Coniferæ. This important and interesting order of dicotyledons attained its maximum importance during past geological periods; its world-wide geographical distribution and strongly marked family and generic differences being in this way explained—i.e. when we regard the existing forms as the survivors of a larger and once predominant coniferous flora, which has been in good part displaced by the more recent and higher monocotyledonous and dicotyledonous (angiospermous) forms. About 300 species, included in about 33 genera, now remain. Leaving the questions of floral morphology and minute structure which separate the conifers (along with Cycads and Gnetaceæ) from the remaining phanerogams or 'angiosperms' to the article GYMNOSPERMS, it may be most profitable here to make a rapid survey of the most important groups of the order, with their principal types. Various systems of classification have been propounded; an old and widely adopted one recognises three sub-orders, the pines (Abietineæ), cypresses (Cupressineæ), and yews (Taxineæ). Since, however, the first two of these are much less widely separated from each other than from the third, later systematists are returning to the classification of Lindley, and regard these as making up a single sub-order (Pinoideæ) equivalent to the yew (Taxoideæ). On account of the exceptional importance of this order, alike in forestry and horticulture, a brief enumeration of the families of these sub-orders, with mention of their most important species, may now be given.
Commencing with the Abietineæ division of Pinoideæ, we find three families, the pines proper (Abietineæ), Araucarias (Araucariineæ), and Taxodiums (Taxodiineæ). The genus Abies (including Picea) consists of evergreen trees, or sometimes shrubs, in which the linear and always more or less completely needle-shaped leaves arise singly, and are never clustered in branchlets, while the scales of the cones are not thickened at the tip. The list may be headed by the Spruce Fir, or Norway Spruce (A. excelsa), one of our commonest trees, while A. Douglasii, A. nobilis, and other Californian species are of special beauty as trees and value as timber, with other species too numerous to mention. The old Linnean genus Pinus (from which the firs, larches, and cedars have been separated off as Abies, Larix, and Cedrus respectively) still includes about 100 species, easily distinguished from Abies by the grouping of the leaves upon arrested branchlets, the thickening of the tips of the cone-scales, and other characters. Among the more important species, P. sylvestris (the Scotch fir), P. austriaca (the Austrian pine), P. Laricio (the Corsican pine), P. Pinaster (the cluster pine), and P. Pinea (the stone pine of southern Europe), may be first mentioned, alike on account of their frequency of occurrence in forests and plantations in Europe, and as agreeing in having usually only two leaves on each branchlet. A large and chiefly Californian series agrees in having three leaves on each sheath. Of these, P. insignis (the Oregon pitch pine), P. Benthamiana, and P. radiata may be mentioned; finally a series, usually five-leaved, includes the Weymouth Pine and White Pine of North-east America (P. Strobus), the Siberian Stone Pine (P. Cembra), &c. Of the allied genus Larix (see LARCH) only L. europæa (decidua) need here be mentioned, while of Cedrus (see CEDAR) C. Libanus and C. Deodara are of special importance. The Araucariineæ are familiarly represented by the A. imbricata of Chili, so common in suburban gardens (see ARAUCARIA), and other more graceful but usually less hardy species; as also by the important Kauri pine and other species of Dammara. See DAMMAR.
The Taxodiineæ include a number of very important trees, notably the curious umbrella pine (Sciadopitys) of Japan, Cunninghamia sinensis of China, and the colossal Sequoia (Wellingtonia gigantea) of California, with its allied species (see SEQUOIA). In addition to these we may mention also the Japanese Cedar (Cryptomeria japonica, the Virginian Bald Cypress (Taxodium distichum).
Among the Cupressineæ we have first the cypresses proper, which includes besides the well-known genus Cupressus (see CYPRESS) the closely allied Retinospora of Japan. Juniperus (see JUNIPER) alone forms another sub-family; while Thuja (see ARBOR VITÆ) with its immediate allies Thuja, Juniperus and Libocedrus constitute a third; and Callitris with Actinostrobus and Fitzroya make up the fourth.
Passing now to the sub-order of yews (Taxoideæ) we have again two main divisions, the yews proper or Taxeæ, and the Podocarpeæ. Among the latter we shall only mention the oriental genus Podocarpus, and the beautiful Dacrydium cupressinum of New Zealand; but the former are of much greater variety and importance (see YEW). Besides the species of Taxus, we have especially the Chinese and Japanese Cephalotaxus, the curious Ginkgo (Salisburia) adiantifolia of the same region, together with the Chinese and Californian species of Torreya.
In addition to the general article GYMNOSPERMS, and to those devoted to particular genera or species of conifers, the reader should especially consult Engler's Pflanzenfamilien, both for a full summary of our present knowledge and copious references. For the purposes of the English horticulturist Veitch's Manual of Coniferæ is most exhaustive, while Gordon's Pinctum, and Hemsley's Handbook of Hardy Trees, &c. (Lond. 1877), will be found of service to the amateur.