The blue spruce (Picea pungens), also commonly known as Colorado spruce or Colorado blue spruce, is a species of spruce tree native to North America in Arizona, Colorado, Idaho, New Mexico, Utah and Wyoming. It is noted for its often strongly glaucous blue-green needles, and has therefore been used as an ornamental tree in many places far beyond its native range.
Description
In the wild, Picea pungens grows to as much as in height, but more typically tall. When planted in parks and gardens it most often grows tall with a spread of . It has scaly gray-brown bark with a slight amount of a cinnamon-red undertone on its trunk, not as rough as an Engelmann spruce. On older trees the trunk bark becomes deeply furrowed and scaly. The trunk diameter may reach as much as . The root system is of the blue spruce is dense and compact, lacking a taproot.
Blue spruce is a conifer with a conical crown when young, but more open and irregular in shape as it becomes older. The stout branches grow out horizontally in well defined whorls, but lower branches droop downwards as trees age. Young twigs never hang downwards and are yellow-brown in color.
The narrow, needle-like, evergreen leaves are quite sharply pointed and may be dull green, blue, or pale white. The white or blue glaucous color is caused by surface waxes on the needles and is most visible on newly emerging foliage and fades towards summer. In the wild stands of trees tend to have similar coloration. Each of the needles is four sided with stomata on every side, stiff, and long. The needles are attached radially to their shoots, but curve upward. The leaf buds are golden brown and cone shaped. The buds may be in size and the tip may either be blunt or pointed.
The pollen producing cones, more properly strobili, develop throughout the crown of blue spruce trees, but are more common in the upper half of the crown. Pollen cones are mainly yellow with a touch of red and average long. The seed cones begin growing in May or June and release their mature seeds in the autumn of the same year in which they start to grow. When young they are purple-brown in color. When fully mature they are light brown, longer than they are wide, circular in cross section with thin, papery scales and can be curved or straight. The cones can measure between long, but are more typically . The seed cones are only found in the top tenth to quarter of the tree and are normally near the end of side branches.
The seeds are dark brown. They average 4 mm in length with the papery wing extending beyond the tip almost twice this length.
The blue spruce can be confused with four other spruce species, Engelmann spruce, European spruce (Picea abies), white spruce (Picea glauca), and black spruce Picea mariana), however only the range of the Engelmann spruce overlaps with the blue spruce in the wild. Though larger for the blue spruce, the measurements of their cones and cone scales overlap with the Engelmann spruce. The cones of the Engelmann measuring 3–8 cm with the scales measuring 3–8 mm beyond the seed impression while the blue spruce measures 5–12 cm with scales that measure 8–10 mm beyond the seed impression. However, the twigs of the Engelman are always finely hairy while those of the blue are usually hairless.
Chemistry The phytochemistry of the blue spruce is relatively little studied. The ripe seeds have a 1.17% yield of essential oils while the cones produce only 0.38% when steam distilled for four hours. The main component, over 40%, of the essential oils is limonene with β-Pinene and α-Pinene the next most significant.
Taxonomy
Picea pungens was given its first valid scientific description by George Engelmann in 1879. He had previously named it Abies menziesii in 1862 and later as Picea menziesii in 1863, but both those names had already been used making them illegitimate names. The specimens of the tree used to describe it were collected by Charles Christopher Parry on Pikes Peak, also in 1862.
There was confusion regarding the correct scientific name for the species during the late 1800s and early 1900s with Picea parryana believed by many to be the correct name, though with various authorities attached to it. This was caused by the 1876 description of it as a variety of Abies menziesii named parryana by André Michaux coming before its description by Engelmann in 1879. Despite this, Picea pungens was used as the correct name throughout this time by well known scientists such as Ludwig Beissner, Alfred Rehder, and Augustine Henry. By 1925 Picea pungens was being used for the species in US government scientific publications. It is classified in the genus Picea as part of the family Pinaceae. It has no accepted varieties, but has several in its heterotypic synonyms.
Table of Synonyms Name Year Rank Notes Abies commutata var. glauca 1889 variety Abies menziesii 1862 species nom. illeg. Abies menziesii var. parryana 1876 variety Abies parlatorei 1923 species Picea commutata 1891 species Picea menziesii 1863 species nom. illeg. Picea menziesii var. parryana 1876 variety Picea parryana 1905 species Picea parryana argentea 1887 Picea parryana glauca-pendens 1898 Picea parryana glauca-pendula 1901 Picea pungens f. argentea 1918 form nom. illeg. Picea pungens f. argentea 1887 form Picea pungens argentea-pendula 1899 nom. subnud. Picea pungens f. coerulea 1891 form Picea pungens var. compacta 1916 variety Picea pungens f. compacta 1915 form Picea pungens var. glauca 1883 variety Picea pungens f. glauca 1887 form Picea pungens glauca-pendens 1897 Picea pungens f. glauca-pendula 1891 form Picea pungens var. hunnewelliana 1923 variety Picea pungens f. hunnewelliana 1949 form Picea pungens var. kosteriana 1912 variety Picea pungens f. kosteriana 1939 form Picea pungens f. pendens 1949 form Picea pungens var. pendula 1907 variety Picea pungens subvar. pendula 1898 subvariety Picea pungens f. pendula 1920 form nom. illeg. Picea pungens f. perpendicularis 1920 form Picea pungens f. typica 1920 form not validly publ. Picea pungens var. viridis 1883 variety Picea pungens f. viridis 1939 form Pinus armata 1907 species Pinus parryana 1907 species nom. illeg.
