The class Pinopsida is characterized by generally small, always simple leaves and by the active secondary growth of stem and root. Many members of this group flourished from Lower Carboniferous times to the Permian age. Plants of the order Pinales (conifers) occur in the Northern Hemisphere; a few species occur within the tropics at sea level. Conifers are the most numerous of living gymnosperms and form large and relatively pure forests. Common examples of conifers are the pines, firs, spruces, redwoods, cedars, junipers, hemlocks, and larches. The wood of conifers is used extensively for construction of all kinds. It has no vessels and thus differs from the wood of angiosperm trees. Although conifers are called softwoods and angiosperm trees hardwoods, the wood of some pines is much harder than that of some angiosperms. Most conifers are monoecious, i.e., the male and female cones occur on the same tree. The microspores, or pollen grains, are produced in such vast abundance that clouds of pollen, carried on the wind, have settled on ships far at sea. In plants of the order Taxales (yews) the seeds, produced individually on short shoots, are surrounded by a conspicuous, fleshy covering.
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