Among coniferous trees the pines constitute by far the most important group, regarded either from the point of view of number of species or that of economic value. As timber trees they easily predominate over any other genus in the northern hemisphere. They are evergreen, and range from trees over 200 ft high to mere shrubs; very resinous, producing their branches in tiers.
The leaves of pines are nearly always produced in clusters or bundles of from two to five, occasionally there are six, and in P. cembroides monophylla they are solitary. Each bundle is really a much reduced lateral spur, which bears at the base a few scale-like bracts (the sheath), followed by leaves in the number characteristic of the species, after which the growing point of the spur aborts. The seedling leaves of all pines are solitary, the adult condition commencing to appear in the second and third years. The individual leaf or ‘needle’ is long and narrow, mostly finely toothed at the margin, and always more or less conspicuously lined with rows of minute white, or whitish, dots called stomata. Where the leaves are in bundles of two the transverse section of each is semicircular, in the bundles of three to five they are three-sided. Each bundle of leaves, whatever their number, forms in the aggregate a slender cylinder. At the base of each bundle is a sheath, whose varying length and duration give very useful indications of the identity of the species. The leaf-bearing shoots of each season are always to a greater or less extent naked at the base, being furnished there with ‘scale-leaves’ only – small, thin, membranous bodies, often fringed, and usually falling away quickly. The terminal winter-bud is an important differentiating character according to its shape and size, the character of the scales by which it is covered, and whether it be resinous or not, although in some species the last character is variable.
The flowers of pines are unisexual and borne in conical clusters, the males at the base, the females at the apex of the year’s growth; the female inflorescence develops the second year into a woody fruit often of great size and weight, commonly known as a cone, and of egg-shaped, cylindrical, or tapered form. These cones are composed of a number of woody scales which vary in length, in thickness, and in the character of the scar or boss at the end, and in the presence or absence of spines. When the cone is ripe (most frequently at the end of the second year), the scale opens and allows the two seeds at its base to escape; but some species take longer, and several appear never to release their seeds at all unless through some outside agency such as fire (in the West American forests), or squirrels, or birds. Some species have small seeds which are furnished with a large membranous wing whose object is to assist in their dispersion. The larger, edible seeds have only rudimentary wings or none at all.
As garden or park trees the pines are of varying merit, but the best of them are amongst the noblest of evergreens. They do not need a rich soil so much as an open, well-drained one. The hardier ones, like P. banksiana, P. uncinata and P. sylvestris, grow in some of the most inclement parts of the globe. On chalky soils P. nigra, P. brutia, P. halepensis, P. pinea and others succeed very well. For spots exposed to sea-gales and in maritime situations generally P. nigra, P. radiata, P. muricata, P. pinaster, and P. thunbergii are extremely useful in building up the first line of protection against sea-winds. The genus has given rise to many valuable dwarf varieties, suitable for the rockgarden or as specimens in small gardens, and some species are naturally dwarf, e.g., P. pumila and P. mugo.
The garden varieties have to be increased by grafting on the types to which they belong, but all other pines must be grown from seed. With few exceptions it is desirable to get them planted in their permanent places as young as possible.
From the Supplement (Vol. V)
Farjon, Aljos – Pines. Leyden, 1984. A descriptive work illustrated throughout by the author’s own excellent drawings, showing the habit of the tree, cones and foliage, and with distribution maps.
Horsman, John – ‘Pines in Cultivation’, The Plantsman, Vol. 2(4), pp. 225-6 (1981).