A tree is a perennial plant with an extended stem, or trunk, that supports branches and leaves in most species, according to botany. In certain cases, a tree’s definition may be limited, encompassing simply woody plants with secondary growth, trees that may be used as timber, or plants that are taller than a certain height. Taller palms, tree ferns, bananas, and bamboos are all trees in a broader sense. Trees are not a taxonomic category, but rather a collection of plant species that have evolved a trunk and branches to compete for sunlight by towering above other plants. Trees have a lengthy lifespan, with some reaching thousands of years. Trees have existed for about 370 million years. The world’s total number of mature trees is believed to be around three trillion.
Many secondary branches are supported clear of the ground by the trunk of a tree. Woody tissue for strength and vascular tissue to transport materials from one section of the tree to another make up the trunk. It is enclosed by a layer of bark that acts as a protective barrier for most trees. The roots branch out and stretch out extensively underneath the earth, anchoring the tree and extracting moisture and nutrients from the soil. The branches split into smaller branches and shoots above ground. The leaves on the shoots catch light energy and convert it to sugars through photosynthesis, giving nourishment for the tree’s growth and development.
Seeds are the most common way for trees to reproduce. Flowers and fruit may be present, but pollen cones and seed cones are found on some trees, such as conifers. Tree ferns, like palms, bananas, and bamboos, generate spores rather than seeds.
Trees have an important function in erosion control and climate regulation. They absorb carbon dioxide from the environment and store it in their tissues in huge amounts. Many animal and plant species rely on trees and forests for their survival. Tropical rainforests are among the world’s most biodiverse environments. Shade and shelter are provided by trees, as well as lumber for construction, fuel for cooking and heating, and fruit for sustenance. Forests are diminishing in certain parts of the world as trees are cut down to make more space accessible for agriculture. Trees have traditionally been respected for their lifespan and utility, with holy groves in numerous societies, and they play a role in many of the world’s myths.
Although “tree” is a popular term, neither botanically nor in common English, there is no widely accepted specific description of what a tree is. A tree, in the widest definition, is any plant that has an extended stem, or trunk, that supports photosynthetic leaves or branches at a height above the ground. The minimum height of a tree is only lightly defined, since lesser plants from 0.5 to 10 m (1.6 to 32.8 ft) are designated shrubs, hence the minimum height of a tree is only vaguely defined. In this sense, large herbaceous plants like papaya and bananas are trees.
A more specific explanation is that a tree’s woody trunk is generated through secondary growth, which means that the trunk thickens each year by expanding outwards in addition to the main upward growth from the growing tip. Herbaceous plants, such as palms, bananas, and papayas, are not considered trees under this classification, regardless of their height, growth type, or stem girth. While the Joshua tree, bamboos, and palms do not have secondary growth and never develop genuine wood with growth rings, they can develop “pseudo-wood” by lignifying cells created during primary development. Despite being monocots, tree species of the genus Dracaena exhibit secondary growth generated by meristem in their trunks, but it is not the same as the thickening meristem seen in dicotyledonous trees.
Aside from structural classifications, trees are frequently characterized by their usage; for example, as plants that produce timber.
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