Pine trees of the genus pinus are resinous evergreen trees bearing seed cones and foliage in the form of needles. There are more than a hundred species of pine trees, about one-third of all conifers. They range throughout the northern hemisphere from Borneo to Scandanavia in Eurasia and from Mexico throughout Canada in North America.
Soft or white pines include the bristlecone, eastern white, lacebark and pinion and bristlecone pines among others
Hard or yellow pines include the loblolly, Jeffrey pine, shortleaf, slash and ponderosa pines among others.
Pines are also classified according to the number of needles on each needle-bearing scale. Some species have two needles on each scale, some have three and some have five. Those with two needles include the Aleppo, Corsican pine, cluster, Scots pine and stone pines. Pitch pines in America have three needles. And the stone pine of central Europe and the Weymouth pine have five leaves.
Pine tree seedlings bear a whorl of four to 24 seed cotyledons, or seed leaves. The seed leaves aid the growing seedling by drawing on the reserves of the seed. Next, single green or blue-green juvenile leaves appear, arranged spirally on the shoot. The seedling produces these leaves for six months to five years. Pine trees have small brown scale leaves that are also arranged spirally; these do not conduct photosynthesis. The mature leaves are green needles arranged in clusters that last from one and a half to four years.
Most pines have both male and female cones on one tree. In a few species, one sex or the other dominates. The male cones--1/2 inch to 2 inches long--usually appear in the spring, although some appear in the fall. They drop after shedding their pollen. The larger female cones--1 1/4 inch to 24 inches long--take one and a half to three years to mature. Fertile scales, each containing two small, winged seeds, are arranged spirally on the female cone. The scales at the base and tip of the cone do not have seeds.
A mature cone usually opens to release seeds that are blown by the wind. Cones that rely on birds to disperse the seeds have to be broken open by birds. Some pines, including the bishop pine and Canary Island pine, are called fire climax pines. They keep their seeds for years waiting for a forest fire to kill the parent tree--the heat bursts the mature cones, scattering the seeds to repopulate the burnt ground.
Pine Tree Adaptations
Pine trees are native to the temperate areas of Eurasia, but some have made special climate adaptations. Bristle cones, mountain pine, Siberian dwarf pine and the white bark pine grow well at high elevations and northern latitudes. Gray, pinyon and Turkish pines thrive in semi-arid climates.
Pine wood is softwood. It is useful for framing, floors, roofing and paneling, but not for outside use because it rots easily and attracts insects.