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From Wikipedia, the free encyclopedia

Archaefructus
Temporal range: Early Cretaceous
Archaefructus liaoningensis.jpg
Archaefructus liaoningensis - a photograph of a facsimile of the fossil
Scientific classification
Kingdom: Plantae
(unranked): Angiosperms
Class: incertae sedis
Family: Archaefructaceae
Sun, Ji, Dilcher, Zheng, Nixon & Wang
Genus: Archaefructus
Sun, Dilcher, Zheng & Zhou
Species

Archaefructus eoflora
Archaefructus liaoningensis
Archaefructus sinensis

Archaefructus is an extinct genus of herbaceous aquatic seed plants with 3 known species. Fossil material assigned to this genus originates from the Yixian Formation in northeastern China, originally dated as late Jurassic but now thought to be approximately 125 million years old, or early Cretaceous in age. Even with its revised age, Archaefructus has been proposed to be one of the earliest known genera of flowering plants.

Because of its age, lack of sepals and petals, and the fact that its reproductive organs ( carpels and stamens ), are produced on an elongate stem rather than condensed into a flower as in modern angiosperms, Archaefructaceae has been proposed as a new basal angiosperm family.[1] An alternative interpretation of the same fossil, however, interprets the elongate stem as an inflorescence rather than a flower, with staminate (male) flowers below and pistillate (female) flower above.[2] The discovery of Archaefructus eoflora[3] supports this interpretation, because a bisexual flower is present in the region between staminate and pistillate organs. If this interpretation is correct, Archaefructus may not be basal within angiosperms, rather it may be close to the Nymphaeales or the basal eudicots.

"Over the years many contenders have appeared for first true flower in the fossil record. Some of these were eventually reclassified as nonflowers, while others were dated more accurately to a later geological time. Right now, the best and most unambiguous contender for the title of first true flower is (125-130 million years old)[4] Archaefructus sinensis, described in 1998 by Ge Sun at Jilin University and David Dilcher of the University of Florida. Archaefructus was found in Yixian lake-bed deposits in Liaoning Province of northeast China. Dating from the lower Cretaceous age, its scientific name means 'ancient fruit from China.' In an evolutionary rather than a poetic sense, perhaps we should consider Archaefructus as the mother, the Eve, of all living flowering plants."[5]

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  • The First Flowers
  • Angiosperm evolution

Transcription

Angiosperm is the scientific term for a flowering plant. This means that it produces flowers of some sort, which yield seeds. They come in all shapes and sizes, but they’re all still angiosperms. This is different from gymnosperms, which also produce seeds, but they don’t produce flowers and fruits to enclose those seeds. That’s why the term gymnosperm means “naked seeds.” Examples of this would be conifers, like pine trees, or my beloved coastal redwood. In the plant world, gymnosperms evolved first, creating a landscape populated with conifers, cycads and other non-flowering plants. The evolution of angiosperms, however, was famously referred to by Darwin as an “abominable mystery.” So what makes an angiosperm? First, the ovule, the space where an egg is fertilized and grows into a seed, is enclosed and hollow. They also undergo a process called double fertilization. Basically, every pollen grain contains two sperm cells. When these reach a stigma, the “female” anatomy of the plant, one sperm cell combines with an egg cell to form a zygote, which will become a seed. The other “extra” sperm cell combines with a second cell in the ovule, which has a very different purpose. It grows into something called the endosperm, which provides nutrients to that growing seed. The endosperm is basically the energy storage that allows germination to happen. These are only a few of the traits of angiosperms, but outlining them all would require a whole other video. So now let’s talk about how angiosperms evolved! Despite the common characteristics I mentioned, angiosperms are amazingly diverse. They grow all over the world, on land and in the water. Some even grow on other plants; they’re referred to as epiphytes. Air plants, which I’ve talked about in previous videos, are epiphytes! So there are literally hundreds of thousands of angiosperm species around the world. But where did flowering plants get their start? To figure that out, we turn to fossils. The first evidence we have of angiosperms in the fossil record is from 115-125 million years ago. It is in the genus Archaefructus, and based on its morphology, scientists believe it was an aquatic plant. This ties into another of the mysteries regarding angiosperm evolution; there is no consensus on whether angiosperms evolved first aquatically or terrestrially, aka in the water or on land. The earliest fossils we have, like the Archaefructus I just mentioned, were aquatic plants. However, just because that’s the earliest fossil we have, that doesn’t mean there aren’t more, older angiosperm fossils out there. The fossil record is a great resource, but gives us an incomplete picture of the evolution of angiosperms. Regardless, we know that aquatic plants are very, very old, especially the order Nymphaeales, which contains water lilies. A terrestrial group of plants that is very important in angiosperm evolution is the genus Amborella, these are shrubby plants and trees native to New Caledonia, a collection of islands west of Australia. They have evergreen leaves, and flowers that grows from the axils of the leaves. And, it’s vascular system shows some ancient characteristics. Unlike many plants, which have vessels in their xylem, the channel that moves water from the plant’s roots to its leaves, it has tracheids, long cells adapted to moving water. This genus is thought to have branched off early, followed by Nymphaeales, according the a paper from 2007. However, taxonomy and evolution are constantly being re-evaluated and shuffled around, as we get new data from fossils, genetics and other sources. Still, we know that there were many basal branches, resulting in the diverse and widespread angiosperms we know today. What is also unique about the spread and diversification of angiosperms is how quickly it happened. The group of angiosperms known as Mesangiospermae, split into its five major clades inside of about 5 million years, a tiny span in evolutionary terms. And that split yielded 97% of the angiosperms that exist today. I only touched on a couple of the many plants that are significant to our understanding of the evolution of flowering plants. If you’d like to learn more, I encourage you to check out the sources in the description. The big take-away here is that flowers are very, very old, and very, very diverse. Bye Peg! I hope you enjoyed this quick primer on the evolution of flowering plants. There's definitely a lot more to discuss here, so I encourage you to chat about it in the comments, throw any questions you have at me, also if there is an ancient plant that you really love, please tell me about it, or if there is a modern day that has really ancient roots definitely tell me about that too. As always, if you'd like to support Brilliant Botany and help me make more videos like these, you can head over to Patreon and become a monthly supporter, or you can check out the link to merch, buy something there, I've got stickers, hats, t-shirts, all sorts of awesome stuff. Thank you so much to my existing patreon supporters and folks that have bought merch in the past couple of months. I'll see you next week with a new tutorial. See you next time.

See also

Montsechia vidalii

References

  1. ^ Sun, G., Q. Ji, D.L. Dilcher, S. Zheng, K.C. Nixon & X. Wang 2002. Archaefructaceae, a New Basal Angiosperm Family. Science 296(5569): 899–904.
  2. ^ Friis, E.M., J.A. Doyle, P.K. Endress & Q. Leng 2003. Archaefructus – Angiosperm precursor or specialized early angiosperm? Trends in Plant Sciences 8: 369–373.
  3. ^ Ji, Q., H. Li, L.M. Bowe, Y. Liu & D.W. Taylor 2004. "Early Cretaceous Archaefructus eoflora sp. nov. with Bisexual Flowers from Beipiao, Western Liaoning, China." (PDF).  (3.11 MiB) Acta Geologica Sinica 78(4): 883–896.
  4. ^ "Paleobotanists identify what could be the mythical 'first flower'", Proceedings of the National Academy of Sciences, August 17, 2015
  5. ^ Stephen Buchmann. The Reason for Flowers: Their History, Culture, Biology, and How They Change Our Lives. Scribner, NY, 2015

External links

This page was last edited on 13 September 2017, at 04:08.
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