conifers
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Conifers are a group of cone-bearing seed plants, a subset of
gymnosperm The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers, cycads, '' Ginkgo'', and gnetophytes, forming the clade Gymnospermae. The term ''gymnosperm'' comes from the composite word in el, γυμν ...
s. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All extant conifers are
perennial A perennial plant or simply perennial is a plant that lives more than two years. The term ('' per-'' + '' -ennial'', "through the years") is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also wid ...
woody plants with secondary growth. The great majority are
tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that a ...
s, though a few are
shrub A shrub (often also called a bush) is a small-to-medium-sized perennial A perennial plant or simply perennial is a plant that lives more than two years. The term ('' per-'' + '' -ennial'', "through the years") is often used to differen ...
s. Examples include cedars, Douglas-firs, cypresses, firs, junipers, kauri,
larch Larches are deciduous conifers in the genus ''Larix'', of the family Pinaceae (subfamily Laricoideae). Growing from tall, they are native to much of the cooler temperate northern hemisphere, on lowlands in the north and high on mountains f ...
es,
pine A pine is any conifer 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 ...
s, hemlocks, redwoods, spruces, and yews.Campbell, Reece, "Phylum Coniferophyta". Biology. 7th. 2005. Print. P. 595 As of 1998, the division Pinophyta was estimated to contain eight families, 68 genera, and 629 living species. Although the total number of species is relatively small, conifers are ecologically important. They are the dominant plants over large areas of land, most notably the taiga of the
Northern Hemisphere The Northern Hemisphere is the half of Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sus ...
, but also in similar cool climates in mountains further south. Boreal conifers have many wintertime adaptations. The narrow conical shape of northern conifers, and their downward-drooping limbs, help them shed snow. Many of them seasonally alter their biochemistry to make them more resistant to freezing. While
tropical rainforest Tropical rainforests are rainforests that occur in areas of tropical rainforest climate in which there is no dry season The dry season is a yearly period of low rainfall, especially in the tropics. The weather in the tropics is domi ...
s have more
biodiversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic ('' genetic variability''), species In biology Biology is the scientific study of life ...
and turnover, the immense conifer forests of the world represent the largest terrestrial carbon sink. Conifers are of great economic value for softwood lumber and
paper Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, rags, grasses or other vegetable sources in water Water (chemical formula ) is an inorganic, transparent, tast ...
production.


Evolutionary history

The earliest conifers appear in the fossil record during the Late
Carboniferous The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonif ...
( Pennsylvanian), over 300 million years ago. Conifers have been suggested to be most closely related to the Cordaitales'','' a group of Carboniferous-Permian trees and clambering plants whose reproductive structures have some similarities to those of conifers. The most primitive conifers belong to the paraphyletic assemblage of " walchian conifers", which were small trees, and probably originated in dry upland habitats. The range of conifers expanded during the Early Permian ( Cisuralian) to lowlands due to increasing aridity. Walchian conifers were gradually replaced by more advanced voltzialean or "transition" conifers. Conifers were largely unaffected by the
Permian–Triassic extinction event The Permian–Triassic (P–T, P–Tr) extinction event, also known as the Latest Permian extinction event, the End-Permian Extinction and colloquially as the Great Dying, formed the boundary between the Permian and Triassic The Triassic ( ) ...
, and were dominant land plants of the
Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising ...
era. Modern groups of conifers emerged from the Voltziales during the Late Permian through
Jurassic The Jurassic ( ) is a geologic period The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the proce ...
. Conifers underwent a major decline in the
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'' ...
corresponding to the explosive
adaptive radiation In evolutionary biology Evolutionary biology is the subfield of biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coher ...
of
flowering plant Flowering plants are plants Plants are predominantly photosynthetic eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to t ...
s.


