A group of evergreen trees found in most of the cool temperate regions of the northern hemisphere, of pyramidal form, especially in a young state, with branches in tiers. Leaves linear or needle-like, mostly four-sided, arranged spirally on the shoots, but the undermost ones usually twisted at the base, so as to crowd them more on the upper side of the twig than on the lower. Each leaf is seated on a slight cushion which, if the leaf be gently pulled off downwards whilst fresh, it brings mostly away. When, however, the leaf falls naturally, or the twig is dried for herbarium purposes, it leaves at the base a peg-like stump. These leaf-stumps thickly studded on the shoot are extremely characteristic of the spruces, and well distinguish them from the firs (Abies). Flowers unisexual, both sexes produced on the same tree at or near the end of the twigs; the males solitary, stalked, composed of numerous anthers. Female cones nearly always pendulous, their scales persisting until they fall. Seeds winged.
Some botanists divide Picea into three sections, but in Pilger’s view a subdivision into two sections only is more natural. These are:
sect. picea (sect. Eupicea Willk.; sect. Cassicta Mayr, pro max. part.) – Leaves with four faces and four angles, rhombic in cross-section, with rows of stomata on all four surfaces. In some species the stomata are more numerous on the downward-facing (ventral) surface. To this section belong all the species except those listed below.
sect. omorika – Leaves flattened, with stomata usually on the ventral surface only, so that there is a marked contrast between the green, exposed surface and the bluish or whitish inner or downward-facing surface. The species belonging to this section are: P. omorika (the only European member); P. breweriana and P. sitchensis (N. America); and the Asiatic P. spinulosa, P. brachytyla, and P. jezoensis.
In the last century, the spruces were almost always called “Abies” in Britain, whilst the true silver-firs (Abies) were called “Picea”. This inversion of names dates from Loudon’s time and should be borne in mind when consulting his great work. But it has its source in Linnaeus’ Species Plantarum (1753), in which he named the common spruce Pinus abies and the European silver fir Pinus picea. This incidentally explains how it has come about that the common spruce is correctly called Picea abies (L.) Karsten. The name of the European silver fir would be Abies picea (L.) Bluff & Fingerhut (1825) were it not that Philip Miller used that name earlier for the common spruce (in his Dictionary, ed. 1768).
The confusion over the names Abies and Picea is now a thing of the past, but the following distinctions between the two genera may still be useful:
Picea (Spruces) – Leaves inserted on peg-like stumps (see first paragraph); mostly they are rhombic in cross-section and, if flat, then the lines of stomata are concentrated on the ventral side, i.e., that which is morphologically the upper side of the leaf, since it faces towards the apex of the shoot. But the appressing or forward leaning of the leaves on the upper side of a horizontal shoot exposes the green back (dorsal side) of the leaf without the need for any twisting at the base; the same is also true of a vertical leading shoot, where the primary leaves are closely appressed. Further, in Picea the cones are pendent, with persistent scales, and fall in one piece.
Abies (Silver firs) – Leaves nearly always flat, not falling away in drying, nor leaving the peg-like stumps of Picea. In marked contrast to that genus, the stomata are concentrated on the dorsal side of the leaf, i.e., on the morphologically lower side of the leaf (facing towards the base of the shoot), which is the normal arrangement in flowering plants. Consequently, an appressed leaf in Abies would expose its white underside but for the fact that the base of the leaf is twisted through about 18o°, as can be seen by examining the upper central leaves on a shoot of, say, Abies nordmanniana. In Abies the cones are erect, and break up on the tree, i.e., the scales fall away from the central axis, which remains on the branch.
The spruces have scarcely the garden value of the firs, but the following are handsome and effective: P. brachytyla, P. breweriana, P. jezoensis var. hondoensis, P. likiangensis, P. omorika, P. orientalis, P. polita, P. pungens (silver and glaucous forms), P. smithiana, and P. spinulosa.
The species of Picea should always be raised from seed if this is available. The dwarf garden varieties are propagated by cuttings taken in July or August. Grafting is used to increase varieties abnormal in habit and those with coloured leaves, notably the various blue and silver forms of P. pungens; some species have to be propagated in this way, if seed is not available or scarce, but such plants are not so fine or long-lived as those raised from seed. The spruces like abundant moisture at the root; if rainfall is deficient it may be compensated for by planting in a deep moist soil. P. pungens is one of the best in a dry climate. Few conifers withstand town conditions worse than the spruces, and they are not really at home on shallow, chalky soils. Many of them produce a useful timber, especially P. abies in Europe. P. glauca is cultivated in some of the northerly regions of Scandinavia too inclement for any other tree to thrive.
The measurements of cultivated trees, as throughout this revised edition, have been provided by Mr A. F. Mitchell of the Forestry Commission. Much fuller information will be found in his recently published work Conifers in the British Isles (Forestry Commission Booklet 33, publ. 1972). This contains descriptions of all coniferous species cultivated in the British Isles, and keys based on field characters.
From the Supplement (Vol. V)
Horsman, John – ‘Spruces in Cultivation’, The Plantsman, Vol. 5(2), pp. 103-27 (1983).
Liu, Tang-shu – ‘A New Proposal for the Classification of the Genus Picea’, Acta Phytotax. Geobot., Vol. 33, pp. 227-45 (1982).
Liu, Tang-shu – ‘Spruces in the Arnold Arboretum’, Arnoldia, Vol. 42, pp. 102-29(1982).
Schmidt-Vogt, H. – Die Fichte, Vol. 1, (1977). Although mainly devoted to P. abies, this work contains an excellent survey of the genus as a whole (pp. 9-163).