Where Did Trees Come From?

Trees are considered to be an evolutionary descendant of ferns, one of the oldest types of plants currently around today. These early trees were much shorter than the average tree today and also reproduced with spores rather than seeds. The first known tree fossil dates back to about 385 million years ago during the Middle Devonian. During this time period, no plant grew higher than roughly waist height. However, in order to grow higher, plants would need to develop a stronger form of tissue.

The development of wood was a big evolutionary leap and took millions of years to accomplish. Wood is useful for several reasons. The most obvious is the structural support, but wood is also useful for allowing more efficient transport of water. With this new development, early trees could out-compete with their neighbors for precious sunlight and store more water to survive in droughts.

These early trees formed the backbone of Devonian and Carboniferous forests. This includes varieties like the Wattieza above, and their relatives the Lepidodendrales. The forests that grew and died during this period are the primary source material for all modern coal deposits. Without trees evolving at this time, the Industrial Revolution may have never happened! Even hundreds of millions of years ago, trees were laying the groundwork for modern human advancement.

These trees also grew fairly differently from modern trees. Instead of gradually growing continuously throughout its life, these plants stay at a low height for a while. Once it has built up sufficient resources, it will “rapidly” shoot up in height to rise above its neighbors and expose itself to lots of sunlight. Rapidly here means faster than a modern tree, but still slow to our eyes. Another difference is the quality of wood; ancient trees used a variety of wood that was easier to create but much less structurally sound. As a result, these trees could not grow very tall and did not have branches.

Trees were due for another evolutionary shift during the Triassic Period. Their method of reproduction shifted from spores to seeds. This is where we see the first example of a gymnosperm. Gymnosperm is Greek for ‘revealed seed’ or ‘naked seed.’ This class consists of many trees that we would recognize today, including any tree that has cones. Gymnosperms include cedars, Douglas-firs, cypresses, firs, junipers, kauri, larches, pines, hemlocks, redwoods, spruces, and yews. While gymnosperms became dominant in the Triassic Period, they first appeared sometime during the Carboniferous Period.

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