Taxonomy and naming

''Conifer'' is a Latin word, a compound of ''conus'' (cone) and ''ferre'' (to bear), meaning "the one that bears (a) cone(s)". The division name Pinophyta conforms to the rules of the '' International Code of Nomenclature for algae, fungi, and plants (ICN)'', which state (Article 16.1) that the names of higher taxa in plants (above the rank of family) are either formed from the name of an included family (usually the most common and/or representative), in this case Pinaceae (the
pine A pine is any conifer 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 ...
family), or are descriptive. A descriptive name in widespread use for the conifers (at whatever rank is chosen) is Coniferae (Art 16 Ex 2). According to the ''ICN'', it is possible to use a name formed by replacing the termination ''-aceae'' in the name of an included family, in this case preferably Pinaceae, by the appropriate termination, in the case of this division ''-ophyta''. Alternatively, " descriptive botanical names" may also be used at any
rank Rank is the relative position, value, worth, complexity, power, importance, authority, level, etc. of a person or object within a ranking, such as: Level or position in a hierarchical organization * Academic rank * Diplomatic rank * Hierarchy ...
above family. Both are allowed. This means that if conifers are considered a division, they may be called Pinophyta or Coniferae. As a class, they may be called Pinopsida or Coniferae. As an order they may be called Pinales or Coniferae or Coniferales. Conifers are the largest and economically most important component group of the gymnosperms, but nevertheless they comprise only one of the four groups. The division Pinophyta consists of just one class, Pinopsida, which includes both living and fossil taxa. Subdivision of the living conifers into two or more orders has been proposed from time to time. The most commonly seen in the past was a split into two orders, Taxales (Taxaceae only) and Pinales (the rest), but recent research into DNA sequences suggests that this interpretation leaves the Pinales without Taxales as paraphyletic, and the latter order is no longer considered distinct. A more accurate subdivision would be to split the class into three orders, Pinales containing only Pinaceae, Araucariales containing Araucariaceae and Podocarpaceae, and Cupressales containing the remaining families (including Taxaceae), but there has not been any significant support for such a split, with the majority of opinion preferring retention of all the families within a single order Pinales, despite their antiquity and diverse morphology. , the conifers were accepted as composed of seven families, with a total of 65–70 genera and 600–630 species (696 accepted names). The seven most distinct families are linked in the box above right and phylogenetic diagram left. In other interpretations, the Cephalotaxaceae may be better included within the Taxaceae, and some authors additionally recognize Phyllocladaceae as distinct from Podocarpaceae (in which it is included here). The family Taxodiaceae is here included in family Cupressaceae, but was widely recognized in the past and can still be found in many field guides. A new classification and linear sequence based on molecular data can be found in an article by Christenhusz et al.Christenhusz, M.J.M., Reveal, J., Farjon, A., Gardner, M.F., Mill, R.R. & Chase, M.W. (2011) A new classification and linear sequence of extant gymnosperms. Phytotaxa 19: 55–70. The conifers are an ancient group, with a
fossil A fossil (from Classical Latin Classical Latin is the form of Literary Latin recognized as a literary standard by writers of the late Roman Republic and early Roman Empire The Roman Empire ( la, Imperium Romanum ; grc-gre, ...
record extending back about 300 million years to the
Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick Adam Sedgwick (; 22 March 1785 – 27 January 1873) was a Briti ...
in the late
Carboniferous The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonif ...
period; even many of the modern genera are recognizable from fossils 60–120 million years old. Other classes and orders, now long extinct, also occur as fossils, particularly from the late Paleozoic and
Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising ...
eras. Fossil conifers included many diverse forms, the most dramatically distinct from modern conifers being some herbaceous conifers with no woody stems. Major fossil orders of conifers or conifer-like plants include the Cordaitales, Vojnovskyales, Voltziales and perhaps also the Czekanowskiales (possibly more closely related to the
Ginkgo ''Ginkgo'' is a genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as virus A virus is a submicroscopic infectious agent that replicates only inside ...
phyta). Multiple studies also indicate that the Gnetophyta belong within the conifers despite their distinct appearances, either placing them as a
sister group In phylogenetics In biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up ...
to Pinales (the 'gnepine' hypothesis) or as being more derived than Pinales but sister to the rest of the group. Most recent studies favor the 'gnepine' hypothesis.


Morphology

All living conifers are woody plants, and most are trees, the majority having monopodial growth form (a single, straight trunk with side branches) with strong apical dominance. Many conifers have distinctly scented resin, secreted to protect the tree against
insect Insects (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around pr ...
infestation and fungal infection of wounds. Fossilized resin hardens into
amber Amber is fossilized tree resin that has been appreciated for its color and natural beauty since Neolithic times. Much valued from antiquity to the present as a gemstone A gemstone (also called a fine gem, jewel, precious stone, or sem ...
. The size of mature conifers varies from less than one metre, to over 100 metres. The world's tallest, thickest, largest, and oldest living trees are all conifers. The tallest is a Coast Redwood (''Sequoia sempervirens''), with a height of 115.55 metres (although one Victorian mountain ash, '' Eucalyptus regnans'', allegedly grew to a height of 140 metres, although the exact dimensions were not confirmed). The thickest, meaning the tree with the greatest trunk diameter, is a Montezuma Cypress (''Taxodium mucronatum''), 11.42 metres in diameter. The largest tree by three-dimensional volume is a Giant Sequoia ('' Sequoiadendron giganteum''), with a volume 1486.9 cubic metres. The smallest is the pygmy pine (''Lepidothamnus laxifolius'') of New Zealand, which is seldom taller than 30 cm when mature. The oldest is a Great Basin Bristlecone Pine ('' Pinus longaeva''), 4,700 years old.


