A peer-reviewed paper titled _Giant cladoxylopsid trees resolve the enigma of the Earth’s earliest forest stumps at Gilboa_ which was published in the reputable science magazine _Nature_ in 2007 claims to establish _Wattieza_ as the oldest example of a tree-like plant. This suggests **the earliest trees appeared in the Late Middle Devionian period which ended just over 380 million years ago**.



There are various approaches to classifying trees but here are some of the most common distinctions made:

* **Classification by Reproduction Mechanism**: Coniferous trees (from latin, roughly meaning cone-bearing) reproduce by releasing pollen from male cones which is carried through the wind to female cones in order to pollinate them. Once pollinated, the seeds are spread by wind, fire and wildlife. Non-coniferous trees, on the other hand, flower during spring and are pollinated by the help of a variety of mobile animals, most prominently bees. The pollinated seeds then develop into fruit that are eaten by animals which carry them from the original tree.
* **Classification by Leaf Replenishment**: Deciduous trees loose their leaves every year before a cold or dry season, whereas evergreen trees replenish their leaves gradually throughout the year. This difference has implications for the way in which these trees store their energy and grow with deciduous trees generally growing faster but having a shorter lifespan.
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