Spruce

A spruce is a tree of the genus Picea, a genus of some 37 species of coniferous trees in the pine family, Pinaceae, found in the northern temperate and boreal (taiga) regions of the Northern Hemisphere. Picea is treated either in the subfamily Pinoideae, or the sole genus in its own subfamily Piceoideae.

Spruces can be distinguished from other genera of the family Pinaceae by their needles (leaves), which are four-sided and attached singly to small persistent peg-like structures (pulvini) on the twigs. The needles are shed when 4–10 years old, leaving the twigs rough with the retained pegs. Pests of spruce forestry include green spruce aphid, eastern spruce budworm, European spruce bark beetle, and great spruce bark beetle.

Spruce is a major producer of timber for construction, and of pulp for paper. It is the standard material for the soundboards of stringed instruments like acoustic guitars. Native Americans use the roots of some species for weaving baskets. The Norway spruce is widely used for Christmas trees. Artists including Augustin Hirschvogel in the 16th century, Edvard Munch around 1900, and Eija-Liisa Ahtila in the 21st century have depicted spruces in etchings, oil paintings, and video installations.

Etymology The scientific name derives from Latin "pix", pitch, which was obtained from the resin of Picea abies. Spruce, from Middle English or appears originally to have denoted goods, including wooden objects, imported from Prussia. The Middle English word is in turn from Old French , "Prussia".

Description Spruces differ from other Pinaceae in two distinctive characters. Firstly, they have a pulvinus (plural, pulvini), a small peg-like structure at the base of each needle, that remains when the needle falls. Secondly, they have evergreen needle-like leaves that are more or less square in cross-section. The needles stay on the tree for between four and ten years.

The tree usually has a straight trunk, though can become bushy or irregular if damaged by wind exposure or biotic factors like browsing or insect damage. Spruces are resinous, and monoecious, with separate male and female cones on the same tree. Young trees have a conical crown; in older trees, this tends to become a roughly cylindrical column; mature heights vary from 10–20 m in the smaller species like Picea mariana, up to a maximum of 100 m in Picea sitchensis. Branches grow from the trunk in regular whorls; the lower branches are mostly soon lost, except when the tree is open-grown in full sun. Young branches rise above the horizontal, but older branches do not. The needles range from 0.6–0.8 cm in Picea orientalis up to 3.5–5 cm in Picea smithiana. The cones have leaflike bracts that appear at the time of pollination, but unlike Abies (fir cones), these are generally later covered by the seed scales. When mature, the cones range from 2–3.5 cm in Picea mariana, up to 10–20 cm in Picea abies, and nearly as long but stouter and heavier, in Picea smithiana. Each seed sits with its lower half in a cup on the seed scale; the seeds have a large wing.

The structure of the cone scales, including length, width, immature colour, shape of the apex, and how much of the scale is free, is the most useful feature for identifying species of spruce.Douglas, G.W. (1975). Spruce (Picea) hybridization in west-central British Columbia. B.C. Min. For., Forest Science, Smithers B. C., unpublished report, cited by Coates, K. D.; Haeussler, S.; Lindeburgh, S.; Pojar, R.; Stock, A. J. (1994). "Ecology and silviculture of interior spruce in British Columbia". Canada/British Columbia Partnership Agreement For. Resour. Devel., Victoria, British Columbia, FRDA Rep. 220. 182 p. (Cited in Coates et al. 1994). While Picea glauca and Picea engelmannii, for example, differ in shoot and needle characteristics, those with cones present are most easily identified.Horton, K.W. (1956). A taxonomic and ecological study of Picea glauca and Picea engelmannii in North America. Diploma thesis, Oxford University.Horton, K.W. (1959). Characteristics of subalpine spruce in Alberta. Canadian Department of Northern Affairs and National Resources, Forestry Branch, Forest Resources Division, Ottawa, Ontario, Technical Note 76.Coupé, R.; Ray, C. A.; Comeau, A.; Ketcheson, M. V.; Annas, R. M. (1982). A guide to some common plants of the Skeena area, British Columbia. B. C. Mining and Forestry, Resources Branch, Victoria, British Columbia.

Spruces are generally of moderate lifespan, ranging from 100 to 600 years; the oldest reported age for a single tree is 852 years for a specimen of Picea engelmannii. Clonal reproduction can extend this; a Norway spruce P. abies clonal group in Dalarna, Sweden, nicknamed "Old Tjikko" has reproduced by layering, reaching a claimed age of 9,550 years for the clone as a whole, though not for the small trees that are part of it.

Evolution

Fossil history

The Picea lineage begins in the fossil record around 130 million years ago (mya). The oldest record of spruce that has been found in the fossil record is from the Early Cretaceous (Valanginian) of western Canada, around 136 million years old.

The only surviving branch of the lineage, however, diverged only around 30 mya, meaning that the rest of the crown group has no living descendants. That, in turn, means that the biogeography and ecology of the crown group cannot be inferred from living members of the genus. For example, middle Eocene spruce fossils have been found in the Buchanan Lake Formation of Canada (46.2–40.4 mya).

External phylogeny

Based on a transcriptome analysis, Picea is most closely related to the genus Cathaya; those form a clade, sister to the genus Pinus. These genera, with douglas-firs and larches, form the pinoid clade of the Pinaceae.