Foliage

Since most conifers are evergreens, the leaves of many conifers are long, thin and have a needle-like appearance, but others, including most of the Cupressaceae and some of the Podocarpaceae, have flat, triangular scale-like leaves. Some, notably '' Agathis'' in Araucariaceae and '' Nageia'' in Podocarpaceae, have broad, flat strap-shaped leaves. Others such as '' Araucaria columnaris'' have leaves that are awl-shaped. In the majority of conifers, the leaves are arranged spirally, exceptions being most of Cupressaceae and one genus in Podocarpaceae, where they are arranged in decussate opposite pairs or whorls of 3 (−4). In many species with spirally arranged leaves, such as '' Abies grandis'' (pictured), the leaf bases are twisted to present the leaves in a very flat plane for maximum light capture. Leaf size varies from 2 mm in many scale-leaved species, up to 400 mm long in the needles of some pines (e.g. Apache Pine, '' Pinus engelmannii''). The
stoma In botany, a stoma (from Greek ''στόμα'', "mouth", plural "stomata"), also called a stomate (plural "stomates"), is a pore found in the epidermis of leaves, stems, and other organs, that controls the rate of gas exchange. The pore is ...
ta are in lines or patches on the leaves and can be closed when it is very dry or cold. The leaves are often dark green in colour, which may help absorb a maximum of energy from weak sunshine at high latitudes or under forest canopy shade. Conifers from hotter areas with high sunlight levels (e.g. Turkish Pine '' Pinus brutia'') often have yellower-green leaves, while others (e.g. blue spruce, ''Picea pungens'') may develop blue or silvery leaves to reflect
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength In physics Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the re ...
light. In the great majority of genera the leaves are
evergreen 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 In the ...
, usually remaining on the plant for several (2–40) years before falling, but five genera ('' Larix'', '' Pseudolarix'', '' Glyptostrobus'', '' Metasequoia'' and '' Taxodium'') are
deciduous In the fields of horticulture and Botany, the term ''deciduous'' () means "falling off at maturity" and "tending to fall off", in reference to tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually ...
, shedding their leaves in autumn. The seedlings of many conifers, including most of the Cupressaceae, and ''Pinus'' in Pinaceae, have a distinct juvenile foliage period where the leaves are different, often markedly so, from the typical adult leaves.


Tree ring structure

Tree rings are records of the influence of environmental conditions, their anatomical characteristics record growth rate changes produced by these changing conditions. The microscopic structure of conifer wood consists of two types of cells: parenchyma, which have an oval or polyhedral shape with approximately identical dimensions in three directions, and strongly elongated tracheids. Tracheids make up more than 90% of timber volume. The tracheids of earlywood formed at the beginning of a
growing season A season A season is a division of the year based on changes in weather, ecology Ecology () is the study of the relationships between living organisms, including human Humans (''Homo sapiens'') are the most abundant and wides ...
have large radial sizes and smaller, thinner
cell wall A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biolo ...
s. Then, the first tracheids of the transition zone are formed, where the radial size of cells and thickness of their cell walls changes considerably. Finally, the latewood tracheids are formed, with small radial sizes and greater cell wall thickness. This is the basic
pattern A pattern is a regularity in the world, in human-made design, or in abstract ideas. As such, the elements of a pattern repeat in a predictable manner. A geometric pattern is a kind of pattern formed of geometric shapes and typically repeated ...
of the internal cell structure of conifer tree rings.


