the leaves but also in the flowers where they cause flowers to be any huge of red or pink anthos are also the most common pigments in flowering plants perhaps because red and pink are also associated with stress so in the Strauss and Whittle review the plant that had pink or purple flowers had greater levels of anthocyanins these antho iins were also in the leaf where they helped the plant cope with higher levels of heat or
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drought so here is an example where flower color isn't related necessarily to a pollinator preference but to a physiologic response additionally pollinators may prefer large flowers but large flowers are energetically and hydrologically expensive from the point of view of the plant there's a trade-off between attracting pollinators and making flowers small enough that there's enough energy to make a fruit for later dispersal of the seed and that keeps the flower size modest in most plants
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the world's largest single flower is the Veria Arnold ey from the rainforest of Indonesia what do you think ticot or monocot it has five Paragon lobes which are essentially giant hardened petals it's a UDOT the largest record of the individual flower was measured at over 1 meter across that's about 3et 4 in this single flower weighed 24 lbs how about that for a corsage it's a parasitic plant with no visible leaves roots or stem which may be why it's able to shunt all of its
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energy into its massive flower size interesting the common name is corpse flower because it smells like Rotting Flesh and this is also the common name of the plant with the largest inflorescence remember that the infloresence is a collection of individual flowers on the stem now the largest in fluorescence goes to another corpse flower but this one is called called amorpho thalis titanum or the Titan arum this is the corpse flower that Botanic Gardens will often put on
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special display when it flowers because it doesn't flower very often this inflorescence can grow to a height of 3 m or 10 ft the leaf of this plant can grow 6 M or 20 ft tall It generally takes about 7 to 10 years for the first flower to bloom and then it may bloom more frequently like every 2 or 3 years or it might not no rules in botney but there are patterns why might both of these super sized flowers smell like Carion the answer is to attract flies the Titan arum is a monocot and
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the Ria is a UDOT but they both live in Sumatra so something about Sumatran rainforest has pollinators that are attracted to the smell of Rotting Flesh these pollinators turn out to be carrying eating beetles and flesh flies both of these animals seek out rotting meat and these corpse flowers trick them into thinking they found it but not before the animals have done the plants bidding and moved pollen from one plant to another certainly these beetles and flies must think corpse flowers an
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abominable mystery so the next time you are admiring a flower its color its smell or its shape remember that you and every other animal are meant to admire it you're doing exactly what the plant wants
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