Pine
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, 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 growing tall, with the majority of species reaching tall. The smallest are Siberian dwarf pine and Potosi pinyon, and the tallest is an tall sugar pine 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. 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 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 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, the needle fascicles just below the damage generate a stem-producing bud, which can then replace the lost growth tip.
Cones
The seeds are mostly small and winged, and are anemochorous. 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 ; 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 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
Pines are gymnosperms. The genus is divided into two subgenera based on the number of fibrovascular 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.
- 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.
World Flora Online accepts 134 species-rank taxa of pines as current, with additional synonyms, and Plants of the World Online 126 species-rank taxa, making it the largest genus among the conifers. The highest species diversity of pines is found in Mexico.
Distribution
Pines are native to the Northern Hemisphere, with the most species in North America, some in Asia, and a few in Europe. Only two species, Pinus sylvestris and Pinus sibirica, occur in more than one of those regions. They occupy large areas of boreal forest in latitudes between 50° and 60° N; about a third of this biome is in North America and Scandinavia, the rest in Siberia. The northernmost species is Scots pine, reaching just north of 70° N in Stabbursdalen National Park in Norway; One species, Pinus merkusii, crosses the equator in Sumatra to 2°S. In North America, various species occur in regions at latitudes from as far north as 66° N to as far south as 12°N.Various species have been introduced to temperate and subtropical regions of both hemispheres, where they are grown as timber or cultivated as ornamental plants in parks and gardens. A number of such introduced species have become naturalised, and species such as Pinus radiata are considered invasive in some regions.
Ecology
Environmental factors
Pines grow in a very large variety of environments, ranging from semi-arid desert to rainforests, from sea level up to, from the coldest to the hottest environments on Earth. They often occur in mountainous areas with favourable soils.Pinus contorta is a fire-dependent species, requiring wildfires to maintain healthy populations of diverse ages.
Pinus canariensis is highly fire-resistant, with adaptations such as growing epicormic sprouts after losing its needles in a fire. Some species such as Pinus muricata need fire to open their cones, allowing them to disperse their seeds. Other pines such as Pinus mugo and Pinus yunnanensis can grow at high elevation. Some pines, such as Pinus sabiniana, are adapted to growth in hot, dry semidesert climates.
Species interactions
Pine needles serve as food for the caterpillar larvae of several moth species including the pine beauty, a pest of mature stands of pine trees, and the pine hawk-moth, a large species which causes only occasional damage.Some moths, notably the pine processionary, whose caterpillars can completely defoliate pine trees, and the pine-tree lappet, are serious pests of commercial forestry.
Several species of pine are attacked by nematodes, causing pine wilt disease, which can quickly kill trees.
The sawfly Diprion pini is likewise a serious commercial pest of pine forestry, especially of Pinus sylvestris. Some birds such as nutcrackers are specialist feeders on pine seeds, and are important in distributing the seeds widely. Crossbills rely on Pinus sylvestris seeds in Scotland, and similarly help significantly to disperse the seeds, whereas red squirrels feed on the seeds but do little for seed dispersal. Pine pollen may contribute to food webs involving detritivores. Nutrients from pollen aid detritivores in development, growth, and maturation, and may enable fungi to decompose plant litter which is low in nutrients. The edible basidiomycete fungus Boletus pinophilus forms an ectomycorrhizal association with pines such as P. cembra, P. nigra, and P. sylvestris.