Reproduction

Most conifers are monoecious, but some are subdioecious or
dioecious Dioecy (; ; adj. dioecious , ) is a characteristic of a species, meaning that it has distinct individual organisms (unisexual) that produce male or female gametes, either directly (in animals) or indirectly (in seed plants). Dioecious reproduct ...
; all are wind-pollinated. Conifer seeds develop inside a protective cone called a
strobilus A strobilus (plural: strobili) is a structure present on many land plant Plants are predominantly photosynthetic eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular or ...
. The cones take from four months to three years to reach maturity, and vary in size from 2 mm to 600 mm long. In Pinaceae, Araucariaceae, Sciadopityaceae and most Cupressaceae, the cones are woody, and when mature the scales usually spread open allowing the seeds to fall out and be dispersed by the
wind Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few ...
. In some (e.g. firs and cedars), the cones disintegrate to release the seeds, and in others (e.g. the
pine A pine is any conifer 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 ...
s that produce pine nuts) the nut-like seeds are dispersed by
bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, ...
s (mainly nutcrackers, and jays), which break up the specially adapted softer cones. Ripe cones may remain on the plant for a varied amount of time before falling to the ground; in some fire-adapted pines, the seeds may be stored in closed cones for up to 60–80 years, being released only when a fire kills the parent tree. In the families Podocarpaceae, Cephalotaxaceae, Taxaceae, and one Cupressaceae genus ('' Juniperus''), the scales are soft, fleshy, sweet, and brightly colored, and are eaten by fruit-eating birds, which then pass the seeds in their droppings. These fleshy scales are (except in ''Juniperus'') known as arils. In some of these conifers (e.g. most Podocarpaceae), the cone consists of several fused scales, while in others (e.g. Taxaceae), the cone is reduced to just one seed scale or (e.g. Cephalotaxaceae) the several scales of a cone develop into individual arils, giving the appearance of a cluster of berries. The male cones have structures called microsporangia that produce yellowish pollen through meiosis. Pollen is released and carried by the wind to female cones. Pollen grains from living pinophyte species produce pollen tubes, much like those of angiosperms. The
gymnosperm The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers, cycads, '' Ginkgo'', and gnetophytes, forming the clade Gymnospermae. The term ''gymnosperm'' comes from the composite word in el, γυμν ...
male gametophytes (pollen grains) are carried by wind to a female cone and are drawn into a tiny opening on the ovule called the micropyle. It is within the ovule that pollen-germination occurs. From here, a pollen tube seeks out the female gametophyte, which contains archegonia each with an egg, and if successful, fertilization occurs. The resulting zygote develops into an
embryo An embryo is an initial stage of development of a multicellular organism. In organism In biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that ti ...
, which along with the female gametophyte (nutritional material for the growing embryo) and its surrounding integument, becomes a
seed A seed is an embryonic plant Plants are predominantly photosynthetic eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong t ...
. Eventually, the seed may fall to the ground and, if conditions permit, grow into a new plant. In forestry, the terminology of
flowering plant Flowering plants are plants Plants are predominantly photosynthetic eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to t ...
s has commonly though inaccurately been applied to cone-bearing trees as well. The male cone and unfertilized female cone are called ''male flower'' and ''female flower'', respectively. After fertilization, the female cone is termed ''fruit'', which undergoes ''ripening'' (maturation). It was found recently that the
pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gameto ...
of conifers transfers the
mitochondria A mitochondrion (; ) is an organelle found in the cells of most Eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group ...
l
organelle In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a si ...
s to the
embryo An embryo is an initial stage of development of a multicellular organism. In organism In biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that ti ...
, a sort of meiotic drive that perhaps explains why '' Pinus'' and other conifers are so productive, and perhaps also has bearing on observed sex-ratio bias. File:Abies lasiocarpa 6972.JPG, Pinaceae: unopened female cones of subalpine fir (''Abies lasiocarpa'') Taxus baccata MHNT.jpg, Taxaceae: the fleshy aril that surrounds each seed in the European Yew (''Taxus baccata'') is a highly modified seed cone scale Immature fir cone.jpg, Pinaceae: pollen cone of a Japanese Larch (''Larix kaempferi'')


