World Flora Online accepts 134 species-rank taxa (119 species and 15nothospecies) of pines as current, with additional synonyms,[3] andPlants of the World Online 126 species-rank taxa (113 species and 13 nothospecies),[4] making it the largest genus among the conifers. The highest species diversity of pines is found in Mexico.[5][6][7] Pines are widelydistributed in theNorthern Hemisphere; they occupy large areas ofboreal forest, but are found in many habitats, including theMediterranean Basin, and dry tropical forests in southeast Asia and Central America.
Wood from pine trees is one of the most extensively used types oftimber, and some pines are widely used asChristmas trees.
Thebark of most pines is thick and scaly, but some species have thin, flaky bark. The branches are produced in "pseudo-whorls", actually a very tight spiral but appearing like a ring of branches arising from the same point. Many pines are uninodal, producing just one such whorl of branches each year, frombuds at the tip of the year's newshoot, but others are multinodal, producing two or more whorls of branches per year.[15]
Seed leaves (cotyledons) on seedlings are borne in a whorl of 4–24.
Juvenile leaves, which follow immediately on seedlings and young plants, are 2–6 centimetres (3⁄4–2+1⁄4 inches) long, single, green or often blue-green, and arranged spirally on the shoot. These are produced for six months to five years, rarely longer.
Scale leaves, similar to bud scales, are small, brown and not photosynthetic, and arranged spirally like the juvenile leaves.
Needles, the adult leaves, are green (photosynthetic) and bundled in clusters calledfascicles. The needles can number from one to seven per fascicle, but generally number from two to five. Each fascicle is produced from a small bud on a dwarf shoot in the axil of a scale leaf. These bud scales often remain on the fascicle as a basal sheath. The needles persist for 1.5–40 years, depending on species. If a shoot'sgrowing tip is damaged (e.g. eaten by an animal), the needle fascicles just below the damage will generate a stem-producing bud, which can then replace the lost growth tip.[15]
Pines aremonoecious, having the male and female cones on the same tree.[16]: 205 The male cones are small, typically 1–5 cm long, and only present for a short period (usually in spring, though autumn in a few pines), falling as soon as they have shed theirpollen. The female cones take 1.5–3 years (depending on species) to mature afterpollination, with actual fertilisation delayed one year. At maturity the female cones are 3–60 cm long. Each cone has numerous spirally arranged scales, with two seeds on each fertile scale; the scales at the base and tip of the cone are small and sterile, without seeds.[15]
The seeds are mostly small and winged, and areanemochorous (wind-dispersed), but some are larger and have only a vestigial wing, and arebird-dispersed. Female cones are woody and sometimes armed to protect developing seeds from foragers. At maturity, the cones usually open to release the seeds. In some of the bird-dispersed species, for examplewhitebark pine,[17] the seeds are only released by the bird breaking the cones open. In others, the seeds are stored in closed cones for many years until an environmental cue triggers the cones to open, releasing the seeds. This is calledserotiny. The most common form of serotiny is pyriscence, in which resin binds the cones shut until melted by a forest fire, for example inP. radiata andP. muricata; the seeds are then released after the fire to colonise the burnt ground with minimal competition from other plants.[15][18]
The modern English name "pine" derives from Latinpinus, traced to the Indo-European base*pīt- 'resin'.[19] Before the 19th century, pines were often called firs, a name now applied to another genus,Abies. In some European languages, Germanic cognates of the Old Norse name are still in use for pines, as inDanishfyr,Swedishfura/furu, andGermanFöhre.[20]
Pines aregymnosperms. The genus is divided into two subgenera based on the number offibrovascular bundles in the needle, and the presence or absence of a resin seal on the scales of the mature cones before opening. The subgenera can be distinguished by cone, seed, and leaf characters:
Pinus subg.Pinus, the yellow, or hard pine group, with cones with a resin seal on the scales, and generally with harder wood; the needle fascicles mostly have a persistent sheath (two exceptions,Pinus leiophylla andPinus lumholtzii, have deciduous sheaths).[15] The subgenus has also been calleddiploxylon, on account of its two fibrovascular bundles.[23]
Pinus subg.Strobus,syn.Pinus subg.Ducampopinus, the white, or soft pine, and pinyon pine groups, with cones without a resin seal on the scales, and usually have softer wood; the needle fascicles mostly have a deciduous sheath (one exception,Pinus nelsonii, has a persistent sheath).[15] The subgenus has also been calledhaploxylon, on account of its single fibrovascular bundle.[23]
Phylogenetic evidence indicates that both subgenera have a very ancient divergence from one another.[24] Each subgenus is further divided into sections and subsections.[25]
Many of the smaller groups ofPinus are composed of closely related species with recent divergence and history of hybridisation. This results in low morphological and genetic differences. This, coupled with low sampling and underdeveloped genetic techniques, has made taxonomy difficult to determine.[26] Recent research using large genetic datasets has clarified these relationships into the groupings often accepted today.[25]
Pinus is the largest genus of thePinaceae, the pine family, which first appeared in theJurassic period.[27] Based on recenttranscriptome analysis,Pinus is most closely related to the genusCathaya, which in turn is closely related to the genusPicea, the spruces. These genera, withfirs andlarches, form the pinoidclade of the Pinaceae.[24] Pines first appeared during the Early Cretaceous, with the oldest verified fossil of the genus beingPinus yorkshirensis from theHauterivian-Barremian boundary (~130-125 million years ago) from theSpeeton Clay, England.[28] However, there are possible records from the Jurassic.[29]
The evolutionary history of the genusPinus has been complicated byhybridisation. Pines are prone to inter-specific breeding. Wind pollination, long life spans, overlapping generations, large population size, and weakreproductive isolation make breeding across species more likely.[30] As the pines have diversified, gene transfer between different species has created a complex history of genetic relatedness.
