Woody trunk

Definition

Diagram of secondary growth in a eudicot or coniferous tree showing idealised vertical and horizontal sections. A new layer of wood is added in each growing season, thickening the stem, existing branches and roots.
Although “tree” is a term of common parlance, there is no universally recognised precise definition of what a tree is, either botanically or in common language.[2] In its broadest sense, a tree is any plant with the general form of an elongated stem, or trunk, which supports the photosynthetic leaves or branches at some distance above the ground.[3] Trees are also typically defined by height,[4] with smaller plants from 0.5 to 10 m (1.6 to 32.8 ft) being called shrubs,[5] so the minimum height of a tree is only loosely defined.[4] Large herbaceous plants such as papaya and bananas are trees in this broad sense.[2][6]

A commonly applied narrower definition is that a tree has a woody trunk formed by secondary growth, meaning that the trunk thickens each year by growing outwards, in addition to the primary upwards growth from the growing tip.[4][7] Under such a definition, herbaceous plants such as palms, bananas and papayas are not considered trees regardless of their height, growth form or stem girth. Certain monocots may be considered trees under a slightly looser definition;[8] while the Joshua tree, bamboos and palms do not have secondary growth and never produce true wood with growth rings,[9][10] they may produce “pseudo-wood” by lignifying cells formed by primary growth.[11] Tree species in the genus Dracaena, despite also being monocots, do have secondary growth caused by meristem in their trunk, but it is different from the thickening meristem found in dicotyledonous trees.[12]

Aside from structural definitions, trees are commonly defined by use; for instance, as those plants which yield lumber.[13]