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Plant evolution has played a critical role in shaping the world we know today. Since first appearing millions of years ago, plants have molded the earth to suit their needs. From changing the balance of gasses in our atmosphere, to physically altering earth's landscapes. There is no doubt that our planet would be fundamentally different without the emergence and evolution of the plant kingdom.
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Jetzt kostenlos anmeldenPlant evolution has played a critical role in shaping the world we know today. Since first appearing millions of years ago, plants have molded the earth to suit their needs. From changing the balance of gasses in our atmosphere, to physically altering earth's landscapes. There is no doubt that our planet would be fundamentally different without the emergence and evolution of the plant kingdom.
Plant evolution refers to how plants originated and all the changes they have gone through since then while dispersing through Earth and adapting to different environments.
Plants have evolved through the same mechanisms affecting all life on Earth. Much like animals, bacteria, and fungi, the different conditions plants faced influenced their evolution.
This process is known as evolution. Natural selection is one of the mechanism by which evolution occurs.
Evolution: a gradual and cumulative change in the heritable genetic traits of a population of organisms over the course of many generations.
Natural selection: a process where individuals with traits that help them survive in their environment are more likely to survive and reproduce because of those traits. These beneficial traits become more and more common within the population with each passing generation.
Tracking these changes in individuals and conditions through time paints a picture to better understand how the diversity of plant life across the terrestrial world came to be. This knowledge can help us to predict responses to climate change, droughts, and other challenges our society will face, and may even influence how we respond to these threats.
It's widely believed that life started underwater. The origin and evolution of plants started roughly 430 million years ago when the ancestor of plants migrated to terrestrial land and gave rise to today's land plants. The ancestral streptophyte algae is thought to have been the only plant ancestor to survive the move onto land4.
The origins of life itself are hotly contested, but it is mostly agreed that all life stems from a single common ancestor.
Modern-day plants have complex stress signaling pathways with many similarities to the ancestral streptophyte algae4. This indicates it was not an easy transition from water to land and strong selection pressures would have been at work.
This symbiotic relationship may have occurred due to food scarcity. In an environment lacking prey, capitalizing on freely available sunshine for energy would be very beneficial. By absorbing rather than consuming photosynthesizing cyanobacteria plant ancestors would have also gained this beneficial trait.3
In the eyes of evolution, you either adapt or face extinction. Initial terrestrial environments were rife with available sunlight, and space to grow whilst lacking predators and competitors. However, the move to land was still a particularly stressful time for early land plants.
Land plants that couldn’t adapt to their new environment were outcompeted for resources, and simply couldn't survive the harsh conditions. The threat of Extinction was constant for early land plants. Some of the deadly threats and consequences of terrestrial life included:
Desiccation - Early land plants couldn’t transport water, so relied heavily on damp conditions.
UV radiation - Water may filter sunlight, and reduce the amount of energy absorbed by chlorophyll pigments, but it also acts as a barrier against harmful UV radiation. A barrier absent on land.
Lack of structural support - Water offers aquatic plants support and buoyancy, but in terrestrial environments, plants must devote energy and nutrients to rigid features like cell walls.
The harsh selection pressures of early terrestrial environments shaped land plant's evolutionary journey. Yet, since their emergence in the late Ordovician Period, land plants have reworked our planet to suit their own needs. Paving the way for some species to blossom, whilst ensuring the extinction of others.
Importance | Description |
The development of roots changed the earth's physical environment | As plants spread across land, previously bare riverbeds became flourishing plant habitats. Plant roots held the earth together and reduced erosion on river banks. This resulted in an increase of meandering rivers, rather than the wide braided channels common before the emergence of land plants.
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Land plants drove early mass extinctions | As plant roots burrowed down into the earth, the rocks beneath were worn down. Releasing minerals that found their way into earth's river systems and oceans. This sudden increase in nutrients caused the eutrophication and anoxia of past oceans, killing half of marine life in the Devonian Mass Extinction. |
Plants and algae changed the earth's atmosphere | Plants and algae are autotrophs. They absorb carbon dioxide and energy from the sun, whilst releasing oxygen. Plants and algae dramatically increased the ratio of oxygen in the atmosphere during the carboniferous period, allowing a boom in animal evolution. With oxygen no longer a limiting factor, huge arthropods emerged. |
Plants influence the global climate | Photosynthesis directly increases atmospheric oxygen concentrations, but plant roots also played a role by breaking up the earth and releasing minerals which react with carbon dioxide. These reactions draw down atmospheric carbon dioxide and lock it away in the earth and oceans. This dramatically increased the concentration of oxygen in the atmosphere, leading to global cooling periods and ice ages. The mass extinctions which occurred during ice ages, opened up niches for surviving species to adapt and colonize. |
Table 1: The main changes that plants caused in Earth’s environment reflect the importance of plant evolution.
The timeline of plant evolution spans, according to the existing evidence, from about 430 million years ago in the late Ordovician Period until modern times. Land plants' ability to flourish is largely attributed to adaptations gained through four key evolutionary steps, which no doubt evolved under harsh selection pressures.
