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[[Image:Abies alba 02.jpg|right|300px|thumb|A [[Silver Fir]] shoot showing three successive years of retained leaves]]  

[[Image:Abies alba 02.jpg|right|300px|thumb|A [[Silver Fir]] shoot showing three successive years of retained leaves]]  

In [[botany]], an '''evergreen''' plant is a plant that retains its [[leaf|leaves]] all year round, with each leaf persisting for more than 12 months. This contrasts with [[deciduous]] plants, which completely lose all their foliage for part of the year, becoming bare and leafless.

In [[botany]], an '''evergreen''' plant is a plant that retains its [[leaf|leaves]] all year round, with each leaf persisting for more than 12 months. This contrasts with [[deciduous]] plants, which completely lose all their foliage for part of the year, becoming bare and leafless.

[[Image:Liveoak 8231.JPG|left|thumb|A [[Southern live oak]] in winter]]

[[Image:Liveoak 8231.JPG|left|thumb|A [[Southern live oak]] in winter]]

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.

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.

===Reasons for being evergreen===

===Reasons for being evergreen===

In warm [[tropical]] regions, most [[rainforest]] plants are evergreen, 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. Most warm [[temperate climate]] plants are also evergreen. In cool temperate climates, fewer plants are evergreen, with a predominance of [[Pinophyta|conifers]], as few evergreen [[flowering plant|broadleaf]] plants can [[Psychrophile|tolerate severe cold]] below about -25 Â°C.

In warm [[tropical]] regions, most [[rainforest]] plants are evergreen, 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. Most warm [[temperate climate]] plants are also evergreen. In cool temperate climates, fewer plants are evergreen, with a predominance of [[Pinophyta|conifers]], as few evergreen [[flowering plant|broadleaf]] plants can [[Psychrophile|tolerate severe cold]] below about -25 °C.

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, even though their leaves and needles must be able to withstand cold and/or drought, and are thus less efficient at photosynthesis. In warmer areas, species such as some [[pine]]s and [[Cupressaceae|cypresses]] grow on poor soils and disturbed ground. 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. 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.

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, even though their leaves and needles must be able to withstand cold and/or drought, and are thus less efficient at photosynthesis. In warmer areas, species such as some [[pine]]s and [[Cupressaceae|cypresses]] grow on poor soils and disturbed ground. 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. 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.

* Aerts, R. (1995). The advantages of being evergreen.  ''Trends in Ecology & Evolution'' 10 (10): 402-407.

* Aerts, R. (1995). The advantages of being evergreen.  ''Trends in Ecology & Evolution'' 10 (10): 402-407.

* Ewers, F. W. & Schmid, R. (1981). Longevity of needle fascicles of ''Pinus longaeva'' (Bristlecone Pine) and other North American pines. ''Oecologia'' 51: 107-115.

* Ewers, F. W. & Schmid, R. (1981). Longevity of needle fascicles of ''Pinus longaeva'' (Bristlecone Pine) and other North American pines. ''Oecologia'' 51: 107-115.

* Matyssek, R. (1986) Carbon, water and nitrogen relations in evergreen and deciduous conifers. ''Tree Physiology'' 2: 177–187.

* Matyssek, R. (1986) Carbon, water and nitrogen relations in evergreen and deciduous conifers. ''Tree Physiology'' 2: 177–187.

* Sobrado, M. A. (1991) Cost-Benefit Relationships in Deciduous and Evergreen Leaves of Tropical Dry Forest Species. ''Functional Ecology'' 5 (5): 608-616.

* Sobrado, M. A. (1991) Cost-Benefit Relationships in Deciduous and Evergreen Leaves of Tropical Dry Forest Species. ''Functional Ecology'' 5 (5): 608-616.