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In
botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the Ancient Greek wo ...

botany
, an evergreen is a plant which has foliage that remains green and functional through more than one growing season. This also pertains to plants that retain their foliage only in warm climates, and contrasts with
deciduous In the fields of horticulture Horticulture is the art of cultivating plants in gardens to produce food and medicinal ingredients, or for comfort and ornamental purposes. Horticulturists are agriculturists who grow flowers, fruits and nuts, ...
plants, which completely lose their foliage during the winter or dry season.


Evergreen species

There are many different kinds of evergreen plants, both
tree In botany, a tree is a perennial plant with an elongated Plant stem, stem, or trunk (botany), trunk, supporting branches and leaves in most species. In some usages, the definition of a tree may be narrower, including only wood plants with se ...

tree
s and
shrub A shrub (often called a bush) is a small- to medium-sized perennial A perennial plant or simply perennial is a plant Plants are predominantly photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the p ...

shrub
s. Evergreens include: *Most species of
conifers Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All exta ...

conifers
(e.g.,
pine A pine is any conifer Conifers are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The divi ...

pine
,
hemlock Hemlock may refer to: Plants *Several poisonous plants in the family Apiaceae **''Cicuta'' (water hemlock) **''Conium'', four species, of which ''maculatum'' is the only endemic outside of southern Africa; in history given to poison and execute p ...
,
blue spruce The blue spruce (''Picea pungens''), also commonly known as green spruce, white spruce, Colorado spruce, or Colorado blue spruce, is a species In biology, a species is the basic unit of biological classification, classification and a taxono ...
, and red cedar), but not all (e.g.,
larch Larches are deciduous In the fields of horticulture Horticulture is the art of cultivating plants in gardens to produce food and medicinal ingredients, or for comfort and ornamental purposes. Horticulturists grow flowers, fruits and nuts, v ...

larch
) *
Live oak Live oak or evergreen oak is any of a number of oaks in several different sections of the genus ''Quercus'' that share the characteristic of evergreen foliage. These oaks are not more closely related to each other than they are to other oaks. ...
,
holly ''Ilex'' (), or holly, is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classificati ...

holly
, and "ancient"
gymnosperm The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also ...
s such as
cycad :''For the insect, see Cicada.'' Cycads are seed plants that typically have a stout and woody (ligneous) trunk (botany), trunk with a crown (botany), crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious ...

cycad
s *Most
angiosperm Flowering plants include multiple members of the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ...

angiosperm
s from frost-free climates, such as
eucalypt Eucalypt is a descriptive name for woody plants with capsule fruiting bodies belonging to seven closely related genera (of the tribe Eucalypteae) found across Australasia: ''Eucalyptus'', ''Corymbia'', ''Angophora'', ''Stockwellia'', ''Allosyncarp ...

eucalypt
s and
rainforest Rainforests are characterized by a closed and continuous tree canopy Canopy may refer to: Plants * Canopy (biology), aboveground portion of plant community or crop (including forests) * Canopy (grape), aboveground portion of grapevine Religi ...

rainforest
trees * Clubmosses and relatives The Latin binomial term ''
sempervirens In botany, an evergreen is a plant which has foliage that remains green and functional through more than one growing season. This also pertains to plants that retain their foliage only in warm climates, and contrasts with deciduous plants, which ...
'', meaning "always green", refers to the evergreen nature of the plant, for instance :''
Cupressus sempervirens ''Cupressus sempervirens'', the Mediterranean cypress (also known as Italian cypress, Tuscan cypress, Persian cypress, or pencil pine), is a species of Cupressus, cypress native plant, native to the eastern Mediterranean region, in northeast Lib ...
'' (a cypress) :''
Lonicera sempervirens ''Lonicera sempervirens'' (commonly known as coral honeysuckle, trumpet honeysuckle, or scarlet honeysuckle) is a species of honeysuckle vine native to the eastern United States which is known for its reddish flowers. Description ''Lonicera semp ...

Lonicera sempervirens
'' (a honeysuckle) :''
Sequoia sempervirens ''Sequoia sempervirens'' ()''Sunset Western Garden Book,'' 1995:606–607 is the sole living species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a ...

Sequoia sempervirens
'' (a sequoia) Leaf longevity in evergreen plants varies from a few months to several decades (over thirty years in the
Great Basin Bristlecone Pine
Great Basin Bristlecone Pine
).


Evergreen families

Japanese umbrella pine is unique in that it has its own family of which it is the only species.


