The Blue Spruce or Colorado Spruce (Picea pungens) is a medium-sized evergreen tree growing to 25-30 m tall, exceptionally to 46 m tall, and with a trunk diameter of up to 1.5 m. It is native to western North America, from southeast Idaho and southwest Wyoming, south through Utah and Colorado to Arizona and New Mexico. It grows at high altitudes from 1800-3000 m altitude, though unlike Engelmann Spruce in the same area, it does not reach the alpine tree-line. It is most commonly found growing along streamsides in mountain valleys, where moisture levels in the soil are greater than the often low rainfall in the area would suggest.

The bark is thin and scaly, flaking off in small circular plates 5-10 cm across. The crown is conic in young trees, becoming cylindric in older trees. The shoots are stout, orange-brown, usually glabrous, and with prominent pulvini. The leaves are needle-like, 15-30 mm long, stout, rhombic in cross-section, dull gray-green to bright glaucous blue (very variable from tree to tree in wild populations), with several lines of stomata; the tip is viciously sharp.

The cones are pendulous, slender cylindrical, 6-11 cm long and 2 cm broad when closed, opening to 4 cm broad. They have thin, flexible scales 20-24 mm long, with a wavy margin. They are reddish to violet, maturing pale brown 5-7 months after pollination. The seeds are black, 3-4 mm long, with a slender, 10-13 mm long pale brown wing.

Blue Spruce does not normally hybridise with other spruces, though hybrids with Engelmann Spruce have been found very rarely.

Uses

Blue Spruce is one of the most popular garden conifers, grown for its strongly glaucous foliage. Numerous cultivars selected for particularly bright blue foliage have been selected by the horticultural trade, some of them also slow-growing dwarf forms suitable for planting in small gardens. It is also sometimes used as a christmas tree, though the very sharp needles make it a poor choice for families with children.

Blue Spruce is the State Tree of Colorado (where it is commonly known as Colorado Spruce) and Utah.

External links

• Gymnosperm Database
• Flora of North America
• Arboretum de Villardebelle - photos of cones of Picea pungens and related spruces