What is a tree? How are trees different from grasses, sunflowers, dandelions, and other types of plants? And what do trees have in common with shrubs and woody vines? The answers to these questions seem obvious at first. But unless you are a botanist you may find that the answers don't come easily. Let's look a little closer to find some common characteristics of trees, shrubs, and woody vines.
Trees, shrubs, and vines belong to many different plant families. Some are closely related, like ponderosa pine and limber pine. Others are not closely related at all, like eastern red cedar and silver maple. However, trees, shrubs, and vines all have one thing that separates them from the rest of the plant world: a woody stem that is perennial or that lives for many years. Grasses and certain other plants may be perennial, but their tops are regrown year after year from rhizomes, bulbs, or other organs found at or just under the soil surface. (Continue Reading from Utah State University Forestry)
The vascular plant emerged around 400 million years ago and started Earth's forest-building process during the Silurian geologic period. Although not yet a "true" tree, this new member of the terrestrial plant kingdom became the perfect evolutionary link (and the largest plant species) with developing tree parts and considered the first proto-tree. Vascular plants developed the ability to grow large and tall with massive weight needed for the support of a vascular internal plumbing system. (Continue Reading from ThoughtCo.)