Picea engelmannii, with the common names Engelmann spruce, white spruce, mountain spruce, and silver spruce, is a species of spruce native to western North America. It is mostly a high-altitude mountain tree but also appears in watered canyons. Description Picea engelmannii is a medium-sized to large evergreen tree growing to tall, exceptionally to tall, and with a trunk diameter of up to . The reddish bark is thin and scaly, flaking off in small circular plates across. The crown is narrow conic in young trees, becoming cylindric in older trees. The shoots are buff-brown to orange-brown, usually densely pubescent, and with prominent pulvini. The leaves are needle-like, long, flexible, 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 needles have a pungent odour when crushed. Purple cones of about 1 cm appear in spring, releasing yellow pollen when windy. The cones are pendulous, slender cylindrical, 2.5–8 cm long and 1.5 cm broad when closed, opening to 3 cm broad. They have thin, flexible scales 15–20 mm long, with a wavy margin. They are reddish to dark purple, maturing to light brown 4–7 months after pollination. The seeds are black, 2–3 mm long, with a slender, 5–8 mm long light brown wing. The tree grows in a krummholz form along the fringe of alpine tundras. Distribution Engelmann spruce is native to western North America, primarily in the Rocky Mountains and east slopes of the Cascade range from central British Columbia to Southern Oregon in the Cascades and commonly in Montana, Idaho, and Colorado, and more sparsely towards Arizona and New Mexico in the Sky islands; there are also two isolated populations in Northern Mexico. It is mostly a high-altitude mountain tree, in many areas reaching the tree line, but at lower elevations occupies cool watered canyons. It grows from above sea level, rarely lower towards the northwest. It appears in the canyons of the Idaho Panhandle and more limitedly in the northeastern Olympic Mountains; the latter includes exceptionally large specimens, e.g. one thick and tall. It can be found in the Cascade Range (mostly on the eastern slopes) from elevations of and liberally in the Rocky Mountains. It can also be found in the Monashee and Selkirk Mountains, as well as the highlands surrounding the Interior Plateau. Ecology Both water uptake and water stored in roots appear to