Conifers () are a group of Spermatophyte, a subset of . They are mainly evergreen trees with a regular branching pattern, reproducing with male and female conifer cone, usually monoecy. They are wind-pollinated and the seeds are usually dispersed by the wind.
Scientifically, they make up the phylum Pinophyta, also known as Coniferae. All Neontology conifers except for the Gnetophytes are perennial plant with secondary growth. There are over 600 living species.
Conifers first appear in the fossil record over 300 million years ago in the Carboniferous. They became dominant land plants in the Mesozoic, until flowering plants took over many ecosystems in the Cretaceous. Many conifers today are relict species, surviving in a small part of their former ranges. Such relicts include Wollemia, known only from a small area of Australia, and Metasequoia glyptostroboides, known from Cretaceous fossils and surviving in a small area of China.
Although the total number of species is relatively small, conifers are ecology important. They are the dominant plants over the taiga of the Northern Hemisphere. Boreal conifers have multiple adaptations to survive winters, including a conical shape to shed snow, strong tracheid vessels to tolerate ice pressure, and a waxy covering on the needle leaves to minimise water loss. Several fungi form associations with conifers. Other fungi cause diseases such as needle cast, especially harmful to young trees. Conifers are affected by pest insects such as wood-boring and by , which make galleries just under the bark. Conifers are of great economic value for timber and paper production.
Evolution
Fossil history
The earliest conifers appear in the fossil record during the Late
Carboniferous (Pennsylvanian) over 300 million years ago. Conifers are thought to be most closely related to the
Cordaitales , a group of extinct Carboniferous-Permian trees and clambering plants whose reproductive structures had some similarities to those of conifers. The most primitive conifers belong to the paraphyletic assemblage of "
Walchia", 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
Voltziales or "transition" conifers.
Conifers were largely unaffected by the Permian–Triassic extinction event,
and were dominant land plants of the
Mesozoic era. Modern groups of conifers emerged from the Voltziales during the Late Permian through
Jurassic.
Conifers underwent a major decline in the
Late Cretaceous corresponding to the explosive adaptive radiation of
.
File:Conifer fossil.jpg|Voltziales: Walchia foliage, Cisuralian, Germany
File:Araucaria mirabilis (fossil cone) (Jurassic; Argentina) (49021443726).jpg| Araucaria cone, Jurassic, Argentina
File:Elatides sp. (fossil conifer) (Judith River Group, Upper Cretaceous; Montana or Canada) (25210755717).jpg| Elatides foliage, Late Cretaceous, N. America
File:Σίγρι1.jpg|Base of conifer trunk with roots, Early Miocene, Lesbos, Greece
Relict species
Several
Neontology conifers have
relict taxon status, surviving in small areas or in very small numbers where they once may have been common and widespread. One such is
Wollemia nobilis, discovered in 1994 in some narrow, steep-sided,
sandstone in Australia.
The wild population consisted of under 60 adult trees with essentially no genetic variability, implying a genetic bottleneck some thousands of years ago.
The extant
consist of three relict genera, namely
Ephedra,
Gnetum, and
Welwitschia. Fossils definitely of the group date back to the
Late Jurassic, with many species in the Cretaceous.
Conifers as a whole, too, declined markedly after the angiosperms (flowering plants) diversified during the Cretaceous, coming to dominate most terrestrial ecosystems. Many conifer species became
Extinction, leaving 30 out of 80 genera with just one extant species, and 11 more with just two or three species. The popular phrase "
" could, the Dutch botanist
Aljos Farjon states, fittingly be applied to many of these. Thus,
Metasequoia glyptostroboides, the dawn redwood, is known from fossils of Late Cretaceous and
Miocene age, and was found also as an extant tree with a small relict range in China.
File:Wakehurst Place woodland Wollemi pine.jpg| Wollemia nobilis is a relict taxon known only from a small area in Australia.
File:Welwitschia at Ugab River basin.jpg| Welwitschia mirabilis is one of the , all relict taxa very unlike other conifers.
File:Metasequoia glyptostroboides Autumn leaf color.jpg| Metasequoia glyptostroboides survives in a small part of China, and is known from from the Late Cretaceous onwards.
External phylogeny
The cladogram summarizes the group's external phylogeny. The conifers are
, sister to a
clade consisting of the
Ginkgoidae and
Cycadidae.
Internal phylogeny
The
Gnetophyta, despite their distinct appearances, were long viewed as outside the conifer group, but phylogenomic analysis indicates that they are part of the conifer clade, sister to the pine family (the 'gnepine' hypothesis). If so, the gnetophytes once shared the distinctive characters of the conifers, and have lost them.
The cladogram summarizes the conifers' internal phylogeny:
Taxonomy
The name
conifer, meaning 'cone-bearing', derives from Latin laconus (cone) and ferre (to bear).
