No more than 35 species of spruce trees (Picea spp.) grow on Earth, all native to forests in the cool temperate regions of Asia, Europe and North America. According to The Gymnosperm Database, spruces are the closest relatives to pines (Pinus spp.), even though they don't closely resemble each other on many key features. Spruces make architecturally interesting specimen trees for gardens and are effective windbreaks.
Spruce trees develop with a single upright stem tip called a "leader" that eventually elevates them into tall hardwood trees of heights 50 to nearly 200 feet tall. Their habit is conical or spirelike with wide bases; some are very thin and narrow, while others are plump and rounded. They always taper at their tops.
The oldest and longest branches occur at the base of spruce trees. On the tree trunk, the branches radiate outward in all directions in a whorl. On each branch, new growth branchlets also occur in a whorl. Occasionally, weak, smaller twigs will appear off of the main branch not associated with the whorled branchlets that occur at the growth tip. Denuded sections of the branches feel rough to the touch because of persistent leaf bases.
Spruce foliage, often called needles, are short and stiff and radiate outward in all directions on the twigs and branches. Close inspection reveals that each needle is four-sided or three-sided. The needles are usually three-fourths inch to one inch long. Each needle attaches singularly to the twig upon a tiny woody base. Depending on species of tree, the needles persist as long as 10 years although excessive shading, drought or fire can cause premature needle loss.
Spruce trees do not flower but produce differently gendered cones, or clusters of woody scales. Female cones occur in late spring on the year-old parts of branches in the uppermost reaches of the tree. They are oval or oblong cylinders that are first held erect and colored light green with purplish tints. The male cones also appear on year-old branches, alone or in clusters in the crotches at the ends of branches toward the tree top. They are yellow to purplish red and shed pollen that is carried by the wind to the nearby female cones. Once fertilized, female cones become pendent and ripen to purple or brown when mature four to eight months later. The cone scales dry and release winged seeds that are dropped and moved by breezes to soil nearby. By the end of winter many mature female cones have shattered or broken away from the tree or will do so shortly.
Spruce trees, like pines, produce profuse amounts of pollen. The Pollen Library states that they are rarely considered particularly allergenic. An individual spruce pollen grain measures as large as 160 micrometers and has a bladder or sac that readily captures the wind for mobility.