Two recent phylogenies are given below; the differences between them, and other published phylogenies, demonstrate these complications:
Pines are native to theNorthern Hemisphere, and to a few parts from the tropics totemperate regions in theSouthern Hemisphere. Most regions of the Northern Hemisphere host somenative species of pines; they occupy large areas ofBoreal forest, and are found all around the Mediterranean Basin. The northernmost isScots pine, reaching just north of 70° N inStabbursdalen National Park in Norway;[32]Google Maps shows geolocated images with pines at 70° 09' N.[33] One species (Sumatran pine) crosses the equator in Sumatra to 2°S.[34] In North America, various species occur in regions at latitudes from as far north as 66° N[34] to as far south as 12°N.[35]
Pines may be found in a very large variety of environments, ranging from semi-arid desert to rainforests, from sea level up to 5,200 m (17,100 ft), from the coldest to the hottest environments on Earth. They often occur in mountainous areas with favourable soils and at least some water.[36]
Various species have been introduced to temperate andsubtropical regions of both hemispheres, where they are grown astimber or cultivated as ornamental plants in parks and gardens. A number of such introduced species have becomenaturalised, and some species are consideredinvasive in some areas[37] and threaten native ecosystems.
Pine beauty moth (Panolis flammea) on pine needlesPine hawk-moth (Sphinx pinastri) caterpillar feeding on pine needles
Pines grow well in acid soils, some also oncalcareous soils; most require good soil drainage, preferring sandy soils, but a few (e.g.lodgepole pine) can tolerate poorly drained wet soils. A few are able to sprout after forest fires (e.g.Canary Island pine). Some species of pines (e.g.Bishop pine) need fire to regenerate, and their populations slowly decline under fire suppression regimens.
Pine trees are beneficial to the environment since they can remove carbon dioxide from the atmosphere. Although several studies have indicated that after the establishment of pine plantations in grasslands, there is an alteration of carbon pools including a decrease of the soil organic carbon pool.[38]
Several species are adapted to extreme conditions imposed by elevation and latitude (e.g. Siberian dwarf pine,mountain pine, whitebark pine, and thebristlecone pines). The pinyon pines and a number of others, notablyTurkish pine andgray pine, are particularly well adapted to growth in hot, drysemidesert climates.[39]
Pinepollen may play an important role in the functioning ofdetritalfood webs.[40] Nutrients from pollen aid detritivores in development, growth, and maturation, and may enable fungi to decompose nutritionally scarce litter.[40] Pine pollen is also involved in moving plant matter between terrestrial and aquatic ecosystems.[40]
Pine needles serve as food for variousLepidoptera (butterfly andmoth) species. Several species of pine are attacked bynematodes, causingpine wilt disease, which can kill some quickly. Some of these Lepidoptera species, many of them moths, specialise in feeding on only one or sometimes several species of pine. Beside that many species of birds and mammals shelter in pine habitat or feed onpine nuts. The seeds are commonly eaten by birds, such as grouse, crossbills, jays, nuthatches, siskins, and woodpeckers, and bysquirrels. Some birds, notablynutcrackers andpinyon jays, are of major importance in distributing pine seeds to new areas. Pine needles are sometimes eaten by theSymphytan speciespine sawfly, andgoats.[41]
Pines are among the most commercially important tree species, valued for their timber andwood pulp throughout the world.[42][43] In temperate and tropical regions, they are fast-growingsoftwoods that grow in relatively dense stands. Commercial pines are grown inplantations for timber that is denser and therefore more durable than spruce (Picea). Pine wood is widely used in high-value carpentry items such as furniture, window frames, panelling, floors, and roofing due to its abundance and low-cost.[44]Turpentine is extracted from the wood of some species of pine.[45]
As pine wood has no insect- or decay-resistant qualities after logging, in its untreated state it is generally recommended for indoor construction purposes only (indoordrywall framing, for example). It is commonly used inCanadian Lumber Standard graded wood.[46] For outside use, pine needs to be treated with copper azole,chromated copper arsenate or other suitablechemical preservative.[47]
"Pine Clouds", 1903 painting on fan by Wu Ku-hsiang
