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Arceuthobium microcarpum

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Arceuthobium microcarpum
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Order: Santalales
Family: Santalaceae
Genus: Arceuthobium
Species:
A. microcarpum
Binomial name
Arceuthobium microcarpum
(Engelm.) Hawksw. & Wiens
Synonyms

Arceuthobium douglasii var. microcarpum Engelm. in Rothr. Arceuthobium campylopodum subsp. microcarpum (Engelm.) Nickrent Razoumofskya microcarpa (Engelm.) Wooton & Standl.

Arceuthobium microcarpum is a species of dwarf mistletoe endemic to Arizona and New Mexico. It has two subspecies: A. microcarpum subsp. microcarpum, commonly known as western spruce dwarf mistletoe, which parasitizes spruce trees (Picea engelmannii and Picea pungens), and A. microcarpum subsp. aristatae, commonly known as bristlecone pine dwarf mistletoe, which parasitizes Rocky Mountain bristlecone pine trees (Pinus aristata). Populations of A. microcarpum significantly impact the ecology of the conifer forests where they occur, decreasing the vitality and reproductive rate of host trees and creating microhabitats for wildlife by inducing the formation of witch's brooms.

Distribution

A. microcarpum is a high elevation species, occurring in conifer forests at elevations of 2400-3200 meters.[1] Unlike its host species, which extend northward through the Rocky Mountains, A. microcarpum occurs only in Arizona and New Mexico.[1] A. microcarpum subsp. microcarpum is well-documented in the White Mountains of Arizona, the North Rim of the Grand Canyon, the San Francisco Peaks of Arizona, the Pinaleño Mountains of Arizona, the Mogollon Mountains of New Mexico, and the Sacramento Mountains of New Mexico.[2] The geographic range of A. microcarpum subsp. aristatae is much narrower: it is known only from a few locations in Coconino County, Arizona, including Schultz Mountain in the San Francisco Peaks and Kendrick Peak.[2]

Conservation

Because of its limited range, NatureServe considers A. microcarpum imperiled (T2).[3] However, the species has no state or federal-level protections. Fires, including the Wallow Fire in the White Mountains or Arizona, have eradicated or reduced some populations of A. microcarpum.[2]

Ecology

All dwarf mistletoes negatively impact the vigor, longevity, and reproductive rate of their hosts, but A. microcarpum infections cause some of the highest mortality rates within the genus. For example, at sites where Picea pungens trees are heavily infected, seedling mortality is twice as high as at uninfected sites.[4] A study in the White Mountains of Arizona found that in stands of severely infected Picea pungens and Picea engelmannii, 20-35% of trees were dead, and half of the dead trees showed signs of the highest level of mistletoe infection.[5] Mortality of infected trees is often compounded by the impact of defoliation by Elatobium abietinum, an invasive species of aphid that feeds on spruce.[6]

Host trees often respond to infection by A. microcarpum by exhibiting abnormal growth patterns, including the formation of witch's brooms.[7] The witch's brooms induced by this mistletoe species are typically small and dense but can be numerous: a heavily infected tree may bear hundreds of brooms.[8] Broom formation reduces seed production by the host plant and is associated with decreased longevity, but it increases available nutrients to the mistletoe.[7] Brooms also provide important microhabitats, serving as nesting sites for birds and small mammals.[7]

In an example of hyperparasitism, at least two species of fungi have been documented parasitizing A. microcarpum, namely Colletotrichum gloeosporioides and Cylindrocarpon gillii.[9] Infection by C. gillii (formerly known as Septogloeum gillii) is characterized by yellowish-white lesions on the stems that enlarge and erupt into masses of white spores, typically killing the mistletoe shoots.[10] Infection by C. gloeosporioides causes black lesions at stem nodes, eventually leading to dieback.[9]

Dwarf mistletoes have been identified as a food source for arthropods, birds, and mammals.[7] In particular, Abert's squirrel has been documented feeding on A. microcarpum.[11]

Taxonomy

The type specimen of A. microcarpum was collected by Grove Karl Gilbert in 1873, growing on Picea engelmannii in Apache County, Arizona.[12] In 1879, George Engelmann gave the first formal description of the taxon, as A. douglasii var. microcarpum; the specific epithet microcarpum refers to the berries, which are among the smallest of any north American members of the genus.[13] In 1970, Frank Hawksworth and Delbert Wiens recombined the taxon as A. microcarpum, elevating it to the species level.[14] Jared M. Scott collected the type specimen for A. microcarpum subsp. aristatae in 2006 from near the summit of Schultz Peak in Arizona, where it was growing on Pinus aristata.[15] Together with Robert Mathiasen, Scott formally described A. microcarpum subsp. aristatae in 2009.