As recently as 1999, the botanist
Aljos Farjon wrote that while the Coniferae had up to the early 20th century been considered "a natural family",
comparable to the
Rosaceae, he doubted that the conifers or the gymnosperms formed natural groups (
).
By 2016, the conifers were recognised as a clade, with six families (not including the gnetophytes),
65–70 genera, and over 600 living species ().
Depending on interpretation, the
Cephalotaxaceae may or may not be included within the Taxaceae, while some authors recognize
Phyllocladus as distinct from Podocarpaceae. The family
Taxodiaceae is here included in the family Cupressaceae.
Description
All living conifers (except the gnetophytes) are woody plants, and most are trees with narrow leaves, often needle-like. There are separate male and female reproductive structures, the cones. Pollination is always by wind; the seeds are mostly winged. The trees have a regular branching pattern. Many conifers have distinctly scented
resin.
The world's tallest and oldest living trees are conifers. The tallest is a coast redwood (
Sequoia sempervirens), with a height of .
Among the smallest conifers is the pygmy pine (
Lepidothamnus laxifolius) of New Zealand, which is seldom taller than 30 cm when mature.
The oldest non-clonal living tree is a Great Basin bristlecone pine (
Pinus longaeva), 4,700 years old.
conifers have multiple
to survive winters, including the tree's conical shape to shed snow, strong tracheid vessels to tolerate ice pressure, and a waxy covering on the needle leaves to minimise water loss.
File:US 199 Redwood Highway.jpg|Tallest: Sequoia sempervirens can reach a height of .
Foliage
Most conifers are evergreens.
In many species such as pines, firs, and
cedrus, the
leaf are long, thin and needle-like. Others like
Cupressaceae have flat, triangular scale-like leaves.
In the majority of conifers, the leaves are arranged spirally, the exceptions being most of Cupressaceae and one genus in Podocarpaceae, where they are arranged in
Decussation opposite pairs or whorls of 3 or 4. In many species with spirally arranged leaves, such as
Abies grandis, 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
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
or under forest canopy shade. Conifers from lower latitudes 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 light. In the great majority of genera the leaves remain on the plant for several (2–40) years before falling, but five genera (
larch,
Pseudolarix,
Glyptostrobus,
Metasequoia and
Taxodium) are
deciduous, shedding their leaves in autumn.
The seedlings of some conifers, including pines, have a distinct juvenile foliage period where the leaves are different from the typical adult leaves.
File:20160118Pinus sylvestris1.jpg|Pinaceae: needle-like leaves of Scots pine ( Pinus sylvestris)
File:Araucaria Leaves.JPG|Araucariaceae: awl-like leaves of Cook pine ( Araucaria columnaris)
File:Abies grandis 5359.JPG|In Abies grandis and many other species with spirally arranged leaves, each leaf is twisted near its base to maximize light capture.
File:C lawsoniana Lge.jpg|Cupressaceae: scale leaves of Lawson's cypress ( Chamaecyparis lawsoniana); scale in mm
Wood
Conifer
xylem consists of two types of cells:
parenchyma, which have an oval or polyhedral shape, and strongly elongated
. Tracheids make up more than 90% of timber volume. The tracheids of earlywood formed at the beginning of a
growing season have large radial sizes and smaller, thinner
. Then, the first tracheids of the transition zone are formed, where the radial size of cells and the thickness of their cell walls changes considerably. Finally, latewood tracheids are formed, with small radial sizes and greater cell wall thickness. This is the basic pattern of the internal cell structure of conifer
.
File:Abies concolor tangential.jpg|Vertical (tangential) section of Abies concolor wood (xylem), showing as long overlapping tubes. Perforation pits (small circles) allow water to move from one tracheid to the next.
File:Report on the relation of railroads to forest supplies and forestry - together with appendices on the structure of some timber ties, their behavior, and the cause of their decay in the road bed, on (14755970324).jpg|Transverse section of wood, cutting across the tracheid tubes, showing of fast (big cells, earlywood) and slow seasonal growth
Reproduction
Conifers produce their seeds inside a
conifer cone called a strobilus. Most species are monoecious, with male and female cones on the same tree. All conifers are
Anemophily. In conifers such as pines, the cones are
, and when mature the scales usually spread open allowing the seeds, which are often winged, to fall out and be dispersed by the
wind. In others such as firs and cedars, the cones disintegrate to release the seeds.
Some conifers produce nut-like seeds, such as
, which are dispersed by
, in particular, nutcrackers, and
, which break up the cones.
(2025). 022638263X, University of Chicago Press. 022638263X
In fire-adapted pines such as
Pinus radiata, the seeds may be stored in closed cones for many years, being released only when a
Pyriscence.
Keith Rushforth (1987). 074702801X, Christopher Helm Publishers. 074702801X
In families such as
Taxaceae, the cone scales are much modified as edible
, resembling berries. These are eaten by fruit-eating birds, which then pass the seeds in their droppings.