Fig. 1: The origina and evolution of plants. Key steps in plant evolution throughout different geological periods.
Angiosperms, which underwent each key stage of plant evolution, are now the most abundant of all land plant types.
Billions of years of plant evolution have allowed land plants to conquer every corner of the globe. So much so that land plants now make up 82% of global biomass. Let's see some examples of plant evolution that show the different ways they have adapted to land.
Adaptation | Example of the Benefits Bestowed on Plants. |
Waxy cuticle | Prevent water loss, reducing the risk of desiccation. |
Increased gas exchange needed for respiration and photosynthesis. Guard cells control how open or closed the stomata are, reducing water lost by transpiration and desiccation risk. | |
Rhizoids | Provide structure and some uptake of water in bryophytes. |
Vascular system | Transport nutrients, water and energy in the form of ATP from where they are absorbed, or produced, to tissues where they are needed. Vascular plants are able to grow much taller, outcompeting other plants for sunshine, because of their vascular systems. Vascular plants also have increased rigidity and support. |
True roots | Anchor and support plants, and aid in the absorption of water in vascular plants. |
Protective flavonoids and pigments | Protect plants from UV radiation by filtering harmful UV light whilst still allowing for some energy absorption for photosynthesis. |
Nectar & variations in color, scent and size of flowers | Sweet nectar encourages insects and other pollinators to travel deep into the flowers, where sticky pollen attaches to their skin or fur. As pollinators visit multiple flowers in a day, some of this pollen will rub off on future plants, fertilizing and spreading the initial plant's genes. Plants make their flowers more inviting for pollinators through the use of bright colors, appealing scents, and different sized and shaped petals. Angiosperms, or flowering plants, have coevolved with pollinators. |
Seeds and pollen | Allow the genetic material, and eventually fertilized embryos of plants to travel far away from their parents and reduce competition for resources. Seeds and pollen both also have protective coats which protect their contents from mechanical damage and desiccation. Seed plants are able to survive and spread through much harsher environments thanks to this adaptation. |
Fruit surrounding seeds | Angiosperms' seeds are surrounded by fruits or ovaries. Sweet fleshy fruits invite animals to eat them, dispersing the seeds contained within through their feces. This increased dispersal reduces competition from parent plants in angiosperms. Other fruits are dry and hard. These fruits confer additional protection to the seed. Some of which may have hooks that attach to the fur of pollinators aiding dispersal. Not all seed plants benefit from the evolution of protective fruit, as gymnosperms lack ovaries. |
Table 2: The key adaptations that plants developed to adapt to terrestrial conditions.
The evolution of gymnosperm plants can be explained as follows: they were the first seeded plants to evolve from vascular plants during the late Devonian or early carboniferous period. Gymnosperm plants’ novel seed and pollen adaptations to wind allowed them to disperse throughout and survive the dry conditions.
The major events that highlight the evolution of plants are: the move to land, the evolution of the vascular system, seeds, and flowers. These adaptations increased the survival of plants within the dry terrestrial conditions as they conquered the land.
The proposed sequence in plant evolution starts with the move of the ancestral streptophyte algae onto land. Next plants evolved vascular systems, gymnosperm seeds and eventually the angiosperm seeds and flowers which make up 80% of known plant life.
The four major periods of plant evolution are: the move to land during the Ordovician-late Ordovician period, the development of vascular tissue in the Devonian period, gymnosperm emergence in the carboniferous period, and angiosperm emergence in the Cretaceous period.
There are numerous examples of evolution in plants under natural selection. In the late Devonian period vascular plants evolved ‘naked seeds’ as an adaptation to dry conditions.
The timeline for the evolution of plants, based on the major events, spans from their emergence about 430 million years ago in the late Ordovician Period to the rise of flowering plants in the Cretaceous Period.
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SIGNUP SIGNUPFlashcards in Plant Evolution34
Start learningIf life evolved in water, how did land plants migrate to the terrestrial world?
Lands plants migrated to land once. All land plants share a single common ancestor known as ancestral streptophyte algae.
The similarity in the stress signaling pathways between modern plants and ancestral streptophyte algae has been shown to be very high suggesting these pathways were beneficial for adapting to lands many stressors.
When did early ancestral plants make the move to land?
Ancestral streptophyte algae moved to land roughly 430 million years ago.
Once on land why was it important for plants to adapt to their environment?
Modern plants and ancestral streptophyte algae share complex signalling pathways. This suggests it was harsh transition from aquatic to terrestrial environments. In the novel terrestrial environment it was crucial plants evolved desiccation strategies to survive the dry conditions.
Further evolution was critical to reduce competition for resources, resist against UV damage, and disperse into new environments.
Which feature of ancestral streptophyte algae may have been beneficial for surviving early terrestrial environments?
Cell walls containing lignin like compounds
Which of the following could NOT be considered a beneficial adaptation to avoid dessication?
Protective Flavonoids and Pigments
In what period did early angiosperms evolve?
Cretaceous period
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