Differences between evergreen and deciduous species

Evergreen and deciduous species vary in a range of morphological and physiological characters. Generally, broad-leaved evergreen species have thicker leaves than deciduous species, with a larger volume of parenchyma and air spaces per unit leaf area. They have larger leaf biomass per unit leaf area, and hence a lower
specific leaf areaSpecific leaf area (SLA) is the ratio of leaf A leaf (plural leaves) is the principal lateral appendage of the vascular plant plant stem, stem, usually borne above ground and specialized for photosynthesis. The leaves and stem together form ...
. Construction costs do not differ between the groups. Evergreens have generally a larger fraction of total plant biomass present as leaves (LMF), but they often have a lower rate of photosynthesis.


Reasons for being evergreen or deciduous

Deciduous trees shed their leaves usually as an adaptation to a cold or dry/wet season. Evergreen trees do lose leaves, but each tree loses its leaves gradually and not all at once. Most
tropical rainforest Tropical rainforests are rainforest Rainforests are characterized by a closed and continuous tree canopy Canopy may refer to: Plants * Canopy (biology), aboveground portion of plant community or crop (including forests) * Canopy (grape ...

tropical rainforest
plants are considered to be 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. Most warm
temperate climate In geography Geography (from Ancient Greek, Greek: , ''geographia'', literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, and phenomena of the Earth and Solar System, plan ...
plants are also evergreen. In cool temperate climates, fewer plants are evergreen. In this climate, there is a predominance of
conifers Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All exta ...

conifers
because few evergreen
broadleaf
broadleaf
plants can tolerate severe cold below about . In areas where there is a reason for being deciduous, e.g. a cold season or dry season, evergreen plants are usually an adaptation of low nutrient levels. Additionally, they are usually sclerophyllous,(meaning hard-leaved) and have an excellent water economy due to scarce resources in the area in which they reside. The excellent water economy within the evergreen species is due to high abundance when compared to deciduous species. Whereas, deciduous trees lose nutrients whenever they lose their leaves. In warmer areas, species such as some
pine A pine is any conifer Conifers are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The divi ...

pine
s and
cypresses
cypresses
grow on poor soils and disturbed ground. In ''
Rhododendron ''Rhododendron'' (from Ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speakers simply as G ...

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 Taiga (; rus, тайга́, p=tɐjˈɡa; relates to Mongolic and Turkic Turkic may refer to: * anything related to the country of Turkey * Turkic languages, a language family of at least thirty-five documented languages ** Turkic alphabets (d ...

taiga
or
boreal forest Taiga (; rus, тайга́, p=tɐjˈɡa; relates to Mongolic languages, Mongolic and Turkic languages, Turkic languages), generally referred to in North America as a boreal forest or snow forest, is a biome characterized by pinophyta, conifero ...
s, 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 favoring evergreens. 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. This is the case with Mediterranean evergreen seedlings, which have unique C and N storages that allow stored resources to determine fast growth within the species, limiting competition and bolstering survival. These conditions favor 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 younger evergreen plants to survive cold and/or drought.


Threats to evergreens

A major threat to evergreen trees is the fungus ''Rhizosphere kalkhoffii,'' which causes the commonly green needles to appear brown or purple in color. This disease is called needle cast disease, and is widespread in Minnesota and other US states. This fungi spreads through splashing water to adjacent trees and needles. It has been found that needle infection occur at an average temperature of 25 degrees Celsius. Some particular trees are in fact resistant to the disease, such as Plant Norway (''P. abides'') or white spruce (''P. glaucid''), while others such as Colorado blue spruce (''Pica pungent'') are extremely at risk of contracting the disease. Preventative efforts to protect the evergreens include fungicide, mulch at the base of the tree and increased sprinkler control to prevent the water contamination. Within recent years, this detrimental disease has entered into Canada and provides challenges for commercial conifer tree growers (such as Christmas trees), and extensive research was conducted into possible fungicides for this disease with no clear cut option being presented. Therefore the future research regarding evergreen longevity is highly linked to additional counter measures to ''Rhizosphere kalkhoffii'' by looking at other fungicide potions.


See also

*
Semi-deciduousSemi-deciduous or semi-evergreen is a botanical term which refers to plant Plants are predominantly photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not ...
(semi-evergreen)


References


External links

* {{Cite Americana, wstitle=Evergreens, author=Helen Ingersoll , short=x Plants Botany