Spruce

Many species of spruce will interbreed with each other, sometimes forming populations of hybrids that are fertile and have characteristics intermediate to those of the parents. When hybridization occurs in a genus, it is difficult for taxonomists to decide the exact number of species that are present. As a result, it is estimated that there are 35-40 species of spruces, depending on which taxonomic treatment is adopted. There are also a number of well-defined hybrids between some of the true species.

Seven species of spruces occur in North America, and some additional species have been widely planted in forestry or horticulture. The richness of native spruce species is greatest in China, where 18 species occur.

The most widespread species of spruce in North America is white spruce (Picea glauca), which ranges through almost all of boreal and temperate Canada and the northeastern United States. Black spruce (P. mariana) has a somewhat less extensive, more northern distribution, and it tends to occur in wetter sites than white spruce, including bogs. Red spruce (P. rubens) occurs in eastern Canada and New England and at high altitudes in the Appalachians.

The other spruces of North America are western in distribution. Engelmann spruce (P. engelmannii) is a widespread, montane species in the Rocky Mountains. Blue spruce (P. pungens) occurs in the southern Rocky Mountains. Sitka spruce (P. sitchensis) is widespread in humid forests of the west coast, ranging from southern Alaska to central California. Brewer spruce (P. breweriana) has a very restricted distribution in southern Oregon.

The Norway spruce (P. abies) is the most widespread species in western and central Europe. This species occurs naturally in that region, and it has also been cultivated as an economic species for at least three centuries. Norway spruce has also been introduced to North America for use in forestry and for planting in parks and around homes.