Many pine species make attractive ornamental plantings forparks and largergardens with a variety of dwarfcultivars being suitable for smaller spaces. There are currently 818 namedcultivars (ortrinomials) recognised by theAmerican Conifer Society ACS.[48] Pines are also commercially grown and harvested forChristmas trees. Pine cones, among the largest and most durable of all conifer cones, are craft favourites. Pine boughs, appreciated especially in wintertime for their pleasant smell and greenery, are popularly cut for decorations.[49] Pine needles are also used for making decorative articles such as baskets, trays, pots, etc., and during theU.S. Civil War, the needles of thelongleaf pine "Georgia pine" were widely employed in this.[50] This originally Native American skill is now being replicated across the world. Pine needle handicrafts are made in the US, Canada, Mexico, Nicaragua, and India. Pine needles are also versatile and have been used by Latvian designer Tamara Orjola to create differentbiodegradable products including paper, furniture, textiles and dye.[51]
When grown forsawlogs, pine plantations can be harvested after 25 years, with some stands being allowed to grow up to 50 or more years (the wood value increases more quickly as the trees age). In colder and drier climates, growth is slower, and harvesting can be at much older ages. Imperfect trees (such as those with bent trunks or forks, smaller trees, or diseased trees) are removed in a "thinning" operation every 5–10 years. Thinning allows the best trees to grow faster, because it prevents weaker trees from competing for sunlight, water, and nutrients. Young trees removed during thinning are used for pulpwood or are left in the forest, while most older ones are good enough for saw timber.[52]
A 30-year-old commercial pine tree grown in good conditions inArkansas will be about 0.3 m (1 ft) in diameter and about 20 m (66 ft) high. After 50 years, the same tree will be about0.5 m (1+1⁄2 ft) in diameter and 25 m (82 ft) high, and its wood will be worth about seven times as much as the 30-year-old tree.This however depends on the region, species and silvicultural techniques. In New Zealand, a plantation's maximum value is reached after around 28 years with height being as high as 30 m (98 ft) and diameter0.5 m (1+1⁄2 ft), with maximum wood production after around 35 years (again depending on factors such as site, stocking and genetics). Trees are normally planted 3–4 m apart, or about 1,000 per hectare (100,000 per square kilometre).[53][54][55][56]
The seeds (pine nuts) are generally edible; the young male cones can be cooked and eaten, as can the bark of young twigs.[57] Some species have large pine nuts, which are harvested and sold for cooking and baking. They are an ingredient ofpesto alla genovese.[58]
The soft, moist, white inner bark (cambium) beneath the woody outer bark is edible and very high in vitaminsA andC.[48] It can be eaten raw in slices as a snack or dried and ground up into a powder for use as anersatz flour or thickener in stews, soups, and other foods, such asbark bread.[59] Adirondack Indians got their name from theMohawk Indian wordatirú:taks, meaning "tree eaters".[59]
Atea is made by steeping young, green pine needles in boiling water (known astallstrunt in Sweden).[59] In eastern Asia, pine and other conifers are accepted among consumers as a beverage product, and used in teas, as well as wine.[60] In Greece, the wineretsina is flavoured with Aleppo pine resin.[61]
A falling pine pictured in the coat of arms ofMyrskylä, a small town in Finland
Pines have been a frequently mentioned tree throughout history, including in literature, art, and in religious texts.
The pine is a particular motif in Chinese art and literature, which sometimes combines painting and poetry in the same work. Some of the main symbolic attributes of pines in Chinese art and literature are longevity and steadfastness: the pine retains its green needles through all the seasons. Sometimes the pine and cypress are paired. At other times the pine, plum, and bamboo are considered as the "Three Friends of Winter".[64]
Trees which may be pines or other conifers are mentioned in some verses of theBible. In theBook of Nehemiah 8:15, theKing James Version translates Hebrew "עץ שמן" (etz shman), 'oil tree', as pine,[73] and the unknown type of tree of Hebrew "תדהר" in Isaiah 60:13 similarly.[74] Some botanical authorities believe that the Hebrew word "ברוש" (bərōsh), "cypress", which is used many times in the Bible, properly designatesPinus halepensis, the Aleppo or Jerusalem pine, or inHosea 14:8[75] which refers to fruit,Pinus pinea, the stone pine.[76]The word used in modern Hebrew for pine is "אֹ֖רֶן" (oren), which occurs only in Isaiah 44:14,[77] but two manuscripts have "ארז" (cedar), a much more common word.[78]
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