Trees or shrubs, generally resinous, and for the greater part evergreen. Wood destitute of medullary rays; that is to say, a transverse section does not show the lines from the centre to the circumference so conspicuous especially in the young wood of most exogenous plants. Leaves alternate, opposite, or fascicled in a membranous sheath, often narrow, needle-like and rigid, or reduced to dense imbricating scales, rarely with a flattened limb. Flowers monoecious or dioecious, destitute of perianth : males in catkins, sometimes conoid, with one stamen or several, and then monadelphous; females in cones or solitary, when in cones two or more at the base of each bract. By some authors these are considered as naked seeds on an open carpellary leaf, and by others as inverted or erect carpels, each containing a solitary erect seed destitute of the usual integuments or coats. For the purposes of this work it matters little which view we adopt, but we shall follow the usual course and refer to them as ovules and seeds. The seed is albuminous, with usually more than two cotyledons, and sometimes as many as 12 in two opposite fascicles. The genera are variously estimated according to the views of different systematists, but they are reduced to about 30 by the more moderate. The species - which are widely dispersed, occurring in most temperate countries, and rare in the tropic and arctic regions - number between 200 and 300. The number of species and varieties in cultivation belonging to this order is very great, though many of them are still very rare, and others are too tender for our climate. We shall confine ourselves to descriptions of the most desirable hardy species.

The genera may be conveniently grouped in three tribes, founded upon the nature of the fruit.