Pines are coniferous trees in the genus Pinus ( ), in the family Pinaceae. They make up the monotypic subfamily Pinoideae. There are about 115 species of pine, although different authorities accept between 105 and 125 species.

Distribution

Pines have been introduced in subtropical and temperate portions of the Southern Hemisphere, including Chile, Brazil, South Africa, Australia, and New Zealand, where they are grown widely as a source of timber, and some species are becoming invasive.

Morphology

Pines are evergreen and resinous trees (rarely shrubs) growing to 3–80 m tall, with the majority of species reaching between 15-45 m tall. The smallest are Siberian Dwarf Pine and Potosi Pinyon, and the tallest, Sugar Pine. Pines are long-lived, typically reaching ages of 100–1,000 years, some even more. The longest-lived is the Great Basin Bristlecone Pine Pinus longaeva, one individual of which at 4,840 years old in 2008 is one of the oldest living organisms in the world.

The bark of most pines is thick and scaly, but some species have thin, flaking 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. The spiral growth of branches, needles and cone scales are 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.

Foliage

• Seed leaves (cotyledons) on seedlings, borne in a whorl of 4-24.

• Juvenile leaves, which follow immediately on seedlings and young plants, 2-6 cm 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, small, brown and non-photosynthetic, and arranged spirally like the juvenile leaves.

• Needles, the adult leaves, which are green (photosynthetic), bundled in clusters (fascicles) of (1-) 2-5 (-6) needles together, each fascicle 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 is damaged (e.g. eaten by an animal), the needle fascicles just below the damage will generate a bud which can then replace the lost leaves.