Pine

A pine is any conifer tree or shrub in the genus ''Pinus'' () of the family Pinaceae. ''Pinus'' is the sole genus in the subfamily Pinoideae. The World Flora Online created by the Royal Botanic Gardens, Kew and Missouri Botanical Garden accepts 187 species names of pines as current, together with more synonyms. The American Conifer Society (ACS) and the Royal Horticultural Society accept 121 species. Pines are commonly found in the Northern Hemisphere. ''Pine'' may also refer to the lumber derived from pine trees; it is one of the more extensively used types of lumber. The pine family is the largest conifer family and there are currently 818 named cultivars (or trinomials) recognized by the ACS.

Description

Pine trees are evergreen, coniferous resinous trees (or, rarely, shrubs) growing tall, with the majority of species reaching tall. The smallest are Siberian dwarf pine and Potosi pinyon, and the tallest is an tall ponderosa pine located in southern Oregon's Rogue River-Siskiyou National Forest.

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 (''P. longaeva''). One individual of this species, dubbed "Methuselah", is one of the world's oldest living organisms at around 4,800 years old. This tree can be found in the White Mountains of California. An older tree, now cut down, was dated at 4,900 years old. It was discovered in a grove beneath Wheeler Peak and it is now known as "Prometheus" after the Greek immortal.

The spiral growth of branches, needles, and cones scales may be arranged in Fibonacci number ratios. The new spring shoots are sometimes called "candles"; they are covered in brown or whitish bud scales and point upward at first, then later turn green and spread outward. These "candles" offer foresters a means to evaluate fertility of the soil and vigour of the trees.

Bark

The bark of most pines is thick and scaly, but some species have thin, flaky bark. The branches are produced in regular "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 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 will 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 fertilization 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 are mostly small and winged, and are anemophilous (wind-dispersed), but some are larger and 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 a resin binds the cones shut until melted by a forest fire, for example in '' P. rigida''.

Taxonomy

Pines are gymnosperms. The genus is divided into two subgenera based on the number of fibrovascular bundles in the needle. The subgenera can be distinguished by cone, seed, and leaf characters:
* ''Pinus'' subg. ''Pinus'', the yellow, or hard pine group, generally with harder wood and two or three needles per fascicle. The subgenus is also named ''diploxylon'', on account of its two fibrovascular bundles.
* ''Pinus'' subg. ''Strobus'', the white, or soft pine group. Its members usually have softer wood and five needles per fascicle. The subgenus is also named ''haploxylon'', on account of its one fibrovascular bundle.

Phylogenetic evidence indicates that both subgenera have a very ancient divergence from one another, having diverged during the late Jurassic. Each subgenus is further divided into sections and subsections.

Many of the smaller groups of ''Pinus'' are composed of closely related species with recent divergence and history of hybridization. This results in low morphological and genetic differences. This, coupled with low sampling and underdeveloped genetic techniques, has made taxonomy difficult to determine. Recent research using large genetic datasets has clarified these relationships into the groupings we recognize today.

Etymology

The modern English name "pine" derives from Latin ''pinus'', which some have traced to the Indo-European base ''*pīt-'' ‘resin’ (source of English ''pituitary''). Before the 19th century, pines were often referred to as firs (from Old Norse ''fura'', by way of Middle English ''firre''). In some European languages, Germanic cognates of the Old Norse name are still in use for pines — in Danish ''fyr'', in Norwegian ''fura/fure/furu'', Swedish ''fura/furu'', Dutch ''vuren'', and German ''Föhre'' — but in modern English, ''fir'' is now restricted to fir (''Abies'') and Douglas-fir (''Pseudotsuga'').

Phylogeny

''Pinus'' is the largest genus of the Pinaceae, the pine family, which first appeared in the Jurassic period. Based on recent Transcriptome analysis, ''Pinus'' is most closely related to the genus ''Cathaya'', which in turn is closely related to spruces. These genera, with firs and larches, form the pinoid clade of the Pinaceae. Pines first appeared during the Early Cretaceous, with the oldest verified fossil of the genus is ''Pinus yorkshirensis'' from the Hauterivian-Barremian boundary (131–129 million years ago) from the Speeton Clay

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