Picea glauca

White spruce, or *Picea glauca*, is a medium-sized evergreen conifer found across the northern temperate and boreal forests of North America. Its range stretches from west-central Alaska eastward through much of Canada—including western, southern, central, and eastern regions—all the way to the Avalon Peninsula in Newfoundland. In the United States, it grows south into Montana, North Dakota, Minnesota, Wisconsin, Michigan, upstate New York, and Vermont, as well as the mountainous and immediate coastal parts of New Hampshire and Maine, where conditions are just cool and moist enough. An isolated population also exists in the Black Hills of South Dakota and Wyoming. Besides white spruce, it goes by names like Canadian spruce, skunk spruce, cat spruce, and—depending on the variety—Black Hills spruce, western white spruce, Alberta white spruce, or Porsild spruce.

This tree typically reaches 15 to 30 meters (50 to 100 feet) tall, with a trunk up to 1 meter (3.3 feet) in diameter. Reports of much greater heights—40 to 50 meters—actually refer to a taller, separate hybrid now called *Picea × albertiana*. The bark is thin and scaly, flaking off in small circular plates 5 to 10 centimeters across. Young trees have a narrow conical crown that becomes columnar with a conical top as they age. Shoots are pale buff-brown and smooth in the eastern part of the range but often hairy in the west, with prominent raised leaf bases. The needle-like leaves are mostly 8 to 13 millimeters long (occasionally up to 20 or even 25 millimeters), rhombic in cross-section, and glaucous blue-green on top (hence the name *glauca*), with several thin lines of stomata, and blue-white underneath with two broad bands of stomata.

The cones hang down and are slender and cylindrical, 2.5 to 7 centimeters long and about 1.5 centimeters wide when closed, opening to 2.5 centimeters wide. Their scales are thin and flexible, about 15 millimeters long, with smoothly rounded edges. Cones start green or reddish and turn pale brown 4 to 8 months after pollination. The seeds are black, 2 to 3 millimeters long, with a slender, tan wing 5 to 8 millimeters long.

Seeds are small—2.5 to 5 millimeters long—oblong, and pointed at the base. The number of sound seeds per cone ranges from 32 to 130 on average. Empty seeds often result from lack of pollination, ovule abortion, or insect damage. Each seed weighs between 1.1 and 3.2 milligrams and is clasped by a thin wing two to four times its length. The seed and wing lie flat against the cone scale. Initially, the embryo and megagametophyte are soft and translucent; later, the endosperm becomes firm and milky white, while the embryo turns cream or light yellow. At maturity, the seed coat darkens rapidly from light brown to dark brown or black. Mature seeds snap cleanly in two when cut with a sharp knife on a firm surface.

Cones reach their maximum size after about 800 growing degree days. Their moisture content drops gradually after roughly 1000 growing degree days. Cone color—which can be red, pink, or green when immature—helps gauge maturity. How and when cones are collected and stored affects germination and early seedling growth. One imperial bushel (about 36 liters) of cones—roughly 6,500 to 8,000 cones—yields 6 to 20 ounces (170 to 570 grams) of clean seed.

Seed dispersal begins after cone scales reflex, usually in late summer or early fall of the year the cones form. Cones open when their moisture content is between 45% and 70% and their specific gravity is 0.6 to 0.8. Weather influences both when and how seeds are released, but opening and dispersal patterns can differ among trees in the same stand. Cold, damp weather causes cone scales to close again; they reopen in dry conditions. Most seeds fall early, but dispersal can continue through fall, winter, and even into the next growing season. Seeds are initially carried by wind. While small amounts normally travel beyond 100 meters from the source, seeds have been found more than 300 to 400 meters away.

The root system is highly adaptable, responding to soil moisture, fertility, and compaction. On shallow or restrictive soils, roots form a plate-like structure, but this is not a fixed genetic trait—under better conditions, white spruce develops several long, running roots just below the surface. The structure of tracheids in the long lateral roots changes with soil nitrogen availability.

White spruce can live for several hundred years, with an average lifespan of 250 to 300 years. Slow-growing trees in harsh climates can be especially long-lived; for example, trees only 6 to 10 meters tall on the shore of Urquhart Lake in the Northwest Territories were found to be over 300 years old.

Mature bark is scaly or flaky, gray-brown or ash-brown, and looks silvery when freshly exposed. Resin blisters are usually absent, though the Porsild spruce variety (*Picea glauca var. porsildii*) is said to have smooth, resin-blistered bark. Bark thickness is generally less than 8 millimeters and never more than 9.5 millimeters.

The compound isorhapontin can be found in white spruce. The species has three distinct genomes: a nuclear genome, a mitochondrial genome, and a chloroplast genome.