All About the Evolution of Trees

Written by: Weston Justis

Trees are one of the most successful groups of living organisms on our planet. People often overlook the incredible complexity and uniqueness of these magnificent plants. Here, you will learn how trees have evolved into what they are today, as well as some of their unique biological characteristics.

It is only appropriate to start at the very beginning. Early in Earth's history, certain cyanobacteria could produce energy from H2O, CO2, and sunlight. Otherwise known as photosynthesis. Some Eukaryotic cells captured these cyanobacteria and, through endosymbiosis, developed a mutualistic relationship with the bacteria. These bacteria became the chloroplasts, which we know all plants have in common. This is also what happened with Mitochondria, which are organelles of plant cells as well.

For a while, plants still resided solely in water in the form of algae-like organisms. However, species that can take advantage of new environments and resources gain an edge in survivability. Thus, these green rugs gradually made their way onto dry land. Once in this new environment, height became the name of the game. Any plant that grew taller than its neighbors took more sunlight, starving those in its shadow. Since then, traits and abilities that enabled plants to grow taller and stronger have been heavily selected for.

Until now, plants were built mostly from cellulose, which is great for shape but not for strength. Over tens of millions of years, some plants achieved an evolutionary breakthrough with the development of lignin. Lignin is a strong macromolecule with a ring-shaped structure. This material could be combined with the cellulose inside plants to develop a stiff vertical structure (a stem). Of course, with the ability to grow taller, plants needed some serious piping improvements.

The first vascular plants appeared at the end of the Silurian Period, which lasted from 444 to 419 million years ago. These include lycophytes, ferns, and horsetails, and were the first to have vascular systems. A vascular system enables a plant to transport materials throughout its body after rising off the ground. It enabled further improvements in branch growth and stem height.

Of course, these plants were still diversifying and competing with each other, so they continued to go all out with lignin production, growing ever stiffer and taller. 380 million years ago, the first evidence of seed plants appeared. Seeds improved the plants’ ability to reproduce because they provided both protection and longevity to the plant gametes inside.

The carboniferous period, beginning about 360 million years ago, is where the first true trees show up. The woody stems of these new plants improved their ability to grow tall and transport water. These plants would be the first to look like trees today, occasionally reaching heights greater than 40 meters.

Gymnosperms, another glade of trees, are first seen in the fossil record about 360 million years ago as well. This group of trees evolved to not contain their seeds in an ovary or fruit. Pine trees, for example, have cones that house the female gametes. Modern-day gymnosperms include conifers, ginkgoes, and cycads. Ginkgo trees specifically are estimated to have risen about 200 million years ago, which is older than most dinosaurs. Pine trees are even younger, only seeming to show up about 150 million years ago.

Another major milestone in the evolution of trees is the angiosperms. This 120-million-year-old group is characterized by the presence of flowers and enclosed seeds. Flowers help with reproduction by attracting pollinating animals, and the enclosed seeds are useful in that they protect the embryo from harsh conditions. Flowering trees fall into this category. The youngest kinds of trees include maples and oaks, which are estimated to have evolved 67 million years ago and 56 million years ago, respectively.

As you may have been able to determine from everything discussed so far, trees are not a specific glade or taxonomic group but instead consist of many different groups of organisms that separately evolved a wood and a trunk to tower over other plants.

Today we have all sorts of trees. Trees with flowers, seeds, fruit, and ones that grow over 100 meters high! It is incredible to witness all of the way evolution and the need to photosynthesize have driven the diversification of such gigantic plants. Much more is still left to be discovered with regard to the hundreds of millions of years of fascinating tree evolution.