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hemlock dwarf mistletoe

Scientific Name: Arceuthobium tsugense ssp. tsugense

Family: Viscaceae

Category: Dicot

Growth: Shrub, Subshrub

Duration: Perennial

Other Names:

       

Hemlock Dwarf Mistletoe (Arceuthobium tsugense)

Hemlock dwarf mistletoe, scientifically known as Arceuthobium tsugense, is a parasitic plant primarily affecting western hemlock trees.

Taxonomy and Nomenclature

  • Scientific Name: Arceuthobium tsugense
  • Synonyms: Arceuthobium tsugense (Rosendahl) G.N. Jones
  • Family: Viscaceae
  • Subspecies:
    • Arceuthobium tsugense subsp. tsugense
    • Arceuthobium tsugense subsp. mertensianae Hawksw. & Nickrent
    • Arceuthobium tsugense subsp. amabilae Mathiasen

Distribution and Habitat

  • This dwarf mistletoe is primarily found in coastal regions, specifically within western hemlock stands. It's noted that outside a few areas in the Prince Rupert Forest Region, it's mainly a coastal, rather than interior, species.
  • It is found in mature and old-growth Douglas-fir forests as well.
  • Observed in mixed conifer stands in Washington and Oregon.

Ecological Role

  • Arceuthobium tsugense is a hemiparasite, meaning it obtains some nutrients from its host plant (western hemlock) but can also perform photosynthesis.
  • Infection by hemlock dwarf mistletoe can lead to reduced tree growth and vigor, and decreased wood quality.
  • Its presence can cause the formation of "witches' brooms" - dense clusters of branches - on infected trees.

Morphological Characteristics and Growth Habits

  • Dwarf mistletoes are parasitic flowering plants that grow on stems and branches.
  • Infection starts with small branch swellings, which is the first indication of its presence.
  • Heavy infestations can cause broken branches due to the weight of large witches' brooms.
  • Can cause large stem swelling on hemlock.

Interactions with Other Organisms

  • The primary host for Arceuthobium tsugense is western hemlock (Tsuga heterophylla).
  • It can also infect western white pine (Pinus).

Further Information

  • Smith, R. B. Assessing Dwarf Mistletoe on Western Hemlock. Forest Science, Volume 15, Number 3, 1 September 1969, pp. 277-285(9).
  • Rocky Mountain Forest and Range Experiment Station, U.S. Department of Agriculture, 1994 - Dwarf mistletoes.
  • Images are available from Plantwise and partners for hemlock dwarf mistletoe.