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Mesangiospermae

From Wikipedia, the free encyclopedia

Mesangiospermae
Primula aka.jpg
Primula hortensis
Scientific classification
Kingdom: Plantae
Subkingdom: Embryophyta
(unranked): Spermatophyta
(unranked): Angiosperms
(unranked): Mesangiospermae
Groups
Synonyms
  • Core angiosperms
 Flower of Liriodendron tulipifera, a Mesangiosperm
Flower of Liriodendron tulipifera, a Mesangiosperm

Mesangiospermae (core angiosperms) is a group of flowering plants (angiosperms), informally called "mesangiosperms". They are one of two main clades of angiosperms. It is a name created under the rules of the PhyloCode system of phylogenetic nomenclature.[1] There are about 350,000 species of mesangiosperms.[2] The mesangiosperms contain about 99.95% of the flowering plants, assuming that there are about 175 species not in this group[3] and about 350,000 that are.[2] While such a clade with a similar circumscription exists in the APG III system, it was not given a name.[4]

YouTube Encyclopedic

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  • The First Flowers

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.

Contents

Phylogeny

Besides the mesangiosperms, the other groups of flowering plants are Amborellales, Nymphaeales, and Austrobaileyales. These constitute a paraphyletic grade called basal angiosperms. The order names, ending in -ales are used here without reference to taxonomic rank because these groups contain only one order.[clarification needed]

Mesangiospermae includes the following clades:


Cladogram: The phylogenetic position of the monocots within the angiosperms, as of APG IV (2016)[5]
angiosperms

 Amborellales 




 Nymphaeales 




 Austrobaileyales 






 magnoliids 



 Chloranthales 





 monocots 




 Ceratophyllales 



 eudicots 









basal angiosperms
core angiosperms

Name

The mesangiosperms are usually recognized in classification systems that do not assign groups to taxonomic rank. The name Mesangiospermae is a branch-modified node-based name in phylogenetic nomenclature. It is defined as the most inclusive crown clade containing Platanus occidentalis, but not Amborella trichopoda, Nymphaea odorata, or Austrobaileya scandens.[6] It is sometimes written as /Mesangiospermae even though this is not required by the PhyloCode. The "clademark" slash indicates that the term is intended as phylogenetically defined.[1]

Description

In molecular phylogenetic studies, the mesangiosperms are always strongly supported as a monophyletic group.[7] There is no distinguishing characteristic which is found in all mature mesangiosperms but which is not found in any of the basal angiosperms. Nevertheless, the mesangiosperms are recognizable in the earliest stage of embryonic development.[3][8] The ovule contains a megagametophyte, also known as an embryo sac, that is bipolar in structure and contains 8 cell nuclei. The antipodal cells are persistent, and the endosperm is triploid.

History

The oldest known fossils of flowering plants are fossil mesangiosperms from the Hauterivian stage of the Cretaceous period.[9]

Molecular clock comparisons of DNA sequences indicate that the mesangiosperms originated between 140 and 150 Mya (million years ago) near the beginning of the Cretaceous period.[10] This was about 25 Ma (million years) after the origin of the angiosperms in the mid-Jurassic.[11]

By 135Mya, the mesangiosperms had radiated into 5 groups: Chloranthales, Magnoliids, Monocots, Ceratophyllales, and Eudicots.[11] The radiation into 5 groups probably occurred in about 4 million years.

Because the interval of this radiation (about 4 million years) is short in proportion to its age (about 145 million years), it had long appeared that the 5 groups of mesangiosperms had arisen simultaneously. The mesangiosperms were shown as an unresolved pentatomy in phylogenetic trees. In 2007, two studies attempted to resolve the phylogenetic relationships among these 5 groups by comparing large portions of their chloroplast genomes.[11][12] These studies agreed on the most likely phylogeny for the mesangiosperms. In this phylogeny, the monocots are sister to the clade [Ceratophyllales + eudicots]. However, this result is not strongly supported. The approximately unbiased topology test showed that some of the other possible positions of the monocots had more than 5% probability of being correct. The major weakness of these 2 studies was the small number of species whose DNA was being used in the phylogenetic analysis, 45 in one study and 64 in the other.[11] This was unavoidable, because complete chloroplast genome sequences are known for only a few plants.

