In botany, an evergreen plant is a plant having leaves all year round. For the tree known as Silver Fir in western North America see Abies concolor. Botany, plant science(s, phytology, or plant biology is a branch of Biology and is the scientific study of plant Life In Botany, a leaf is an above-ground Plant organ specialized for Photosynthesis. This contrasts with deciduous plants, which completely lose their foliage for part of the year. Botany Autumn leaf color. See --> In Botany and Horticulture, deciduous Plants, including In Botany, a leaf is an above-ground Plant organ specialized for Photosynthesis.
Leaf persistence in evergreen plants may vary from a few months (with new leaves constantly being grown and old ones shed), to several decades (over thirty years in Great Basin Bristlecone Pine Pinus longaeva ). The Great Basin Bristlecone Pine ( Pinus longaeva) is one of the Bristlecone pines a group of three species of Pine found in the higher Mountains
One additional special case exists in Welwitschia, an African gymnosperm plant which produces only two leaves, which grow continuously throughout the plant's life but gradually wear away at the apex, giving about 20–40 years' persistence of leaf tissue. Quercus virginiana, also known as the Southern Live Oak, is an evergreen or nearly evergreen Oak Tree native to the southeastern Welwitschia is a monotypic Genus of Gymnosperm Plant, composed solely of the very distinct Welwitschia mirabilis. Gymnosperm (Gymnospermae are a group of Spermatophyte seed-bearing Plants with Ovules on the edge or blade of an open Sporophyll, which are In Botany, a leaf is an above-ground Plant organ specialized for Photosynthesis. In Botany, a leaf is an above-ground Plant organ specialized for Photosynthesis.
There are many different types of evergreens, both trees and shrubs, including most species of: conifers (e. g. white/scots/jack pine, red cedar, blue spruce), holly, hemlock, 'ancient' gymnosperms like cycads, rainforest trees and Eucalypts. There are three main subgenera of '''''Pinus''''', the subgenus Strobus ( White pines or soft pines the subgenus Ducampopinus ( The Scots Pine ( Pinus sylvestris L family Pinaceae) is a species of Pine native to Europe and Asia, ranging from The Jack Pine ( Pinus banksiana) is a North American Pine with its native range in Canada east of the Rocky Mountains from Western redcedar ( Thuja plicata) is a species of Thuja, an Evergreen coniferous Tree in the cypress family Picea pungens ( Colorado Blue Spruce or Blue Spruce) is a species of Spruce native to western North America, from southeast Holly ( Ilex) is a Genus of about 600 Species of Flowering plants in the family Aquifoliaceae, and the only Tsuga (from ツガ ja 栂 the name for Tsuga sieboldii) is a genus of conifers in the family Pinaceae. Cycads are a group of Seed plants characterized by a large crown of compound leaves and a stout trunk. Rainforests are Forests characterized by high Rainfall with definitions setting minimum normal annual rainfall between 1750–2000 mm (68-78 inches Eucalypts are woody plants belonging to three closely related genera Eucalyptus, Corymbia and Angophora.
Deciduous trees shed their leaves usually as an adaptation to a cold season or a dry season. Most tropical rainforest plants are evergreens, replacing their leaves gradually throughout the year as the leaves age and fall, whereas species growing in seasonally arid climates may be either evergreen or deciduous. Tropical rainforests are generally found near the Equator. They are common in Asia, Australia, Africa, South America, Central Most warm temperate climate plants are also evergreen. In cool temperate climates, fewer plants are evergreen, with a predominance of conifers, as few evergreen broadleaf plants can tolerate severe cold below about -30 °C. The flowering plants or angiosperms ( Angiospermae or Magnoliophyta) are the most widespread group Psychrophiles or Cryophiles (adj cryophilic are extremophilic Organisms that are capable of growth and reproduction in cold temperatures
In areas where there is a reason for being deciduous (e. g. a cold season or dry season), being evergreen is usually an adaptation to low nutrient levels. Deciduous trees lose nutrients whenever they lose their leaves, and they must replenish these nutrients from the soil to build new leaves. When few nutrients are available, evergreen plants have an advantage. In warmer areas, species such as some pines and cypresses grow on poor soils and disturbed ground. This article is about the tree For other uses of the term "pine" see Pine (disambiguation. The Cupressaceae or Cypress family is a Conifer family with worldwide distribution In Rhododendron, a genus with many broadleaf evergreens, several species grow in mature forests but are usually found on highly acidic soil where the nutrients are less available to plants. Rhododendron (from the Greek: rhodos, "rose" and dendron, "tree" is a genus of flowering plants in the family In taiga or boreal forests, it is too cold for the organic matter in the soil to decay rapidly, so the nutrients in the soil are less easily available to plants, thus favouring evergreens. Taiga (ˈtaɪgə from Turkic or Mongolian) is a Biome characterized by Coniferous forests
In temperate climates, evergreens can reinforce their own survival; evergreen leaf and needle litter has a higher carbon-nitrogen ratio than deciduous leaf litter, contributing to a higher soil acidity and lower soil nitrogen content. These conditions favour the growth of more evergreens and make it more difficult for deciduous plants to persist. In addition, the shelter provided by existing evergreen plants can make it easier for other evergreen plants to survive cold and/or drought. 
Owing to the botanical meaning, the idiomatic term "evergreen" refers to something that perpetually renews itself, or otherwise remains steady and constant (doesn't suddenly halt or "die off", as leaves on a deciduous tree. ) An evergreen market, for example, is one where there is a constant, renewed demand for an item or items, as opposed to a market which is expected to eventually saturate.