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Picea glauca
(Moench) Voss
White Spruce
Pinaceae
Picea glauca is a coniferous tree species in the family Pinaceae. It is widespread across much of Alaska, Canada, and the northern United States, and is commonly cultivated. It is the provincial tree of Manitoba, and a form of the species is the state tree of South Dakota (FNAEC 1993).
Description
Picea glauca is a medium to tall tree, growing up to 40 m tall with a trunk that grows up to 1 m in diameter, forming a narrowly conical crown. Branches are horizontal to ascending, with horizontal or sometimes drooping branchlets. Needles are stiff, straight or curved slightly forward, around 1.5 to 2 cm long, square in cross section, with a pointed tip. They are generally grayish to bluish green with two to four whitish bands (which are stomata) on all sides of the needles. As with other species in the genus Picea, the needles are attached to the twig via a woody "peg" that persists after the needle has fallen. Buds are around 4 to 6 mm long, and are not resinous. The bark is reddish gray and flaky. Twigs are yellowish to reddish brown and are usually hairless. Pollen cones are 1 to 2 cm, red. Seed cones are around 3 to 6 cm long, hanging down from the branchlets. They are green, ripening to brown. The cone scales are thin, round, woody, stiff and brittle in texture. Seeds are 2 to 4 mm long, with a wing that is 5 to 8 mm long (Eckenwalder 2009).
Picea glauca can be distinguished from the similar red spruce (Picea rubens) and black spruce (Picea mariana) by its cones, which are somewhat longer than those two species, and its twigs, which are usually hairless (Picea rubens and P. mariana have hairy twigs). Additionally, Picea rubens does not have a bluish-gray cast to its needles (i.e. they are not glaucous). In the west, it is similar to the Engelmann spruce (Picea engelmannii), but the cone scales of that species are relatively pointed and irregularly toothed at the tip, while Picea glauca has cone scales that are rounded and untoothed at the tip (Eckenwalder 2009).
Several varieties of Picea glauca have been named, but the status of them is unclear. Variety porsildii has smooth bark with resin blisters, variety albertiana has shorter cones and longer, more spreading pegs (called “sterigmata”, plural of sterigma). Variety densata corresponds to the isolated population in the Black Hills of Wyoming and South Dakota, and has a denser growth habit (Strong and Hills 2006; MBG). These are variously treated as varieties of Picea glauca, or hybrids of Picea engelmannii, in which case they fall under the name Picea × albertiana (Strong and Hills 2006; Eckenwalder 2009). Variety densata is sometimes considered to be a cultivar, in which case it would be called ‘Densata’ (MBG).
Picea glauca can be distinguished from the similar red spruce (Picea rubens) and black spruce (Picea mariana) by its cones, which are somewhat longer than those two species, and its twigs, which are usually hairless (Picea rubens and P. mariana have hairy twigs). Additionally, Picea rubens does not have a bluish-gray cast to its needles (i.e. they are not glaucous). In the west, it is similar to the Engelmann spruce (Picea engelmannii), but the cone scales of that species are relatively pointed and irregularly toothed at the tip, while Picea glauca has cone scales that are rounded and untoothed at the tip (Eckenwalder 2009).
Several varieties of Picea glauca have been named, but the status of them is unclear. Variety porsildii has smooth bark with resin blisters, variety albertiana has shorter cones and longer, more spreading pegs (called “sterigmata”, plural of sterigma). Variety densata corresponds to the isolated population in the Black Hills of Wyoming and South Dakota, and has a denser growth habit (Strong and Hills 2006; MBG). These are variously treated as varieties of Picea glauca, or hybrids of Picea engelmannii, in which case they fall under the name Picea × albertiana (Strong and Hills 2006; Eckenwalder 2009). Variety densata is sometimes considered to be a cultivar, in which case it would be called ‘Densata’ (MBG).
Uses
Note: Please see the disclaimer regarding any information about medical or edible uses.
