The world we live in today would look completely different without land plants. They have had a huge impact on Earth's geography and atmosphere. But how did these changes happen? It all started with a few key adaptations made by land plants. By tracing the timeline of plant evolution, we can travel back through time and see how these changes occurred.
To reconstruct this timeline, scientists use something called phylogenetic trees. These trees combine different types of evidence, like fossils and chemicals, to create a picture of how plants evolved over time. Fossils are the most reliable source of information when it comes to creating this timeline. They show us when different plant traits emerged and how they evolved.
From studying the fossil record, we've learned a lot about plant evolution. One of the most significant findings is the increasing speed of evolution and the complexity of plant communities as they adapted to life on land.
There are four key stages in the timeline of plant evolution. These are:
Each of these stages reflects the challenges plants faced as they adapted to new environments. By understanding this timeline, we can better appreciate the incredible journey plants have taken to get to where they are today.
Moving from water to land was not an easy feat for plants, but it did come with some benefits. Since plants made the transition before animals, they didn't have to worry about predators at first. Plus, there was more CO2 and sunlight available for photosynthesis. This helped early land plants grow and spread.
But the transition also came with its own challenges. Water helps filter out harmful UV radiation, which land plants didn't have. Nutrients diffuse slower in water, but it also provides buoyancy and support. Early land plants had to adapt to survive in this new environment. They had to find ways to avoid drying out and to protect themselves from the sun's rays.
These challenges highlight the importance of early land plant evolution. Once they adapted to life on land, they were able to grow and reproduce in new ways. But these changes didn't happen overnight. We can track the evolution of plants over time by studying fossils. By doing so, we can see how early land plants evolved to survive in a harsher environment and eventually became the diverse range of plants we know today.
Plants underwent 4 key steps within their evolutionary history: the move to land, followed by the evolution of vascular tissue, seeds and pollen, and flowering plants. Each of these adaptations emerged in different geological periods and in a sequential order (Fig. 1).
The timeline of plant evolution spans many millions of years. In the chart below (Fig. 1) you can see when each of the sequential steps took place.
When ancestral streptophyte algae made the move to land, it went through several stages of evolution before becoming the diverse range of land plants we see today. The earliest land plants were most closely related to bryophytes, which likely appeared around 450 million years ago during the Ordovician Period.
Unfortunately, the fossil record for early terrestrial plants is not very good since they were made of soft organic material. But by studying bryophytes and liverworts, we can learn more about these early plants. It's believed that they were small and lacked support, so they grew close to the ground in damp environments. They also didn't have a specialized transport system, meaning they couldn't move water around their bodies like modern plants do.
Early terrestrial plants relied on water for sexual reproduction, with male gametes swimming through water to fertilize female gametes. This was their only method of transportation since they didn't have any other means of getting around.
While early land plants faced many challenges, they eventually evolved to become the diverse range of plants we see today. Studying their evolution helps us better understand the history of life on Earth.
The next stage in the evolution of plants was the development of vascular systems. These systems are similar to our veins and arteries and transport water and nutrients to different parts of the plant. Vascular plants likely evolved in the late Ordovician Period due to high competition for sunlight. The development of vascular systems allowed plants to grow taller and access more resources since they were no longer constricted by diffusion and osmosis to transport key nutrients and water.
With the evolution of vascular tissue came the development of true roots. Roots allowed plants to access more water and anchor themselves for stability as they grew taller. Early vascular plants didn't have seeds but relied on water to reproduce sexually, just like non-vascular bryophytes.
Ferns and club mosses are descendants of early vascular plants and are seedless plants that reproduce via spores. These plants are still around today and give us a glimpse into the past and the evolution of plants. Understanding the evolutionary history of plants is important for understanding the diversity of life on Earth and how it has changed over time.
The evolution of seeds was a game-changer for land plants. Seeds eliminated the need for watery environments for reproductive purposes, and they contained nutrients that allowed developing embryos to lay dormant until conditions were favorable for their growth and survival. Seeds also had a protective coating, extending the dispersal range of new plants, reducing their competition for resources with their parents.
Gymnosperms were the first seeded land plants to evolve, producing specialized male and female spores in different cones. Later, during the Cretaceous Period, angiosperms evolved, which produced male and female structures within flowers. The emergence of flowering seed plants seemed to occur all at once, a phenomenon known as the "abominable mystery" due to gaps in the fossil record.
During the Cretaceous Period, angiosperms spread far and wide, replacing and outcompeting the previous fern inhabitants. Most angiosperms have a symbiotic relationship with a pollinator, evolving to have brightly colored flowers of different sizes, shapes, and scents, containing sweet nectar to attract pollinators. Pollinators have also evolved traits to better reach the nectar they feed on. This coevolution between angiosperms and their pollinators is a great example of how species can adapt to each other over time.
The evolution of seeds and pollen allowed land plants to migrate into every terrestrial niche, survive on dry land, and dominate the globe. Gymnosperm land plants dominated the terrestrial landscape from their emergence through the Triassic and Jurassic periods, only to be replaced as the "king" of seed plants 100 million years ago by angiosperms and their flowers during the late Mesozoic Era. Understanding the evolutionary history of plants is crucial to understanding the diversity of life on Earth and how it has changed over time.
Plant Timeline Evolution - Key takeaways Plant evolution can be tracked throughout the fossil record starting with the origins of life ~3.7 million years ago. Land plants were up against a great number of stressors when they first appeared on land. These stressors caused strong selection pressures and shaped the evolution of land plants. There are four key sequential steps throughout plants evolutionary history. Whilst flowering plants make up 90% of today's flora, they possess significant gaps within the fossil record. Little is known about the exact evolutionary journey of flower plants after they branched from gymnosperms in the late Devonian period. Angiosperms and their relevant pollinators are a great example of coevolution.
References Lumen, Bryophytes, Boundless Biology C. Jill Harrison et al, The origin and early evolution of vascular plant shoots and leaves, Philosophical Transactions of the Royal Society B, 2018.T. Jonathan Davies et al, Darwin's abominable mystery: Insights from a supertree of the angiosperms, Proceedings of the National Academy of Sciences of the United States of America, 2004.
What are the four major periods of plant evolution?
The four major periods of plant evolution were the move to land, the development of vascular tissue, and gymnosperm and angiosperm emergence. Occurring within the Ordovician, late Ordovician, Devonian & Carboniferous period and Cretaceous period respectively.
What is the order of the evolution of plants?
The order of evolution in plants is: 1. The move of the ancestral streptophyte algae onto land. 2. Early land plants evolved vascular systems. 3. Seed plants evolved. 4. Flowering plants evolved.
When did plants transition from water to land?
One common ancestor of plants, known as ancestral streptophyte algae, moved to land in the Ordovician period of the Palaeozoic era.
What is the timescale of early land plant evolution?
The 4 key stages of land plant evolution started in the Ordovician period in the Palaeozoic era and continued through to the Cretaceous period in the Mesozoic era. The timescale of early land plant evolution spanned roughly 345 million years.
When did plants first evolve?
Plants first evolved over 3.7 billion years ago alongside all other life on earth, however the last common ancestor for all land plants is thought to have occurred 450 million years ago as plants made the jump to land in the Ordovician period.
