White Spruce

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iWhite Spruce

Scientific classification

Kingdom:	Plantae
Division:	Pinophyta
Class:	Pinopsida
Order:	Pinales
Family:	Pinaceae
Genus:	Picea
Species:	P. glauca

Binomial name

Picea glauca
(Moench) Voss

The White Spruce (Picea glauca) is a medium-sized evergreen tree growing to 15-30 m tall, rarely to 40 m tall, and with a trunk diameter of up to 1 m. It is native to the north of North America, from central Alaska east to Newfoundland, and south to northern Montana, Michigan and Maine; there is also an isolated population in the Black Hills of South Dakota and Wyoming.

Foliage and cones

The bark is thin and scaly, flaking off in small circular plates 5-10 cm across. The crown is narrow conic in young trees, becoming cylindric in older trees. The shoots are pale buff-brown, glabrous (hairless) in the east of the range, but often pubescent in the west, and with prominent pulvini. The leaves are needle-like, 12-20 mm long, rhombic in cross-section, glaucous blue-green above with several thin lines of stomata, and blue-white below with two broad bands of stomata.

The cones are pendulous, slender cylindrical, 3-7 cm long and 1.5 cm broad when closed, opening to 2.5 cm broad. They have thin, flexible scales 15 mm long, with a smoothly rounded margin. They are green or reddish, maturing pale brown 4-6 months after pollination. The seeds are black, 2-3 mm long, with a slender, 5-8 mm long pale brown wing.

Varieties

Several geographical varieties have been described, but are not accepted as distinct by all authors. These comprise, from east to west:

Picea glauca var. glauca (Typical or Eastern White Spruce). From Newfoundland east to eastern Alberta, on lowland plains.
Picea glauca var. densata (Black Hills White Spruce). The Black Hills.
Picea glauca var. albertiana (Alberta White Spruce). The Rocky Mountains in Alberta, British Columbia and northwest Montana.
Picea glauca var. porsildii (Alaska White Spruce). Alaska and Yukon.

The two western varieties are distinguished by pubescent (downy) shoots, and may be related to extensive hybridisation and/or intergradation with the closely related Engelmann Spruce found further south in the Rocky Mountains. White Spruce also hybridises readily with the closely related Sitka Spruce where they meet in southern Alaska; this hybrid is known as Picea × lutzii.

White Spruce is the northernmost tree species in North America, reaching just north of 69°N latitude in the Mackenzie River delta (Arno & Hammerly 1984).

White Spruce is the Provincial tree of Manitoba and the State tree of South Dakota.

[edit] Uses

Dwarf Alberta Spruce with reverted foliage

White Spruce is of major economic importance in Canada for its wood, harvested for paper-making. It is also used to a small extent as a Christmas tree.

A dwarf cultivar of the Alberta White Spruce, Picea glauca var. albertiana 'Conica', is a very popular garden plant. It has very slender leaves, like those normally found only on one-year-old White Spruce seedlings, and very slow growth, typically only 2-10 cm per year. Older specimens commonly 'revert', developing normal adult foliage and starting to grow much faster; this 'reverted' growth must be pruned out if the plant is to be kept dwarf.