Arceuthobium microcarpum (Engelm.) Hawksw. & Wiens, Brittonia 22(3): 268. 1970.[14] = Arceuthobium douglasii var. microcarpum Engelm. in Rothr., Rep. U.S. Geogr. Surv., Wheeler vol. 6, Botany 253. 1879.[13] = Arceuthobium campylopodum subsp. microcarpum (Engelm.) Nickrent, Phytoneuron 2012–51: 10. 2012.[16] = Razoumofskya microcarpa (Engelm.) Wooton & Standl., Contr. U.S. Natl. Herb. 19: 179. 1915.[17]

References

  1. ^ a b "Arceuthobium campylopodum subsp. microcarpum - FNA". dev.floranorthamerica.org. Retrieved 2025-11-01.
  2. ^ a b c Mathiasen, Robert L. (2021). Mistletoes of the Continental United States and Canada. Botanical miscellany. Fort Worth, Texas: BRIT Press. pp. 87–91. ISBN 978-1-889878-66-9.
  3. ^ "NatureServe Explorer 2.0". explorer.natureserve.org. Retrieved 2025-11-01.
  4. ^ Mathiasen, Robert L. (1986). "Infection of Young Douglas-Firs and Spruces by Dwarf Mistletoes in the Southwest". The Great Basin Naturalist. 46 (3): 528–534. ISSN 0017-3614.
  5. ^ Mathiasen, Robert L.; Hawksworth, Frank G.; Edminster, Carleton B. (1986). "Effects of Dwarf Mistletoe on Spruce in the White Mountains, Arizona". The Great Basin Naturalist. 46 (4): 685–689. ISSN 0017-3614.
  6. ^ Lynch, Ann M. (2004). "Fate and Characteristics of Picea Damaged by Elatobium Abietinum (walker) (homoptera: Aphididae) in the White Mountains of Arizona". Western North American Naturalist. 64 (1): 7–17. ISSN 1527-0904.
  7. ^ a b c d Tinnin, Robert O.; Hawksworth, Frank G.; Knutson, Donald M. (1982). "Witches' Broom Formation in Conifers Infected by Arceuthobium spp.: An Example of Parasitic Impact upon Community Dynamics". The American Midland Naturalist. 107 (2): 351–359. doi:10.2307/2425385. ISSN 0003-0031.
  8. ^ Geils, Brian W; Cibrián Tovar, Jose; Moody, Benjamin (2002). Mistletoes of North American Conifers (PDF) (Gen. Tech. Rep. RMRS–GTR–98. ed.). Ogden, Utah: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. pp. 48–40, 57–65.
  9. ^ a b Hawksworth, Frank; Wicker, Ed; Scharpf, Robert (April 1977). "Fungal Parasites of Dwarf Mistletoes" (PDF). Rocky Mountain Forest and Range Experiment Station, Forest Service, USDA. 36.
  10. ^ Ellis, Don E. (1946). "Anthracnose of Dwarf Mistletoe Caused by a New Species of Septogloeum". Journal of the Elisha Mitchell Scientific Society. 62 (1): 25–50. ISSN 0013-6220.
  11. ^ Edelman, Andrew J.; Koprowski, John L. (2005). "Diet and Tree Use of Abert's Squirrels (Sciurus aberti) in a Mixed-Conifer Forest". The Southwestern Naturalist. 50 (4): 461–465. ISSN 0038-4909.
  12. ^ Hawksworth, Frank G.; Wiens, Delbert (1970). "New Taxa and Nomenclatural Changes in Arceuthobium (Viscaceae)". Brittonia. 22 (3): 265–269. doi:10.2307/2805908. ISSN 0007-196X.
  13. ^ a b Rothrock, J.T. Report Upon United States Geographical Surveys West of the One Hundredth Meridian, in Charge of First Lieut. Geo. M. Wheeler ... vol. 6, Botany 253. 1879.
  14. ^ a b Hawksworth, Frank G.; Wiens, Delbert (1970). "New Taxa and Nomenclatural Changes in Arceuthobium (Viscaceae)". Brittonia. 22 (3): 265–269. doi:10.2307/2805908. ISSN 0007-196X.
  15. ^ Scott, Jared M.; Mathiasen, Robert L. (2009). "Bristlecone Pine Dwarf Mistletoe: Arceuthobium Microcarpum Subsp. Aristatae (viscaceae), a New Subspecies of Western Spruce Dwarf Mistletoe from Northern Arizona". Journal of the Botanical Research Institute of Texas. 3 (1): 13–21. ISSN 1934-5259.
  16. ^ Nickrent, D.L. Phytoneuron 2012–51: 10. 2012.
  17. ^ Wooton, E.O., & P.C. Standley. Contributions from the United States National Herbarium 19: 179. 1915.
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