References

  1. ^ a b Philip D. Cantino, James A. Doyle, Sean W. Graham, Walter S. Judd, Richard G. Olmstead, Douglas E. Soltis, Pamela S. Soltis, and Michael J. Donoghue (2007). "Towards a phylogenetic nomenclature of Tracheophyta". Taxon. 56 (3): 822–846. doi:10.2307/25065865. 
  2. ^ a b Alan J. Paton, Neil Brummitt, Rafaël Govaerts, Kehan Harman, Sally Hinchcliffe, Bob Allkin, & Eimear Nic Lughadha (2008). "Towards Target 1 of the Global Strategy for Plant Conservation: a working list of all known plant species - progress and prospects". Taxon 57(2):602-611.
  3. ^ a b Peter F. Stevens (2001 onwards). Angiosperm Phylogeny Website In: Missouri Botanical Garden Website. (see External links below).
  4. ^ Angiosperm Phylogeny Group (2009), "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG III", Botanical Journal of the Linnean Society, 161 (2): 105–121, doi:10.1111/j.1095-8339.2009.00996.x, retrieved 2010-12-10 
  5. ^ APG IV 2016.
  6. ^ Philip D. Cantino, James A. Doyle, Sean W. Graham, Walter S. Judd, Richard G. Olmstead, Douglas E. Soltis, Pamela S. Soltis, and Michael J. Donoghue. 2007. Electronic Supplement: pages E1-E44. To: Cantino et alii. 2007. "Towards a phylogenetic nomenclature of Tracheophyta". Taxon 56(3):822-846. (see External links below).
  7. ^ Douglas E. Soltis, Pamela S. Soltis, Peter K. Endress, and Mark W. Chase (2005). Phylogeny and Evolution of the Angiosperms. Sinauer: Sunderland, MA
  8. ^ William E. Friedman and Kirsten C. Ryerson (2009). "Reconstructing the ancestral female gametophyte of angiosperms: Insights from Amborella and other ancient lineages of flowering plants". American Journal of Botany 96(1):129-143. doi:10.3732/ajb.0800311
  9. ^ Else Marie Friis, K. Raunsgaard Pedersen, and Peter R. Crane (2006). "Cretaceous angiosperm flowers: Innovation and evolution in plant reproduction". Palaeogeography, Palaeoclimatology, Palaeoecology232(2-4):251-293. doi:10.1016/j.palaeo.2005.07.006
  10. ^ T. Jonathan Davies, Timothy G. Barraclough, Mark W. Chase, Pamela S. Soltis, Douglas E. Soltis, and Vincent Savolainen (2004). "Darwin's abominable mystery: Insights from a supertree of the angiosperms". Proceedings of the National Academy of Sciences 101(7):1904-1909.
  11. ^ a b c d Michael J. Moore, Charles D. Bell, Pamela S. Soltis, and Douglas E. Soltis (2007). "Using plastid genome-scale data to resolve enigmatic relationships among basal angiosperms". Proceedings of the National Academy of Sciences 104(49):19363-19368. doi:10.1073/pnas.0708072104
  12. ^ Robert K. Jansen, Zhengqiu Cai, Linda A. Raubeson, Henry Daniell, Claude W. dePamphilis, James Leebens-Mack, Kai F. Müller, Mary Guisinger-Bellian, Rosemarie C. Haberle, Anne K. Hansen, Timothy W. Chumley, Seung-Bum Lee, Rhiannon Peery, Joel R. McNeal, Jennifer V. Kuehl, and Jeffrey L. Boore (2007). "Analysis of 81 genes from 64 plastid genomes resolves relationships in angiosperms and identifies genome-scale evolutionary patterns" Proceedings of the National Academy of Sciences 104(49):19369-19374 doi:10.1073/pnas.0709121104

Bibliography

External links

This page was last edited on 24 December 2017, at 17:35.
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