Plant Evolution

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.

• Here, we'll delve into plant evolution.
• First, we'll define what is the evolution of plants.
• Then, we'll study the origin and evolution of plants.
• We'll continue with the enormous importance of plant evolution that changes the conditions on Earth forever.
• We'll also analyze the timeline of plant evolution.
• We'll finish with some examples of adaptions that plants developed through their evolution.

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.

• Diversity within populations and between individuals occurs naturally through genetic variation. A phenomenon where, thanks to differences in the DNA sequences from one individual to another (i.e. different allele frequencies), different morphological traits are present within a species. Genetic variation can be caused by mutations, sexual reproduction or genetic drift, but no matter the cause the outcome is always the same: slight differences between individuals.

• Some differences caused by genetic variation can be beneficial, or harmful, to an individual's chance of survival. What is beneficial varies across different periods, environments, and in the presence or absence of predators and resources. The environmental factors affecting survival are known as selection pressures.

• Left to time, populations may change to the point where they are no longer recognizable as descendants of their ancestors. These morphological changes are the result of a gradual change, over many generations, in the genetic makeup of a population.

This process is known as evolution. Natural selection is one of the mechanism by which evolution occurs.

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.

• This Last Universal Common Ancestor (LUCA) formed roughly 3.5 billion years ago.¹ LUCA gave rise to all living organisms we see today, plants, animals, fungi and bacteria alike.
• Early life forms were simple unicellular organisms, reliant on diffusion to gather all the energy and nutrients needed from their surrounding environment. With time, life evolved complex processes to make its own energy. This early cellular evolution underpinned the processes of glycolysis, respiration, and photosynthesis.²
• Photosynthesis is thought to have originated in bacteria and allowed organisms to harness sunlight for energy.³ Early plant ancestors, in the form of simple eukaryotic cells, are believed to have absorbed photosynthesizing cyanobacteria. These previously free-roaming cyanobacteria gave rise to chloroplasts, the photosynthetic organelles found in plants.

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.

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.