Life cycle

Conifers are heterosporous, generating two different types of spores: male microspores and female megaspores. These spores develop on separate male and female sporophylls on separate male and female cones. In the male cones, microspores are produced from microsporocytes by
meiosis Meiosis (; , since it is a reductional division) is a special type of cell division Cell division is the process by which a parent cell divides into two daughter cells. Cell division usually occurs as part of a larger cell cycle T ...
. The microspores develop into pollen grains, which are male gametophytes. Large amounts of pollen are released and carried by the wind. Some pollen grains will land on a female cone for pollination. The generative cell in the pollen grain divides into two haploid sperm cells by
mitosis In cell biology, mitosis () is a part of the cell cycle The cell cycle, or cell-division cycle, is the series of events that take place in a cell that cause it to divide into two daughter cells. These events include the duplication ...
leading to the development of the pollen tube. At fertilization, one of the sperm cells unites its haploid nucleus with the haploid nucleus of an egg cell. The female cone develops two ovules, each of which contains haploid megaspores. A megasporocyte is divided by meiosis in each ovule. Each winged pollen grain is a four celled male gametophyte. Three of the four cells break down leaving only a single surviving cell which will develop into a female multicellular gametophyte. The female gametophytes grow to produce two or more archegonia, each of which contains an egg. Upon fertilization, the diploid egg will give rise to the embryo, and a seed is produced. The female cone then opens, releasing the seeds which grow to a young
seedling A seedling is a young sporophyte A sporophyte () is the diploid multicellular stage in the life cycle of a plant Plants are predominantly photosynthetic eukaryote Eukaryotes () are organisms whose cells have a nucleus. ...
. # To fertilize the ovum, the male cone releases
pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gameto ...
that is carried on the wind to the female cone. This is
pollination Pollination is the transfer of pollen from an anther The stamen ( plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower A flower, sometimes known as a bloom or blossom, is the reproductive struc ...
. (Male and female cones usually occur on the same plant.) # The pollen fertilizes the female gamete (located in the female cone). Fertilization in some species does not occur until 15 months after pollination. # A fertilized female gamete (called a zygote) develops into an
embryo An embryo is an initial stage of development of a multicellular organism. In organism In biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that ti ...
. # A
seed A seed is an embryonic plant Plants are predominantly photosynthetic eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong t ...
develops which contains the embryo. The seed also contains the integument cells surrounding the embryo. This is an evolutionary characteristic of the Spermatophyta. # Mature seed drops out of cone onto the ground. # Seed germinates and seedling grows into a mature plant. # When the plant is mature, it produces cones and the cycle continues.


Female reproductive cycles

Conifer reproduction is synchronous with seasonal changes in temperate zones. Reproductive development slows to a halt during each winter season and then resumes each spring. The male
strobilus A strobilus (plural: strobili) is a structure present on many land plant Plants are predominantly photosynthetic eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular or ...
development is completed in a single year. Conifers are classified by three reproductive cycles that refer to the completion of female strobilus development from initiation to seed maturation. All three types of reproductive cycle have a long gap between
pollination Pollination is the transfer of pollen from an anther The stamen ( plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower A flower, sometimes known as a bloom or blossom, is the reproductive struc ...
and fertilization. One year reproductive cycle:The genera include '' Abies'', '' Picea'', '' Cedrus'', '' Pseudotsuga,'' '' Tsuga'', '' Keteleeria'' ''( Pinaceae)'' and '' Cupressus, Thuja, Cryptomeria,
Cunninghamia ''Cunninghamia'' is a genus of one or two living species of evergreen coniferous tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition o ...
'' and '' Sequoia ( Cupressaceae)''. Female strobili are initiated in late summer or fall in a year, then they overwinter. Female strobili emerge followed by pollination in the following spring. Fertilization takes place in summer of the following year, only 3–4 months after pollination. Cones mature and seeds are then shed by the end of that same year. Pollination and fertilization occur in a single growing season.Singh, H. 1978. Embryology of gymnosperms. Berlin, Gebruder Borntraeger. Two-year reproductive cycle:The genera includes ''
Widdringtonia ''Widdringtonia'' is a genus of coniferous trees in the Cupressaceae (Cupressaceae, cypress family). The name was Austrian botanist Stephan Endlicher's way of honouring an early expert on the coniferous forests of Spain, Capt. Samuel Edward Widdri ...
'', '' Sequoiadendron'' ('' Cupressaceae'') and most species of ''Pinus''. Female
strobilus A strobilus (plural: strobili) is a structure present on many land plant Plants are predominantly photosynthetic eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular or ...
initials are formed in late summer or fall then overwinter. Female strobili emerge and receive pollen in the first year spring and become conelets. The conelet goes through another winter rest and, in the spring of the 2nd year archegonia form in the conelet. Fertilization of the archegonia occurs by early summer of the 2nd year, so the pollination-fertilization interval exceeds a year. After fertilization, the conelet is considered an immature cone. Maturation occurs by autumn of the 2nd year, at which time seeds are shed. In summary, the 1-year and the 2-year cycles differ mainly in the duration of the pollination- fertilization interval. Three-year reproductive cycle: Three of the conifer species are
pine A pine is any conifer 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 ...
species ('' Pinus pinea'', '' Pinus leiophylla'', '' Pinus torreyana'') which have pollination and fertilization events separated by a 2-year interval. Female strobili initiated during late summer or autumn in a year, then overwinter until the following spring. Female strobili emerge then pollination occurs in spring of the 2nd year then the pollinated strobili become conelets in the same year (i.e. the second year). The female gametophytes in the conelet develop so slowly that the megaspore does not go through free-nuclear divisions until autumn of the 3rd year. The conelet then overwinters again in the free-nuclear female gametophyte stage. Fertilization takes place by early summer of the 4th year and seeds mature in the cones by autumn of the 4th year.


