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Blue spruce

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Blue spruce

Secure  (NatureServe)[2]
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Gymnospermae
Division: Pinophyta
Class: Pinopsida
Order: Pinales
Family: Pinaceae
Genus: Picea
Species:
P. pungens
Binomial name
Picea pungens
Engelm., 1879
Synonyms[3]
  • Abies menziesii Engelm. (1862)
  • Abies parlatorei Dallim. & A.B.Jacks. (1923)
  • Picea commutata Beissn. (1891)
  • Picea menziesii Engelm. (1863)
  • Picea parryana (André) Sarg. (1905)
  • Pinus armata Voss (1907)
  • Pinus parryana (André) Voss (1907)

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.[4] It is noted for its blue-green colored needles, and has therefore been used as an ornamental tree in many places far beyond its native range.[5]

Description

[edit]

In the wild, Picea pungens grows to as much as 50 meters (164 ft) in height,[6] but more typically 30 m (98 ft) tall.[7] When planted in parks and gardens it most often grows 9 to 18 m (30 to 60 ft) tall with a spread of 3 to 6 m (10 to 20 ft).[8] It has scaly grey-brown bark with a slight amount of a cinnamon-red undertone on its trunk, not as rough as an Engelmann spruce.[7] On older trees the trunk bark will be deeply furrowed and scaly.[9] The diameter of the trunk may reach as much as 1.5 m (4.9 ft).[6]

Blue spruces are conifers with a pyramidal or conical crown when young, but more open and irregular in shape as they become older.[7] The stout branches grow out horizontally in well defined whorls,[7] but lower branches droop downwards as trees age.[10] Young twigs are never hang downwards and are yellow-brown in color.[6]

The narrow, needle like, evergreen leaves are quite sharply pointed and may be dull green, blue, or pale white.[9] Each of the needles is four sided with stomata on every side, stiff, and 1.6–3 centimeters (3⁄4–1+1⁄4 in) long.[6] The needles are attached radially to their shoots, but curve upward. The leaf buds are golden brown and cone shaped.[11] The buds may be 6 to 12 millimeters (1⁄4 to 1⁄2 in) in size and the tip may either be blunt or pointed.[6]

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.[12] Pollen cones are mainly yellow with a touch of red and average 1.5 cm (1⁄2 in) long.[7] 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.[13] When young they are purple-brown in color.[7] When fully mature they are light brown with thin, papery scales and are often curved. Overall they are longer than they are wide, between 8 and 15 cm (3 and 6 in) long, and circular in cross section.[13][14] The seed cones are only found at the top of the tree. This helps to facilitate cross-pollination.[15]

The seeds are dark brown.[11] They average 4 mm in length with the papery wing extending beyond the tip almost twice this length.[7]

Taxonomy

[edit]

Picea pungens was given its first valid scientific description by George Engelmann in 1879. He had previously named it Abies menziesii in 1862 and then as Picea menziesii in 1863 after, but both those names had already been used making them illegitimate names.[3]

Names

[edit]

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.[8] The specific epithet pungens means "sharply pointed", referring to the leaves.[16]

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.[17] 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.[7] 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.[18][19] Occasionally encountered are the names Parry's spruce, prickly spruce, silver spruce, and white spruce.[9] Blue spruces are also rarely called silvertip fir,[20] but this name is also applied to Abies magnifica especially when sold as Christmas trees.[21] In addition it is sometimes labeled as "Colorado green spruce" or "green spruce" by plant nurseries or tree farms.[22][23]

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".[24]

Ecology

[edit]

Blue Spruce occurs at high elevations, 1,830 to 2,740 meters (6,000 to 8,990 ft) in the forests of the South Central Rockies and 2,130 to 3,050 meters (6,990 to 10,010 ft) in the Southern Rocky Mountains.[12] It grows in mesic montane conifer forests, often associating with Douglas-fir, ponderosa pine, or white fir. It has a riparian affinity.[5]

Climate

[edit]

Blue spruce usually grows in cool and humid climatic zones where the annual precipitation mainly occurs in the summer.[25]