Picea glauca is an important timber tree and is the major source of timber in the boreal forest; it is used for carpentry, flooring, general construction, musical instruments, and especially pulpwood (Farjon 2013). It is often cultivated as an ornamental. For example, the variety or cultivar densata prefers moist, well-drained soils, full sun, and cold winter climates, and grows in USDA zones 3 to 6 (MBG). The cultivar ‘Conica’ is a dwarf conifer with a neat, compact growth form belonging to the albertiana taxon, and is very popular (Farjon 2013; RHS).
Distribution
Picea glauca is a major component of the boreal forest, and forms pure stands or can be associated with paper birch (Betula papyrifera) and other conifers and hardwoods. It grows at altitudes of up to 2100 m above sea level (Farjon 2013). It is the most widespread spruce in North America (Farjon 2013); it is native to all Canadian provinces and territories, and in the United States it is native to Alaska, Montana, Minnesota, Wisconsin, Michigan, New York, New Hampshire, Vermont, and Maine, with scattered populations in Idaho, Wyoming and South Dakota (Kartesz 2015; Eckenwalder 2009). Populations have also been introduced in Massachusetts, Connecticut, Rhode Island, Pennsylvania, New Jersey, and Kentucky (Kartesz 2015).
Status
Picea glauca, including its varieties, is listed on the IUCN Red List as “Least Concern”, as its range is extremely wide, covering much of Canada, and there are no significant threats to the species (Farjon 2013).
References
Eckenwalder, J. E. 2009. Conifers of the world: the complete reference. Portland: Timber Press.
Farjon, A. 2013. Picea glauca. The IUCN Red List of Threatened Species. https://dx.doi.org/10.2305/IUCN.UK.2013-1.RLTS.T42323A2972485.en.
FNAEC (Flora of North America Editorial Committee), editor. 1993. Flora of North America, north of Mexico. Volume 2: Pteridophytes and Gymnosperms. New York: Oxford University Press.
Kartesz, J. T., The Biota of North America Program (BONAP). 2015. North American Plant Atlas. (http://bonap.net/napa). Chapel Hill, N.C. [maps generated from Kartesz, J.T. 2015. Floristic Synthesis of North America, Version 1.0. Biota of North America Program (BONAP). (in press)].
MBG (Missouri Botanical Garden), Picea glauca ‘Densata’. Plant Finder. [accessed 2022 Aug 6]. http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=c224
RHS (Royal Horticultural Society). Picea glauca ‘Conica’. RHS Gardening. [accessed 2022 Aug 6]. https://www.rhs.org.uk/plants/83270/picea-glauca-var-albertiana-conica/details
Strong, W. L., and Hills, L. V. 2006. Taxonomy and origin of present-day morphometric variation in Picea glauca (× engelmannii) seed-cone scales in North America. Canadian Journal of Botany, 84: 1129–1141.
Farjon, A. 2013. Picea glauca. The IUCN Red List of Threatened Species. https://dx.doi.org/10.2305/IUCN.UK.2013-1.RLTS.T42323A2972485.en.
FNAEC (Flora of North America Editorial Committee), editor. 1993. Flora of North America, north of Mexico. Volume 2: Pteridophytes and Gymnosperms. New York: Oxford University Press.
Kartesz, J. T., The Biota of North America Program (BONAP). 2015. North American Plant Atlas. (http://bonap.net/napa). Chapel Hill, N.C. [maps generated from Kartesz, J.T. 2015. Floristic Synthesis of North America, Version 1.0. Biota of North America Program (BONAP). (in press)].
MBG (Missouri Botanical Garden), Picea glauca ‘Densata’. Plant Finder. [accessed 2022 Aug 6]. http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=c224
RHS (Royal Horticultural Society). Picea glauca ‘Conica’. RHS Gardening. [accessed 2022 Aug 6]. https://www.rhs.org.uk/plants/83270/picea-glauca-var-albertiana-conica/details
Strong, W. L., and Hills, L. V. 2006. Taxonomy and origin of present-day morphometric variation in Picea glauca (× engelmannii) seed-cone scales in North America. Canadian Journal of Botany, 84: 1129–1141.
Description
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