Tree development

The growth and form of a forest tree are the result of activity in the primary and secondary meristems, influenced by the distribution of photosynthate from its needles and the hormonal gradients controlled by the apical meristems (Fraser et al. 1964).Fraser, D.A.; Belanger, L.; McGuire, D.; Zdrazil, Z. 1964. Total growth of the aerial parts of a white spruce tree at Chalk River, Ontario, Canada. Can. J. Bot. 42:159–179. External factors also influence growth and form. Fraser recorded the development of a single white spruce tree from 1926 to 1961. Apical growth of the stem was slow from 1926 through 1936 when the tree was competing with herbs and
shrub A shrub (often also called a bush) is a small-to-medium-sized perennial A perennial plant or simply perennial is a plant that lives more than two years. The term ('' per-'' + '' -ennial'', "through the years") is often used to differen ...
s and probably shaded by larger trees. Lateral branches began to show reduced growth and some were no longer in evidence on the 36-year-old tree. Apical growth totaling about 340 m, 370 m, 420 m, 450 m, 500 m, 600 m, and 600 m was made by the tree in the years 1955 through 1961, respectively. The total number of needles of all ages present on the 36-year-old tree in 1961 was 5.25 million weighing 14.25 kg. In 1961, needles as old as 13 years remained on the tree. The ash weight of needles increased progressively with age from about 4% in first-year needles in 1961 to about 8% in needles 10 years old. In discussing the data obtained from the one 11 m tall white spruce, Fraser et al. (1964) speculated that if the photosynthate used in making apical growth in 1961 was manufactured the previous year, then the 4 million needles that were produced up to 1960 manufactured food for about 600,000 mm of apical growth or 730 g dry weight, over 12 million mm3 of wood for the 1961 annual ring, plus 1 million new needles, in addition to new tissue in branches, bark, and roots in 1960. Added to this would be the photosynthate to produce energy to sustain respiration over this period, an amount estimated to be about 10% of the total annual photosynthate production of a young healthy tree. On this basis, one needle produced food for about 0.19 mg dry weight of apical growth, 3 mm3 wood, one-quarter of a new needle, plus an unknown amount of branch wood, bark and roots. The order of priority of photosynthate distribution is probably: first to apical growth and new needle formation, then to buds for the next year's growth, with the cambium in the older parts of the branches receiving sustenance last. In the white spruce studied by Fraser et al. (1964), the needles constituted 17.5% of the over-day weight. Undoubtedly, the proportions change with time.


Seed-dispersal mechanism

Wind and animal dispersals are two major mechanisms involved in the dispersal of conifer seeds. Wind born seed dispersal involves two processes, namely; local neighborhood dispersal (LND) and long-distance dispersal (LDD). Long-distance dispersal distances range from from the source. Birds of the crow family,
Corvidae Corvidae is a cosmopolitan family Family (from la, familia) is a group of people related either by consanguinity Consanguinity ("blood relation", from Latin Latin (, or , ) is a classical language belonging to the Italic langua ...
, are the primary distributor of the conifer seeds. These birds are known to cache 32,000 pine seeds and transport the seeds as far as from the source. The birds store the seeds in the soil at depths of under conditions which favor germination.