Blue spruce is most common in Colorado and the Southwest. The annual average temperature ranges from 3.9 to 6.1 degrees C (39 to 43 degrees F). And ranges from - 3.9 to - 2.8 degrees C (25 to 27 degrees F) in January. In July, the average temperature ranges from 13.9 to 15.0 degrees C (57 to 59 degrees F). The average minimum temperature in January ranges from - 11.1 to 8.9 degrees C (12 to 16 degrees F), and the average maximum temperature in July ranges from 21.1 to 22.2 C (70 to 72 degrees F). There is a frost-free period of about 55 to 60 days from June to August.[26][27]

Annual mean precipitation generally vary from 460 to 610 mm (18 to 24 in). Winter is the season with the poorest rainfall, the precipitation is usually less than 20 percent of the annual moisture falling from December to March. Fifty percent[dubious – discuss] of the annual precipitation occurs during the growing season of the plants.[26][28]

Blue spruce is generally considered to grow best with abundant moisture. Nevertheless, this species can withstand drought better than any other spruce.[29] It can withstand extremely low temperatures (-40 degrees C) as well. Furthermore, this species is more resistant to high insolation and frost damage compared to other associated species.[25]

Distributed soil types and topography

[edit]

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.[30]

Blue spruce always grow naturally in the soils which are in the order Mollisols, and the soil will also be in the orders histosols and inceptisols in a lesser extent.[30][31][32]

Blue spruce is considered as a pioneer tree species in moist soil in Utah.[33]

Rooting habits

[edit]

Blue spruce seedlings have shallow roots that penetrate aproximately 6 centimeters (2.5 in) into the soil during the first year of growth.[34] 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.[35][36] Despite the shallow roots, blue spruce is able to resist strong winds.[37] Five years before transplanting, the total root surface area of 2-meter-high trees was doubled by pruning the roots of blue spruce. It also increases the root concentration in drip irrigation pipeline from 40% to 60%, which is an advantage in landscape greening.[38]

Pests and diseases

[edit]

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.[39][40] Another insect pest is the spruce beetle (Dendroctonus rufipennis) which bores under the bark. It often first attacks trees which have blown over by the wind and when the larvae mature two years afterwards, a major outbreak occurs and vast numbers of beetles attack nearby standing trees.[41]

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.[39]

It is also relatively intolerant of light populution and when planted near street lights or other outdoor lighting its preparation for winter can be delayed and parts of the tree may be damaged.[42]

Range

[edit]

The native range of the blue spruce is largely in the Central and Southern Rocky Mountains and moist mountain valleys and canyons to the west.[13][7] In New Mexico it only grows naturally in the higher mountain ranges of the state such as the Sandia–Manzano Mountains, Sangre de Cristo Mountains, and San Juan Mountains, as well as on Sierra Blanca Peak to the south.[43][44] In Arizona the range is even more limited, growing in just Coconio and Apache counties.[45] In Apache County it is found in the White Mountains in central eastern Arizona and the Lukachukai Mountains in the northeastern corner of the state. In Coconino County they only grow on the Kaibab Plateau.[44] The blue spruce grows in every county in the western two-thirds of Colorado;[46] approximately half of natural range of the species is in the Mountain of Colorado.[47] In Utah they are a locally common part of forests in the Uinta Mountains. West of the Uintas blue spruces are less frequent in canyons south of Salt Lake City.[31]

The blue spruce has become naturalized outside of its native range. In North America has escaped from cultivation in the states of Minnesota and New York. It has also become established to some extent in many western and northern European countries including Iceland, Norway, Sweden, the United Kingdom, France, and Belgium. In middle and southern Europe it is found in Germany, Switzerland, Austria, the former Czechoslovakia, and mainland Italy. To the east it grows in European portions of Russia, the Caucasus, and Bulgaria.[3]

Notable trees

[edit]

The tallest known blue spruce tree is an individual in the San Juan Mountains of southern Colorado in the Hermosa Creek area. When measured by Matt Markworth in 2015 it was 54.9 meters (180 ft) tall.[5]

Cultivation

[edit]
'Mission Blue' blue spruce new growth in spring

Picea pungens and its many cultivars are often grown as ornamental trees in gardens and parks.[13][5] It is also grown for the Christmas tree industry.[12] It grows best in USDA growing zones 1 through 7,[48] though it also does well in zones warmer than 7 where summer heat is moderate, as at San Francisco.[49]

