Plants have been on land for a long time. In fact, they emerged about 50 million years before animals emerged from the oceans. Early land plants were small and primitive compared to the towering giants and beautiful colors we see today. Throughout history there were four major periods in land plant development. The specific environments fostered the adaptations that allowed plants to cover the globe. So what is the story of land plants? Let’s get into it!
Plants first arrived on land around 450 million years ago during the Ordovician period. These plants were very small because they didn’t have the systems to pump water through their bodies, so they needed to stay low to the ground. This is also before the evolution of seeds, so the plants depended upon the presence of water to spread their gametes for reproduction. Examples of these kinds of plants that you can find today are mosses and liverworts. This period is also characterized by a diverse array of invertebrate life in the oceans, but there aren’t any fossils of animals on land at this time.
As the plants became more diversified and increased in numbers, the plants needed to adapt to gain an advantage for light and water. In the late Ordovician period is when vascular systems evolved. This allowed the plants to begin to grow up off the ground and to carry the water up to their cells to facilitate their functions including cellular respiration. Growing up meant they also had to grow down. To support the vertical growth and increased demand for water, plants began to develop roots to not only help anchor them in place, but also absorb more water. A plant that is a descendant of this next stage in land plants are ferns. This is still before seeds were evolved though, and the method of reproduction for these plants were spores, that still depend heavily on the presence of water.
The evolution of seeds was a big advancement for land plants. They decreased their need for water, had a protective coating on them, were more easily dispersible, and allowed the packaged genetic material to wait until the conditions were just right for growth. Seeds first evolved 390 million years ago in the Devonian period in gymnosperms, or plants that produce cones like evergreen trees.
The final adaptation that allowed plants to dominate the land was the evolution of flowers. About 120 million years ago In the Cretaceous period, plants developed flowers with male and female parts. The adaptation of pollination allowed plants to be able to reproduce with other plants that are not immediately next to them, allowing them to migrate more and more around the globe. The evolution of angiosperms, or flowering plants, also coincided with the evolution of pollinators. Plants developed colorful flowers, strong smells, and tasty fruits all in an effort to attract the pollinators to spread their genetic material. Although some pollen producing plants don’t need to go through all that effort because they just use the wind instead. Interestingly, it's the pollen from plants that use wind to spread that causes our seasonal allergies, because that is the one we breathe in the air.
The story of land plants is epic. They emerged on land before animals, and helped to create the environment hospitable for our existence today. They began to grow tall to compete for the sun, they developed a vascular system and roots to stay hydrated and support their increasing size, and seeds to spread across the globe. They even evolved alongside pollinators and used us animals to their benefit. The story of plants is part of the story of the earth and the life that is on it.