When plants first lived on land, they did not exist as trees that towered over the land. In fact, the first land plants did not even grow to be more than an inch tall. But after millions of years of evolution, we now have the trees and flowers we have today. But how did plants evolve to take over the planet?
The first plants that arrived on land are called Bryophytes. Bryophytes can still be found today, but most people have never even noticed them. These plants did not evolve to have vascular tissue because there was no need for it since they lived in the ocean and did not need to stand on their own. Also, Bryophytes could not venture far into the land, because they needed a constant source of water present. Bryophytes also spent the majority of their life cycle in the gametophyte stage. This means the plants only had one set of chromosomes. The only time the Bryophytes have two sets of chromosomes are right before they released their spores for reproduction. However, the spores themselves only had one set of chromosomes, as well. The only part of the plant that contained two sets of chromosomes were the capsule that enclosed the spores before they were released. Moss that lives on land belongs to the Bryophyte phylum.
After a few million years, the Lycophytes evolved. While the Lycophytes still spent the majority of their life cycle in the gametophyte stage and produced spores, they were the first plants to evolve vascular tissue. This means for the first time ever plants could stand on their own. While they still had to stay close to water, Lycophytes adapted to be able to survive more inland than compared to the primitive Bryophytes. Club moss is an example of a Lycophyte, even though it is not a true moss.
Then Pterophytes evolved, and most people know these plants as ferns. These plants still needed water to be able to survive and reproduce, but was able to move much further inland. Pterophytes also spent about half their life cycle in the gametophyte stage, as well as half in the sporophyte stage. However, ferns still produced spores as their way of reproduction.
Gymnosperms, also known as conifers, evolved next. They were the first plants to produce seeds and spend the majority of their life cycle in the sporophyte stage. Gymnosperm seeds are referred to as “naked” seeds. They did not have fruit or flowers to help them disperse to new locations. However, they were the first plants to break their link with water and were able to survive anywhere on land that had enough water and nutrients to grow, as water was no longer needed for reproduction. Conifers were the first plants to evolve wood, which helped conserve water, as well as reinforced the plant, so it could grow much larger. Gymnosperms used the help of the wind to pollinate and spread their fertilized seeds to new territory.
The Angiosperms phylum is the most diverse plant phylum today and contains all plants that flowers or bears fruit. These plants were also the first to evolve a protective coat along their seeds. However, instead of using the wind, Angiosperms used animals and insects to pollinate their flowers, and produced fruit to help animals disperse their seeds to new locations. Their life cycle is spent in the sporophyte stage, except for their pollen and ovaries, just like the Gymnosperms. Grasses are even Angiosperms, as they have flowers even though they are sometimes difficult to see.
Freshwater plants used to be land plants that returned back to the water. However, instead of a marine environment, they now lived in a freshwater one.