Invasive species

A number of conifers originally introduced for forestry have become invasive species in parts of
New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Souther ...
, including radiata pine ('' Pinus radiata''), lodgepole pine ('' P. contorta''), Douglas fir (''Pseudotsuga mensiezii'') and European larch ('' Larix decidua''). In parts of
South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...
, maritime pine ('' Pinus pinaster''), patula pine ('' P. patula'') and radiata pine have been declared invasive species. These wilding conifers are a serious environmental issue causing problems for pastoral farming and for conservation. Radiata pine was introduced to Australia in the 1870s. It is "the dominant tree species in the Australian plantation estate""Fauna conservation in Australian plantation forests: a review"
, May 2007, D.B. Lindenmayer and R.J. Hobbs
– so much so that many Australians are concerned by the resulting loss of native wildlife habitat. The species is widely regarded as an environmental weed across southeastern and southwestern Australia and the removal of individual plants beyond plantations is encouraged.


Predators

At least 20 species of roundheaded borers of the family Cerambycidae feed on the wood of spruce, fir, and hemlock (Rose and Lindquist 1985).Rose, A.H.; Lindquist, O.H. 1985. Insects of eastern spruces, fir and, hemlock, revised edition. Gov’t Can., Can. For. Serv., Ottawa, For. Tech. Rep. 23. 159 p. (cited in Coates et al. 1994, cited orig ed 1977) Borers rarely bore tunnels in living trees, although when populations are high, adult beetles feed on tender twig bark, and may damage young living trees. One of the most common and widely distributed borer species in North America is the whitespotted sawyer (''Monochamus scutellatus''). Adults are found in summer on newly fallen or recently felled trees chewing tiny slits in the bark in which they lay eggs. The eggs hatch in about 2 weeks and the tiny
larva A larva (; plural larvae ) is a distinct juvenile form many animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able ...
e tunnel to the wood and score its surface with their feeding channels. With the onset of cooler weather, they bore into the wood making oval entrance holes and tunnel deeply. Feeding continues the following summer when larvae occasionally return to the surface of the wood and extend the feeding channels generally in a U-shaped configuration. During this time, small piles of frass extruded by the larvae accumulate under logs. Early in the spring of the second year following egg-laying, the larvae, about 30 mm long,
pupa A pupa ( la, pupa, "doll"; plural: ''pupae'') is the life stage of some insect Insects (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was o ...
te in the tunnel enlargement just below the wood surface. The resulting adults chew their way out in early summer, leaving round exit holes, so completing the usual 2-year life cycle.


Cultivation

Conifers – notably '' Abies'' (fir), '' Cedrus'', '' Chamaecyparis lawsoniana'' (Lawson's cypress), '' Cupressus'' (cypress), juniper, '' Picea'' (spruce), '' Pinus'' (pine), '' Taxus'' (yew), '' Thuja'' (cedar) – have been the subject of selection for ornamental purposes (for more information see the
silviculture Silviculture is the practice of controlling the growth, composition/structure, and quality of forest A forest is an area of land dominated by trees. Hundreds of definitions of forest are used throughout the world, incorporating factors suc ...
page). Plants with unusual growth habits, sizes, and colours are propagated and planted in parks and gardens throughout the world.


