A pine is any conifer in the genus Pinus () of the family Pinaceae. Pinus is the sole genus in the subfamily Pinoideae. The species are evergreen trees or shrubs with their leaves in bunches, usually of 2 to 5 needles. The seeds are carried on woody cones, with two seeds to each cone scale. Pines are widely distributed in the Northern Hemisphere; they occupy large areas of taiga (boreal forest), but are found in many habitats, including the Mediterranean Basin, and dry tropical forests in southeast Asia and Central America. Some are fire-resistant or fire-dependent. Pine trees provide one of the most extensively used types of timber. The pine nuts are used to make dishes such as pesto, while retsina wine is flavoured with pine resin.
Description
Tree Pine trees are evergreen, coniferous resinous trees (or, rarely, shrubs) growing 3–80 metres (10–260 feet) tall, with the majority of species reaching 15–45 m (50–150 ft) tall. The smallest are Siberian dwarf pine and Potosi pinyon, and the tallest is an 83.45 m (273.8 ft) tall sugar pine (Pinus lambertiana) located in Yosemite National Park. Pines are long lived and typically reach ages of 100–1,000 years, some even more. The longest-lived is the Great Basin bristlecone pine (Pinus longaeva). One individual in the White Mountains of California, dubbed "Methuselah", is among the world's oldest living organisms at around 4,800 years old. An older tree near Wheeler Peak, now cut down, was dated at 4,900 years old. The spirals of branches, needles, and cone scales are arranged in Fibonacci number ratios.
Bark The bark 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, from buds at the tip of the year's new shoot, but others are multinodal, producing two or more whorls of branches per year.
Foliage Pines have four types of leaf:
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 called fascicles. 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's growing tip is damaged (e.g. eaten by an animal), the needle fascicles just below the damage generate a stem-producing bud, which can then replace the lost growth tip.
Cones Pines are monoecious, having the male and female cones on the same tree. 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 their pollen. The female cones take 1.5–3 years (depending on species) to mature after pollination, 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. The seeds (pine nuts) are mostly small and winged, and are anemochorous (wind-dispersed). Some are larger, have only a vestigial wing, and are bird-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 example whitebark pine, 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 called serotiny. The most common form of serotiny is pyriscence, in which resin binds the cones shut until the resin is melted by a forest fire, for example in P. radiata and P. muricata. The seeds are then released after the fire, enabling them to colonise the burnt ground with minimal competition from other plants.
Naming The modern English name "pine" derives from Latin pinus, traced to the Indo-European base *pīt- 'resin'. 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 in Danish fyr and German Föhre. The genus Pinus was named by Carl Linnaeus in 1753. Pinus sylvestris, the Scots pine, was later chosen as the type species. Several other conifers are commonly known as pines, such as the Norfolk Island pine (Araucaria heterophylla); however, they belong to other genera.
Evolution
Fossil history The Pinaceae, the pine family, first appeared in the Jurassic period. The genus Pinus first appeared during the Early Cretaceous; the oldest verified fossil is Pinus yorkshirensis from the Hauterivian-Barremian boundary (~130-125 million years ago) from the Speeton Clay, England. However, there are possible records of the genus from the Jurassic.
External phylogeny Based on transcriptome analysis, Pinus is most closely related to the genus Cathaya, which in turn is closely related to the genus Picea, the spruces. These genera, with firs and larches, form the pinoid clade of the Pinaceae.
Internal phylogeny The evolutionary history of the genus Pinus has been complicated by hybridisation. Pines are prone to inter-specific breeding. Wind pollination, long life spans, overlapping generations, large population size, and weak reproductive isolation make breeding across species more likely. As the pines have diversified, gene transfer between different species has created a complex history of genetic relatedness. Research using large genetic datasets has clarified these relationships. Two 21st-century phylogenies are given below; the differences between them demonstrate these complications:
Taxonomy
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