Pine

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

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 (two exceptions, Pinus leiophylla and Pinus lumholtzii, have deciduous sheaths).
• 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).

Phylogenetic evidence indicates that the subgenera diverged anciently from one another. Each subgenus is further divided into sections and subsections.

World Flora Online accepts 134 species-rank taxa (119 species and 15 nothospecies) of pines as current, with additional synonyms, and Plants of the World Online 126 species-rank taxa (113 species and 13 nothospecies), 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 (Asia and Europe). They occupy large areas of boreal forest (taiga) 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 5,200 m (17,100 ft), 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 (pine bolete) forms an ectomycorrhizal association with pines such as P. cembra, P. nigra, and P. sylvestris.

Uses

Timber

Pines are among the most commercially important tree species, valued for their timber and wood pulp throughout the world. In temperate and tropical regions, they are fast-growing softwoods that grow in relatively dense stands. Commercial pines are grown in plantations 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.

As pine wood has little resistance to insects or decay after logging, in its untreated state it is generally recommended for indoor construction purposes only, such as indoor drywall framing. It is commonly used in Canadian Lumber Standard graded wood. For outside use, pine needs to be treated with copper azole, chromated copper arsenate or other suitable chemical preservatives.

Ornamental uses

Many pine trees make attractive ornamental plantings for parks and larger gardens, while dwarf cultivars are suitable for smaller spaces. There are at least 818 named cultivars (or trinomials) recognised by the American Conifer Society ACS.

Food

The seeds (pine nuts) are generally edible; the young male cones can be cooked and eaten, as can the bark of young twigs. Some species have large pine nuts, which are harvested and sold for cooking and baking. They are an ingredient of pesto alla genovese.

The soft, moist, white inner bark (cambium) beneath the woody outer bark is edible and very high in vitamins A and C. It can be eaten raw in slices as a snack or dried and ground up into a powder for use as an ersatz flour or thickener in stews, soups, and other foods, such as bark bread. The use of pine cambium gave the Adirondack Indians their name, from the Mohawk Indian word atirú:taks, meaning "tree eaters".

A herbal tea is made by steeping young, green pine needles in boiling water (known as tallstrunt in Sweden). In eastern Asia, pine and other conifers are accepted among consumers as a beverage product, and used in teas, as well as wine. In Greece, the wine retsina is flavoured with resin from Pinus halepensis (Aleppo pine).

Other uses

Turpentine oil, traditionally used as a solvent in paints, resins and varnishes, is extracted from pine resin or pine wood. Pine needles are woven into baskets in Latin America. In traditional Chinese medicine, pine resin is used for burns, wounds and skin complaints. Chinese ink sticks for calligraphy are often made of pine soot, producing a matt black ink when mixed with water. Pine needles have been used by Latvian designer Tamara Orjola to create biodegradable products including paper, furniture, textiles and dyestuffs.

Culture

In ancient Egypt, the god Osiris was honoured with an image placed in a cavity inside a pine tree. In ancient Greece, the goddess Pitthea was linked with pines, while in ancient Rome, the tree was worshipped in the festival of the god Attis and the goddess Cybele. The Greek god of wine, Dionysus (also called Bacchus), was associated with pine as a symbol of fertility, and his devotees carried a stick topped with a pine cone (a thyrsus), a phallic symbol. The Buryat people of Siberia revered groves of Pinus sylvestris, while ancient Celtic Druids marked the midwinter solstice with fires of the same species.

In 1924, the Italian composer Ottorino Respighi completed his tone poem Pines of Rome. Each of its four movements depicts a pine-clad setting in the city of Rome, namely the Villa Borghese gardens, near a catacomb, on the Janiculum Hill, and along the Appian Way.

Pines are often featured in paintings. A 2021 study lists over a hundred works: many are by artists from the Mediterranean region, such as Paul Cézanne and Jean-Baptiste-Camille Corot; Northern Europe, such as Akseli Gallen-Kallela and James William Giles; and North America, with works by Tom Thomson and others. The paintings often depict Pinus pinea by the Mediterranean sea; other species include P. sylvestris and P. pinaster. The pine is a particular motif in Chinese art and literature, which sometimes combines painting and poetry in the same work. The pine symbolises longevity and steadfastness, as it retains its green needles throughout the year. Sometimes the pine and cypress are paired. At other times the pine, plum, and bamboo are considered as the "Three Friends of Winter".