Conditions for growth

Conifers can absorb nitrogen in either the
ammonium The ammonium cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is consid ...
(NH4+) or
nitrate Nitrate is a polyatomic ion with the chemical formula . Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an ins ...
(NO3) form, but the forms are not physiologically equivalent. Form of nitrogen affected both the total amount and relative composition of the soluble nitrogen in white spruce tissues (Durzan and Steward 1967).Durzan, D.J.; Steward, F.C. 1967. The nitrogen metabolism of ''Picea glauca'' (Moench) Voss and ''Pinus banksiana'' Lamb. as influenced by mineral nutrition. Can. J. Bot. 45:695–710. Ammonium nitrogen was shown to foster arginine and amides and lead to a large increase of free guanidine compounds, whereas in leaves nourished by nitrate as the sole source of nitrogen guanidine compounds were less prominent. Durzan and Steward noted that their results, drawn from determinations made in late summer, did not rule out the occurrence of different interim responses at other times of the year. Ammonium nitrogen produced significantly heavier (dry weight) seedlings with higher nitrogen content after 5 weeks (McFee and Stone 1968)McFee, W.W.; Stone, E.L. 1968. Ammonium and nitrate as nitrogen sources for ''Pinus radiata ''and ''Picea glauca''. Soil Sci. Soc. Amer. Proc. 32(6):879–884. than did the same amount of nitrate nitrogen. Swan (1960)Swan, H.S.D. 1960. The mineral nutrition of Canadian pulpwood species. 1. The influence of nitrogen, phosphorus, potassium, and magnesium deficiencies on the growth and development of white spruce, black spruce, jack pine, and western hemlock seedlings grown in a controlled environment. Pulp Paper Res. Instit. Can., Montreal QC, Woodlands Res. Index No. 116, Tech. Rep. 168. 66 p. found the same effect in 105-day-old white spruce. The general short-term effect of nitrogen fertilization on coniferous seedlings is to stimulate shoot growth more so than root growth (Armson and Carman 1961).Armson, K.A.; Carman, R.D. 1961. Forest tree nursery soil management. Ont. Dep. Lands & Forests, Timber Branch, Ottawa ON. 74 p. Over a longer period, root growth is also stimulated. Many nursery managers were long reluctant to apply nitrogenous
fertilizer A fertilizer (American English American English, sometimes called United States English or U.S. English, is the set of varieties of the English language English is a West Germanic language of the Indo-European language family ...
s late in the growing season, for fear of increased danger of frost damage to succulent tissues. A presentation at the North American Forest Tree Nursery Soils Workshop at Syracuse in 1980 provided strong contrary evidence: Bob Eastman, President of the Western Maine Forest Nursery Co. stated that for 15 years he has been successful in avoiding winter “burn” to Norway spruce and white spruce in his nursery operation by fertilizing with 50–80 lb/ac (56–90 kg/ha) nitrogen in September, whereas previously winter burn had been experienced annually, often severely. Eastman also stated that the overwintering storage capacity of stock thus treated was much improved (Eastman 1980).Eastman, B. 1980. The Western Maine Forest Nursery Company. pp. 291–295 In Proc. of the North American Forest Tree Nursery Soils Workshop, July 28 – August 1, 1980, Syracuse, New York. Environment Canada, Canadian Forestry Service, USDA For. Serv. The concentrations of nutrients in plant tissues depend on many factors, including growing conditions. Interpretation of concentrations determined by analysis is easy only when a nutrient occurs in excessively low or occasionally excessively high concentration. Values are influenced by environmental factors and interactions among the 16 nutrient elements known to be essential to plants, 13 of which are obtained from the soil, including
nitrogen Nitrogen is the chemical element A chemical element is a species of atoms that have a given number of protons in their nuclei, including the pure substance consisting only of that species. Unlike chemical compounds, chemical element ...
,
phosphorus Phosphorus is a chemical element A chemical element is a species of atoms that have a given number of protons in their nuclei, including the pure substance consisting only of that species. Unlike chemical compounds, chemical elements ...
,
potassium Potassium is the chemical element with the symbol K (from Neo-Latin '' kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmo ...
,
calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar ...
,
magnesium Magnesium is a chemical element A chemical element is a species of atoms that have a given number of protons in their nuclei, including the pure substance consisting only of that species. Unlike chemical compounds, chemical elemen ...
, and
sulfur Sulfur (or sulphur in British English) is a chemical element with the Symbol (chemistry), symbol S and atomic number 16. It is abundance of the chemical elements, abundant, Polyvalency (chemistry), multivalent and nonmetallic. Under standard c ...
, all used in relatively large amounts (Buckman and Brady 1969).Buckman, H.O.; Brady, N.C. 1969. The Nature and Properties of Soils, 7th ed. Macmillan NY. 653 p. Nutrient concentrations in conifers also vary with season, age, and kind of tissue sampled, and analytical technique. The ranges of concentrations occurring in well-grown plants provide a useful guide by which to assess the adequacy of particular nutrients, and the ratios among the major nutrients are helpful guides to nutritional imbalances.


Economic importance

The softwood derived from conifers is of great economic value, providing about 45% of the world's annual lumber production. Other uses of the timber include the production of paper and plastic from chemically treated wood pulp. Some conifers also provide foods such as pine nuts and Juniper berries, the latter used to flavor gin.


References


Bibliography

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External links

* *
tolweb.org
Conifers


World list of conifer species from Conifer Database by A. Farjon in the Catalogue of Life

Tree browser for conifer families and genera via the Catalogue of Life

Royal Horticultural Society Encyclopedia of Conifers: A Comprehensive Guide to Cultivars and Species

DendroPress: Conifers Around the World
* {{Authority control Plant divisions Extant Pennsylvanian first appearances