File:Abies lasiocarpa 6972.JPG|Pinaceae: unopened female cones of Abies lasiocarpa ( Abies lasiocarpa)
File:Spotted nutcracker with pine nut (cropped).jpg|Northern nutcracker with nut of Pinus sibirica
Taxus baccata MHNT.jpg|Taxaceae: the fleshy aril that surrounds each seed in the Taxus baccata is a highly modified seed cone scale.
Japanese Larch pollen cone, Cardiff, Wales.jpg|Pinaceae: pollen cone of a Japanese larch ( Larix kaempferi)
Life cycle
Conifers are
heterosporous, generating two different types of spores: male
and female
.
These spores develop on separate male and female
sporophylls on separate male and female cones, usually on the same tree.
In the male cones, microspores are produced from microsporocytes by meiosis. The microspores develop into pollen grains, which contain the male (micro)gametophytes. Large amounts of pollen are released and carried by the wind. Some pollen grains land on female cones, pollinating them. The generative cell in the pollen grain divides into two haploid sperm cells by mitosis, 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. The female gametophytes grow to produce two or more haploid eggs. The fertilized egg, the (diploid) zygote, gives rise to the embryo, and a seed is produced. The female cone then opens, releasing the seeds which grow into . Some seedlings survive to grow into trees.
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 development is completed in a single year. Conifers have one of three reproductive cycles that differ in the time to complete female strobilus development from initiation to seed maturation. The cycle is one year in genera such as Abies, Picea, Cedrus, and Tsuga; two years in most pine species and in Sequoiadendron; and three years in three pine species including Pinus pinea. All three types have a long gap between pollination and fertilization.
Distribution and ecology
Conifers are the dominant plants over the
taiga forest of the Northern Hemisphere,
forming the world's largest terrestrial
biome. The taiga consists mainly of larches, pines, and spruces.
Larch is the most common tree in Russia, and by volume of timber, easily the most abundant tree genus worldwide.
The larch species
Larix gmelinii is the world's most northerly-growing tree, at 75° north in the
Taymyr Peninsula.
Conifers are widespread also in southern Europe, the
Middle East, the
Himalayas,
Southeast Asia, and Japan. Conifers are not confined to the Northern Hemisphere: around 200 conifer species live only in the tropics, and others live in Australasia, Africa (including Madagascar), and Central and South America.
Species richness decreases with latitude; a northern country like Canada has just 9 species, whereas Mexico has 43, and the tropical island of
New Caledonia has 42
Endemism species.
Since conifers cannot regrow their leaves rapidly like hardwoods, leaf diseases can seriously damage coniferous plantations, especially dense stands of young trees. Needle cast diseases, often caused by Ascomycota in the Rhytismataceae family, result in leaf fall.
At least 20 species of roundheaded wood-boring (Cerambycidae) feed on the wood of spruces, firs, and hemlocks.[Rose, A.H.; Lindquist, O.H. 1985. Insects of eastern spruces, fir and, hemlock, revised edition. Government of Canada, Canadian Forest Service, Ottawa, Forestry Technical Report 23.] (Scolytinae, in the Curculionidae) are destructive pests of commercial forestry; major pests of spruce and other conifers include Ips typographus in Eurasia[http://www.na.fs.fed.us/spfo/pubs/fidls/sprucebeetle/sprucebeetle.htm USFS Spruce Beetle]
The basidiomycete fungus Boletus pinophilus is among the fungi that form an ectomycorrhizal association with conifers, in its case with pines such as Pinus sylvestris.
Wilding conifer including Pinus radiata have become invasive species in New Zealand,
File:Siberian autumn in taiga..JPG|Taiga coniferous forest, mostly larches, pines, and spruces, covers a large area of Siberia (pictured) and Canada.
Economic importance
The
softwood derived from conifers is more easily worked than
hardwood from broadleaved (
angiosperm) trees. This makes it widely used and of great economic value, its many uses including construction, furniture, telegraph poles and fencing.
A large part of production is used for paper.
In the United Kingdom, the 48% of the woodland that is coniferous yields over 90% of the timber; the top species is
sitka spruce, yielding about half of the timber produced.
Worldwide, wood products reached a value of $100 billion by the end of the 20th century.
Conifers such as fir, cedar, cypress, juniper, spruce, pine, yew and Thuja have been selected by plant breeders for ornamental purposes. Plants with unusual growth habits, sizes, and colours are propagated and planted in parks and gardens throughout the world.
File:Young Sitka spruce plantation - geograph.org.uk - 949091.jpg|Forestry using sitka spruce
File:2016.04.12 18.14.33 DSC03322 - Flickr - andrey zharkikh.jpg| Globosa, an ornamental cultivar of Scots pine
File:JBP_Kotobuki.jpg| Pinus thunbergii 'Kotobuki'
as a 65-year-old bonsai
External links