Common cultivars (those marked agm have gained the Royal Horticultural Society's Award of Garden Merit):[50]

  • 'Baby Blue Eyes', 'Baby Blueeyes', or 'Baby Blue'[51] – This is a semi-dwarf cultivar that grows slowly, but may eventually reach 4.6–6.1 meters (15–20 ft) in height. It has a pyramidal shape and holds its color well.[52]
  • 'Fat Albert' – compact perfect cone to 3.0–4.6 meters (10–15 ft) of a silver blue color[53]
  • 'Globosa' agm[54] – shrub from 90–150 centimeters (3–5 ft) in height[55]
  • 'Hoopsii' agm[56] – A full size variety with a dense pyramidal habit known for "excellent" silver-blue color of its foliage. It reaches 9.1–15.2 meters (30–50 ft) tall when full grown.[57]
  • 'Koster' – A medium sized cultivar that will reach 8–10 meters (26–33 ft)[58]
  • 'Montgomery' – a slow growing dwarf variety. It will typically only grow 90–120 centimeters (3–4 ft) tall in eight years, but may eventually reach a height of over 2.4 meters (8 ft).[59]
  • 'Pendula' – drooping branches, spreads to about 1.2–3.0 meters (4–10 ft) wide by 0.6–1.8 meters (2–6 ft) tall[60]
  • 'Sester's Dwarf' – denser foliage than the species, slowly grows to about 1.8–2.4 meters (6–8 ft) tall[61]
Foliage of the cultivar 'Globosa'

Culture

[edit]

The Navajo and Keres Native Americans use this tree as a traditional medicinal plant and a ceremonial item, and twigs are given as gifts to bring good fortune. In traditional medicine, an infusion of the needles is used to treat colds and settle the stomach. This liquid is also used externally for rheumatic pains.[62]

The blue spruce is the state tree of Colorado.[63] It officially became Colorado's state tree on 7 March 1939 when House Joint Resolution 7 was enacted by the legislature. Previously a vote of the state's school children was taken on Arbor Day in 1892 expressing their preference for the blue spruce as the state tree.[64]

From 1933 until 2014 the blue spruce was also the state tree of Utah. It was replaced by the quaking aspen because the aspen is a great deal more common than the blue spruce in Utah, making up 10% of the state's tree cover.[65][66]

[edit]
  • Mature tree
    Mature tree
  • Mature cone
    Mature cone
  • Immature cone
    Immature cone
  • Hoopsii
    Hoopsii
  • Koster
    Koster
  • Globosa
    Globosa
  • Montgomery
    Montgomery
  • Fat Albert
    Fat Albert

See also

[edit]

