In botany, a tree is a perennial plant with an elongated stem, or trunk, supporting leaves or branches. In some usages, the definition of a tree may be narrower, including only woody plants, only plants that are usable as lumber or only plants above a specified height. At its broadest, trees include the taller palms, the tree ferns, bananas and bamboo. A tree typically has many secondary branches supported clear of the ground by the trunk. This trunk typically contains woody tissue for strength, and vascular tissue to carry materials from one part of the tree to another. For most trees it is surrounded by a layer of bark which serves as a protective barrier. Below the ground, the roots branch and spread out widely; they serve to anchor the tree and extract moisture and nutrients from the soil. Above ground, the branches divide into smaller branches and shoots. The shoots typically bear leaves, which capture light energy and convert it into chemical energy by photosynthesis, providing the food needed by the tree for its growth and development. Flowers and fruit may also be present, but some trees such as conifers instead have pollen cones and seed cones, and others such as tree ferns produce spores instead.