tree form
Tree form is one of the three main elements by which a tree is defined. The others are tree species and tree size. Tree form is the form of a perennial plant, usually having secondary thickening, with a three-dimensional crown supported off the ground by a more or less trunk-like main stem or stems, so that the crown is typically sparse or absent near ground level. There is no minimum size for tree form (see bonsai, seedling).
This definition is abridged from A – Z of tree terms: A companion to British arboriculture. Order the book, read the preface.