Genetic analysis of the genus Picea indicates that the closest living relative of the blue spruce may be Picea mexicana, a disputed species from northern Mexico also known as Picea engelmannii subsp. mexicana. Together they are part of a group with seven other related species that includes all the species from North America except for Brewer's spruce (Picea breweriana). The related species include Sitka spruce (Picea sitchensis), white spruce (Picea glauca) and Engelmann spruce (Picea engelmannii), black spruce (Picea mariana), red spruce (Picea rubens), Chihuahua spruce (Picea chihuahuana), and Nuevo León spruce (Picea martinezii). Though visually very similar, the blue spruce and Engelmann spruce split from their common ancestor between 10 and 20 million years ago.
Names Picea, the genus name, is thought to come from the Latin word pix meaning "pitch", a reference to the typical sticky resin in spruce bark. The specific epithet pungens means "sharply pointed", referring to the leaves.
The most frequently used common name in English is blue spruce. It was first used for other trees in 1817 and is still used for any spruce tree with a glaucous blue color to their needles, but most frequently meaning Picea pungens. Though this is the most common name, in the wild only part of the population has the waxy blue-gray coating for which the tree is named. Less frequently, but still common, is Colorado blue spruce, a name first used in 1912. The usage of Colorado spruce dates to 1881, but is less frequent than the longer alternate. Due to its affinity with streams and well watered canyons it is also known as the water spruce. Occasionally encountered are the names Parry's spruce, prickly spruce, silver spruce, and white spruce. Blue spruces are also rarely called silvertip fir, but this name is also applied to Abies magnifica especially when sold as Christmas trees. In addition it is sometimes labeled as Colorado green spruce or green spruce by plant nurseries or tree farms.
Similar to the meaning of the scientific name, the Navajo name for this species is a compound c'ó deniní with c'ó meaning spruce and deniní meaning "it is sharp".
Ecology
Blue Spruce occurs at high elevations, in the forests of the South Central Rockies and in the Southern Rocky Mountains. It grows in mesic montane conifer forests, often associating with Rocky Mountain Douglas-fir, ponderosa pine, or white fir. It has a riparian affinity, preferring moist soils such as those along streams or at the edges of wet meadows. The Douglas-fir or ponderosa pine only become associated with streams at lower, warmer elevations. It also may be found alongside the quaking aspen (Populus tremuloides) in the high mountain habitats of desert ranges in the Intermountain West. At the lowest elevations of its range it also becomes associated with aspens in the well watered stream bottoms with their deep alluvial soils. Though associated with the Rocky Mountain Douglas-fir, the blue spruce is more tolerant of drought and intense sunlight.
Blue spruce usually grows in cool and humid climatic zones where the annual precipitation mainly occurs in the summer. Blue spruce is generally considered to grow best with abundant moisture. Nevertheless, this species can withstand drought better than any other spruce. It can withstand extremely low temperatures (-40 degrees C) as well. Furthermore, this species is more resistant to frost damage compared to other associated species.
Distributed soil types and topography Blue spruce generally exists on gentle uplands and sub irrigated slopes, in well-watered tributary drainage, extending down intermittent streams, and on lower northerly slopes.
Blue spruce is considered as a pioneer tree species in moist soil in Utah.
Rooting habits Blue spruce seedlings have shallow roots that penetrate approximately into the soil during the first year of growth. Although freezing can't damage much in blue spruce, frost heaving will cause seedling loss. Shadows in late spring and early autumn minimize this frost heaving loss. Despite the shallow roots, blue spruce is able to resist strong winds.
Pests and diseases The blue spruce is attacked by two species of Adelges, an aphid-like insect that causes galls to form. Nymphs of the pineapple gall adelgid form galls at the base of twigs which resemble miniature pineapples and those of the Cooley's spruce gall adelgid cause cone-shaped galls at the tips of branches. The larva of the spruce budworm eat the buds and growing shoots while the spruce needle miner hollows out the needles and makes them coalesce in a webbed mass. An elongated white scale insect, the pine needle scale feeds on the needles causing fluffy white patches on the twigs and aphids also suck sap from the needles and may cause them to fall and possibly dieback. Mites can also infest the blue spruce, especially in a dry summer, causing yellowing of the oldest needles. An occasional insect pest is the spruce beetle (Dendroctonus rufipennis) which bores under the bark. It is much more likely to use Engelmann spruces as the host trees and generally prefers to feed on trees that have been knocked over unless their numbers become very high.
The blue spruce is susceptible to several needle casting diseases which cause the needles to turn yellow, mottled or brown before they fall off. Various rust diseases also affect the tree causing yellowing of the needles as well as needle fall. Canker caused by Cytospora attacks one of the lower branches first and progressively makes its way higher up the tree. The first symptom is the needles turning reddish-brown and falling off. Meanwhile, patches of white resin appear on the bark and the branch eventually dies.