References

[edit]
  1. ^ Farjon, A. (2013). "Picea pungens". IUCN Red List of Threatened Species. 2013: e.T42333A2973433. doi:10.2305/IUCN.UK.2013-1.RLTS.T42333A2973433.en. Retrieved 19 November 2021.
  2. ^ NatureServe (2024). "Picea pungens". Arlington, Virginia. Retrieved 7 September 2024.
  3. ^ a b c "Picea pungens Engelm". Plants of the World Online. Royal Botanic Gardens, Kew. Retrieved 24 September 2024.
  4. ^ Flora of North America Editorial Committee, editor. 1993. Flora of North America North of Mexico. Volume 2. Pteridiophytes and Gymnosperms. Oxford University Press, New York, 475 pp
  5. ^ a b c d Earle, Christopher J. (26 February 2023). "Picea pungens (blue spruce) description". The Gymnosperm Database. Archived from the original on 11 December 2023. Retrieved 24 September 2024.
  6. ^ a b c d e Taylor, onald J. (5 November 2020). "Picea pungens". Flora of North America. Retrieved 21 September 2024.
  7. ^ a b c d e f g h i Cronquist, Arthur; Holmgren, Arthur H.; Holmgren, Noel H.; Reveal, James L. (1972). Intermountain Flora. Vascular Plants of the Intermountain West, U.S.A.. Vol. 1, Geological and Botanical History of the Region. New York: New York Botanical Garden by Hafner Publishing Company. p. 224. OCLC 320442. Retrieved 21 September 2024.
  8. ^ a b "Picea pungens". Plant Finder. St. Louis, Missouri: Missouri Botanical Garden. Archived from the original on 23 May 2024. Retrieved 21 September 2024.
  9. ^ a b c Harrison, S.G.; Dallimore, William; Jackson, A. Bruce (1966). A Handbook of Coniferae and Ginkgoaceae (Forth ed.). London: Edward Arnold. p. 373. Retrieved 22 September 2024.
  10. ^ "Picea pungens (Blue Spruce, Colorado Spruce)". North Carolina Extension Gardener Plant Toolbox. North Carolina State University. Retrieved 22 September 2024.
  11. ^ a b Krüssmann, Gerd (1972). Handbuch der Nadelgehölze [Handbook of Conifers] (in German). Berlin: Paul Parey. pp. 216–217. ISBN 3-489-71422-9. OCLC 304738. Retrieved 23 September 2024.
  12. ^ a b c Burns, Russell M.; Honkala, Barbara H. (December 1990). "Picea pungens Engelm". Silvics of North America. Washington, D.C.: United States Forest Service. United States Department of Agriculture. ISBN 9780160271458. LCCN 91600537. OCLC 25008780. Archived from the original on 22 July 2024. Retrieved 24 September 2024.
  13. ^ a b c d Barnes, Burton V.; Wagner, Warren H. Jr. (1981) [1913]. Michigan Trees: A Guide to the Trees of Michigan and the Great Lakes Region. Illustrations by Sarah Phelps (Revised and Enlarged ed.). Ann Arbor, Michigan: University of Michigan Press. pp. 78–79. ISBN 978-0-472-08018-2. LCCN 80039717. OCLC 7170918. Retrieved 1 October 2024.
  14. ^ Vedel, H.; Lange, J. (1962). Trees and Bushes. Methuen & Co. pp. 119–120. ISBN 978-0416617801.
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  16. ^ Harrison, Lorraine (2012). RHS Latin for gardeners. United Kingdom: Mitchell Beazley. p. 224. ISBN 9781845337315.
  17. ^ "blue spruce". Oxford English Dictionary (Online ed.). Oxford University Press. doi:10.1093/OED/7006545120. (Subscription or participating institution membership required.)
  18. ^ Quattrocchi, Umberto (2012). CRC World Dictionary of Medicinal and Poisonous Plants. Boca Raton, Florida: CRC Press. p. 2923. ISBN 978-1-4822-5064-0. OCLC 774639599.
  19. ^ "Colorado spruce". Oxford English Dictionary (Online ed.). Oxford University Press. doi:10.1093/OED/1207804688. (Subscription or participating institution membership required.)
  20. ^ Heil, Kenneth D.; O'Kane, Jr., Steve L.; Reeves, Linda Mary; Clifford, Arnold (2013). Flora of the Four Corners Region: Vascular Plants of the San Juan River Drainage, Arizona, Colorado, New Mexico, and Utah (First ed.). St. Louis, Missouri: Missouri Botanical Garden. p. 89. ISBN 978-1-930723-84-9. ISSN 0161-1542. LCCN 2012949654. OCLC 859541992. Retrieved 6 October 2024.
