Trees are not a monophyletic taxonomic group but consist of a wide variety of plant species that have independently evolved a trunk and branches as a way to tower above other plants to compete for sunlight. The majority of tree species are angiosperms or hardwoods; of the rest, many are gymnosperms or softwoods.
A tree is a woody plant that regularly renews its growth. Most plants classified as trees have a single self-supporting trunk containing woody tissues, and in most species the trunk produces secondary limbs, called branches.
Colorado's major tree species include bristlecone pine, Colorado blue spruce, Douglas-fir, Engelmann spruce, limber pine, lodgepole pine, narrowleaf cottonwood, quaking aspen, piñon pine, plains cottonwood, ponderosa pine, Rocky Mountain juniper, subalpine fir and white fir.
The crown of the tree is made up of the leaves and branches. The trunk of the tree supports the crown and serves as a highway for food made in the leaves to travel to the roots and for water and nutrients from the roots to travel to the leaves.
In general, a plant is considered a tree if its height reaches more than 13 feet, lives for many years, and has a woody stem. Moreover, there are certain features which are common in trees.