Coniferae

(also Pinidae), the most numerous and most widely distributed subclass of gymnospermous plants. The subclass includes trees and, less commonly, shrubs. The crown is often conical. Most species are evergreen, but some, for example, the larch, are deciduous in the winter. The wood consists of tra-cheids with bordered pits; xylem parenchyma is undeveloped or absent. The annual growth rings are usually pronounced. The bark and the wood have resin canals. The primary root is usually preserved for life, often developing into a massive taproot; the small lateral roots for the most part contain mycorrhiza. The leaves are usually entire, needlelike, and sessile; some are scale-like and lamellar (linear, lanceolate). The leaf structure is xero-morphic. In many conifers the leaves are in clusters on short shoots.

The strobiles are unisexual. The male strobiles consist of an axis upon which are arranged reduced microsporophylls bearing microsporangia. Microspores (pollen), many of which are equipped with air sacs, form in the microsporangia. The female, or car-pellate, strobiles are gathered into cones that consist of an axis, upon which lie covering scales with modified megastrobiles, or seed scales. On the upper side of the scales are one, two, or several ovules (megasporangia), which develop into the female gam-etophyte. The latter bears an archegonium with egg cells. Pollination is by wind. Conifers are for the most part monoecious. After fertilization, the embryo, surrounded by endosperm and having two to 15 cotyledons, develops. The seeds vary greatly in structure and shape. Vegetative reproduction is poorly developed.

Conifers, an ancient group of seed plants, first appeared in the Carboniferous period. Some families, for example, Lebachiaceae and Voltziaceae, are known only in fossil form. Extant conifers belong to eight families: Araucariaceae, Podocarpaceae, Cephal-otaxaceae, Taxaceae, Pinaceae, Sciadopityaceae, Taxodiaceae, and Cupressaceae. There are about 55 genera, embracing 600 species. The USSR has more than 50 species, not counting cultivated ones. Conifers include many very large trees, with some attaining heights of 50–60 m and even 100 m (Sequoia, Sequoiadendron) and diameters of 6–9 m. Some conifers have lifespans of several millennia. Conifers include some low shrubs and spreading forms. The New Caledonian species Podocarpus ustus parasitizes the roots of other conifers.

Many conifers play a primary role in the plant cover of the earth, covering extensive areas especially in Eurasia and North America. Conifers are extremely important in water conservation, landscaping, and national economies. They are major sources of lumber, pulp and paper, rosins, turpentine, and tannins. The seeds of some conifers, including dwarf stone pines, Italian stone pines, and Araucaria, are used as food; their oil is also used. Many conifers are valuable ornamentals.