Evolution And Classification
The oldest known fossil of the pine family (Pinaceae) is a cone from the Lower Cretaceous period, about 130 million years ago. The structure of this fossilized pine cone is similar to that of modern cones of the Pinus genus.
Today, there are about 100 species of pines. Pines grow throughout the Northern Hemisphere, and only one species (Pinus merkusii) is native to the Southern Hemisphere. More than 70 species are native to Mexico and Central America, and this is their likely center of origin. Pines are distributed in North America from the subarctic of northern Canada and Alaska to the tropics. There are about 35 species of pines in the United States and Canada. Although only one species is native to the Southern Hemisphere, many pines have been introduced and cultivated there for timber or as ornamental plants.
There are two subgenera of pines, and botanists believe these are evolutionarily distinct groups. These sub-genera are Diploxylon, commonly called the hard pines, and Haploxylon, commonly called the soft pines. As suggested by their names, the wood of soft pines tends to be soft, and the wood of hard pines tends to be hard.
The needles of hard pines have the following characteristics: (a) they usually arise in fascicles (bundles) of two or three; (b) they have a semicircular shape in cross-section; and (c) they have two main veins, as revealed by a cross-section. In addition, the fascicle sheaths of hard pines remain attached as the needles mature.
The needles of soft pines have the following characteristics: (a) they usually arise in fascicles (bundles) of five; (b) they have a triangular shape in cross-section; and (c) they have only one main vein, as revealed by a cross-section. In addition, the fascicle sheaths of soft pines wither away as the needles mature.
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