  21. ^ Stuart, John David; Sawyer, John O. (2001). Trees and Shrubs of California. Illustrated by Andrea J. Pickart (First ed.). Berkeley, California: University of California Press. pp. 31–32. ISBN 978-0-520-22109-3. OCLC 44267780.
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  24. ^ Young, Robert W.; Morgan, William (1980). The Navajo Language : A Grammar and Colloquial Dictionary (in English and Navajo). Albuquerque, New Mexico: University of New Mexico Press. p. 296. ISBN 978-0-8263-0536-7. Retrieved 5 October 2024.
  25. ^ a b Fechner, Gilbert H. "Blue Spruce". Retrieved 2018-11-23.
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  27. ^ Pearson, G. A. "Forest types in the Southwest as determined by climate and soil". U.S. Department of Agriculture, Technical Bulletin 247: 144p.
  28. ^ Pearson, G. A. "Forest types in the Southwest as determined by climate and soil". U.S. Department of Agriculture, Technical Bulletin 247: 144p.
  29. ^ Goor, A. Y. (1977). "Forest tree planting in arid zones". Soil Science. 124 (1): 504p. Bibcode:1977SoilS.124...66C. doi:10.1097/00010694-197707000-00012.
  30. ^ a b Fechner, Gilbert H. "Blue Spruce". Retrieved 2018-11-22.
  31. ^ a b Mauk, Ronald L.; Henderson, Jan A. (1984). "Coniferous Forest Habitat Types of Northern Utah". USDA Forest Service General Technical Report (INT-170). Ogden, Utah: Intermountain Forest and Range Experiment Station: 31–32. Retrieved 9 October 2024.
  32. ^ Moir, William H.; Ludwig, John A. "A classification of spruce-fir mixed conifer habitat types of Arizona and New Mexico". USDA Forest Service, Research Paper RM-207.
  33. ^ Dixon, Helen (1935). "Ecological Studies on the High Plateaus of Utah". Botanical Gazette. 97 (2): 272–320. doi:10.1086/334554. JSTOR 2471603. S2CID 84538967.
  34. ^ Jones, John R. (1973). "Southwestern Mixed Conifers". Silvicultural systems for the Major Forest Types of the United States. Agriculture Handbook No. 445 (First ed.). Washington, D.C.: U.S. Department of Agriculture. p. 47. Retrieved 5 October 2024.
  35. ^ Alexander, Robert R. (1974). "Silviculture of central and southern Rocky Mountain forests : a summary of the status of our knowledge by timber types". USDA Forest Service Research Paper (RM-120). Fort Collins, Colorado: Rocky Mountain Forest and Range Experiment Station: 19. Retrieved 5 October 2024.
  36. ^ Pearson, G. A. "Forest types in the Southwest as determined by climate and soil". U.S. Department of Agriculture, Technical Bulletin 247.
  37. ^ Goor, A. Y.; Barney. Forest tree planting in and zones. Ronald Press.
  38. ^ Watson, Gary; Sydnor, T. Davis (1 May 1987). "The Effect of Root Pruning on the Root System of Nursery Trees". Arboriculture & Urban Forestry. 13 (5): 126–130. doi:10.48044/jauf.1987.027. Retrieved 5 October 2024.
  39. ^ a b Gilman, Edward F.; Watson, Dennis G. (2011-05-01). "Picea pungens: Colorado Spruce". EDIS. IFAS Extension Service: University of Florida. Retrieved 2013-10-06.
  40. ^ Cranshaw, W. S. (2013-06-13). "Scale Insects Affecting Conifers". Colorado State University Extension. Retrieved 2013-10-05.
  41. ^ Ciesla, Bill (2013-04-19). "Spruce Beetle Threatens High Country Spruce Forests". Colorado State University Extension. Retrieved 2013-10-05.
  42. ^ Sjöman, Henrik; Anderson, Arit (2023). The Essential Tree Selection Guide: For Climate Resilience, Carbon Storage, Species Diversity and Other Ecosystem Benefits (First ed.). Bath, England: Filbert Press. pp. 161–163. ISBN 978-1-7399039-4-7. OCLC 1400102923.
  43. ^ Wooton, Elmer Ottis; Standley, Paul Carpenter (1915). Flora of New Mexico. Contributions from the United States National Herbarium, Volume 19 (First ed.). Washington, D.C.: Smithsonian Institution. p. 34. LCCN agr15001072. OCLC 3786500. Retrieved 5 October 2024.
  44. ^ a b Little, Elbert L. (1950). Southwestern Trees : A Guide to the Native Species of New Mexico and Arizona (First ed.). Washington, D.C.: U.S. Department of Agriculture. pp. 17–18. Retrieved 5 October 2024.