Another study produced broadly similar results, but with Cathaya sister to [Picea + Pinus]:

Internal phylogeny

DNA analyses have often conflicted with traditional classifications based on the morphology of needle and cone, but also conflict markedly between studies, with more proposed phylogenies than there are studies, and no consensus by 2015 on the relationships within the genus. In particular there is major discordance between phylogenies based on mitochondrial DNA (mtDNA) and those based on chloroplast DNA (cpDNA), and there is strong evidence for a history of reticulate evolution involving extensive hybrid introgression in the genus, which is continuing between several species, such as between Picea abies and Picea obovata (Picea × fennica), and between Picea glauca and Picea engelmannii (Picea × albertiana).

One of the earliest genetic studies used chloroplast DNA (cpDNA) to infer that P. breweriana is sister to all other Picea species, with P. sitchensis sister to those remaining species. However, subsequent studies have shown very different results, with both nuclear DNA and mtDNA placing P. sitchensis in a small clade with what had always been presumed from morphology to be its close relatives, P. glauca and P. engelmannii, with the cpDNA result anomalous; likewise, while P. breweriana has still been recovered as sister to all other species by some studies, it was recovered as deeply embedded in the genus by a study using a large set of nuclear, cp, and mtDNA. A further problem with several studies before 2013 was a combination of misidentified samples and contaminated DNA.

Taxonomy Taxonomic history In 1824, Albert Dietrich set up the genus Picea. In 1887, the German botanist Heinrich Moritz Willkomm revised the genus using vegetative characteristics of the trees, rather than of the cones. His classification was followed in 1890 by that of the German botanist Heinrich Mayr, and again in 1982 by that of the Taiwanese biologist Leroy Liu on a similar basis. In 1989 Peter A. Schmidt classified the species in the genus using mainly seed cone characteristics.

Species , Plants of the World Online accepted 37 species. As no consensus has emerged on relationships from genetic studies, they are listed below in alphabetical order:

Picea abies – Norway spruce, Europe; important in forestry, the original Christmas tree Picea alcoquiana – (syn. P. bicolor) Alcock's spruce, central Japan (mountains) Picea asperata – dragon spruce, western China; several varieties Picea aurantiaca Mast. (doubtfully distinct from P. asperata) Picea austropanlanica Silba (doubtfully distinct from P. purpurea) Picea brachytyla – Sargent's spruce, southwest China Picea breweriana – Brewer's spruce, Klamath Mountains, North America; local endemic Picea chihuahuana – Chihuahua spruce, northwest Mexico (rare, endangered) Picea crassifolia – Qinghai spruce, China Picea engelmannii – Engelmann spruce, western North American mountains; important in forestry Picea farreri – Burmese spruce, northeast Burma, southwest China (Yunnan) Picea glauca (syn. P. laxa) – white spruce, northern North America; important in forestry Picea glehnii – Glehn's spruce, northern Japan, Sakhalin Picea jezoensis – Jezo spruce, northeast Asia and Kamchatka south to Japan Picea koraiensis – Korean spruce, Korea, northeast China Picea koyamae – Koyama's spruce, Japan (mountains) Picea likiangensis – Likiang spruce, southwest China Picea linzhiensis (W.C.Cheng & L.K.Fu) Rushforth (syn. P. likiangensis var. linzhiensis) – Linzhi spruce, southeast Tibet (Yarlung Tsangpo valley) Picea mariana – black spruce, northern North America Picea martinezii – Martinez spruce, northeast Mexico (very rare, endangered) Picea maximowiczii – Maximowicz spruce, Japan (rare, mountains) Picea meyeri – Meyer's spruce, northern China (from Inner Mongolia to Gansu) Picea morrisonicola – Taiwan spruce, Taiwan (high mountains) Picea neoveitchii – Veitch's spruce, northwest China (rare, critically endangered) Picea obovata – Siberian spruce, north Scandinavia, Siberia; sometimes treated as a subspecies of P. abies (and hybridises with it), but has distinct cones Picea omorika – Serbian spruce, Serbia and Bosnia; local endemic; important in horticulture Picea orientalis – Caucasian spruce or Oriental spruce, Caucasus, northeast Turkey Picea polita (syn. P. torano) – tiger-tail spruce, Japan Picea pungens – blue spruce or Colorado spruce, Rocky Mountains, North America; important in horticulture Picea purpurea – purple cone spruce, western China Picea retroflexa – green dragon spruce, China Picea rubens – red spruce, northeastern North America; important in forestry Picea schrenkiana – Schrenk's spruce, mountains of central Asia Picea sitchensis – Sitka spruce, Pacific coast of North America; the largest species, to 95 m tall; important in forestry Picea smithiana – morinda spruce, western Himalaya, eastern Afghanistan, northern and northwest India Picea spinulosa – Sikkim spruce, northeast India (Sikkim) and Bhutan, eastern Himalaya Picea wilsonii – Wilson's spruce, western China

Natural hybrids These hybrids are known to occur naturally: Picea × albertiana S.Br. (P. engelmannii × P. glauca) Picea × fennica (Regel) Kom. (P. abies × P. obovata) Picea × lutzii Little (P. glauca × P. sitchensis) Picea × notha Rehder (Picea glehnii × Picea jezoensis)

Cultivated hybrids The following cultivated origin hybrids have been named; many others have been reported without being named: Picea × mariorika Boom (P. mariana × P. omorika) Picea × moseri Mast. (P. jezoensis × P. mariana) Picea × saaghyi Gayer (P. glauca × P. jezoensis) The un-named hybrid between Picea omorika and Picea sitchensis shows marked hybrid vigour and has been considered of potential interest in forestry.

Genome

The nuclear, mitochondrial and chloroplast genomes of British Columbia interior spruce Picea × albertiana have been sequenced. The large (20 Gbp) nuclear genome and associated gene annotations of interior spruce (genotype PG29) were published in 2013 and 2015.

Ecology

Establishment