  45. ^ Picea pungens, USDA Natural Resources Conservation Service PLANTS Profile, 5 October 2024
  46. ^ Ackerfield, Jennifer (2015). Lipscomb (ed.). Flora of Colorado (First ed.). Fort Worth, Texas: Botanical Research Institute of Texas. p. 61. ISBN 978-1-889878-45-4. OCLC 910162216.
  47. ^ Johnson, David W. (2014). "Picea pungens". In Stimm, Bernd; Roloff, Andreas; Lang, Ulla M.; Weisgerber, Horst (eds.). Enzyklopädie der Holzgewächse: Handbuch und Atlas der Dendrologie [Encyclopedia of Woody Plants: Handbook and Atlas of Dendrology] (in German). Weinheim, Germany: Wiley. pp. 1–8. doi:10.1002/9783527678518.ehg1996012. ISBN 978-3-527678518. OCLC 900416230.
  48. ^ "Colorado Blue Spruce". treecanada.ca. Retrieved 2018-11-20.
  49. ^ "Blue spruce (Picea pungens)". 11 February 2023.
  50. ^ "AGM Plants - Ornamental" (PDF). Royal Horticultural Society. July 2017. p. 78. Retrieved 25 April 2018.
  51. ^ "Baby Blue Colorado Spruce - Picea pungens 'Baby Blue Eyes'". WSU Clark County Extension – PNW Plants. Pullman, Washington: Washington State University. Archived from the original on 13 July 2024. Retrieved 24 September 2024.
  52. ^ "Picea pungens 'Baby Blueeyes'". Plant Finder. St. Louis, Missouri: Missouri Botanical Garden. Archived from the original on 24 September 2024. Retrieved 24 September 2024.
  53. ^ "Picea pungens 'Fat Albert'". Plant Finder. St. Louis, Missouri: Missouri Botanical Garden. Archived from the original on 28 February 2023. Retrieved 24 September 2024.
  54. ^ "Picea pungens (Glauca Group) 'Globosa' – Colorado spruce 'Globosa'". Conifers/RHS. London: Royal Horticultural Society. Archived from the original on 28 February 2024. Retrieved 24 September 2024.
  55. ^ "Picea pungens 'Glauca Globosa'". Plant Finder. St. Louis, Missouri: Missouri Botanical Garden. Archived from the original on 23 May 2024. Retrieved 24 September 2024.
  56. ^ "Picea pungens (Glauca Group) 'Hoopsii' – Colorado spruce 'Hoopsii'". Conifers/RHS. London: Royal Horticultural Society. Archived from the original on 8 December 2021. Retrieved 24 September 2024.
  57. ^ "Picea pungens 'Hoopsii'". Plant Finder. St. Louis, Missouri: Missouri Botanical Garden. Archived from the original on 3 July 2024. Retrieved 24 September 2024.
  58. ^ with a conical shape"Picea pungens (Glauca Group) 'Koster' – Colorado spruce 'Koster'". Conifers/RHS. London: Royal Horticultural Society. Archived from the original on 24 September 2024. Retrieved 24 September 2024.
  59. ^ "Picea pungens 'Montgomery'". Plant Finder. St. Louis, Missouri: Missouri Botanical Garden. Archived from the original on 21 September 2024. Retrieved 24 September 2024.
  60. ^ "Picea pungens 'Pendula'". North Carolina Extension Gardener Plant Toolbox. Raleigh, North Carolina: North Carolina State University. Archived from the original on 22 September 2024. Retrieved 24 September 2024.
  61. ^ "Sester's Dwarf Blue Spruce - Picea pungens 'Sester's Dwarf'". WSU Clark County Extension – PNW Plants. Pullman, Washington: Washington State University. Archived from the original on 7 July 2024. Retrieved 24 September 2024.
  62. ^ U. Michigan-Dearborn: Ethnobotany Accessed 2020-12-20
  63. ^ "State Trees & State Flowers". United States National Arboretum. June 11, 2009. Archived from the original on 2010-12-06. Retrieved 2010-05-26.
  64. ^ "Symbols & Emblems". Colorado State Archives. Government of Colorado. Archived from the original on 18 August 2024. Retrieved 25 September 2024.
  65. ^ Randle, Sterling (13 February 2014). "Quaking Aspen moves closer to replacing Blue Spruce as State Tree". BYU Daily Universe. Brigham Young University. Archived from the original on 3 June 2024. Retrieved 25 September 2024.
  66. ^ Wood, Benjamin (26 March 2024). "Student-advocated state tree bill signed into law". Deseret News. Monroe, Utah. Archived from the original on 23 November 2022.
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