Thuja occidentalis

Photo Credit: © Paul Tavares via iNaturalist.org. Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) License; https://creativecommons.org/licenses/by-nc/4.0/.
Thuja occidentalis
Common Name: arborvitae
Other Common Names: cèdre-thuya occidental, eastern white cedar, northern white cedar, swamp cedar, thuier cèdre
Plant Functional Group: Evergreen conifer
Class > Order > Family: Pinopsida > Pinales > Cupressaceae
Where is the species found?
States & Provinces
CT, IA, IL, IN, KY, MA, MB, MD, ME, MI, MN, NB, NC, NH, NJ, NS, NY, OH, ON, PA, PE, QC, RI, SC, TN, VA, VT, WI, WV
Which phenophases should I observe?
Do you see...?
Pollen cones Pollen cones
One or more fresh, male pollen cones (strobili) are visible on the plant. Cones have overlapping scales that are initially tightly closed, then spread apart to open the cone and release pollen. Include cones that are unopened or open, but do not include wilted or dried cones that have already released all of their pollen.
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How many fresh pollen cones are present?

  • Less than 3
  • 3 to 10
  • 11 to 100
  • 101 to 1,000
  • 1,001 to 10,000
  • More than 10,000
Open pollen cones
One or more open, fresh, male pollen cones (strobili) are visible on the plant. Cones are considered "open" when the scales have spread apart to release pollen. Do not include wilted or dried cones that have already released all of their pollen.

What percentage of all fresh pollen cones (unopened plus open) on the plant are open?

  • Less than 5%
  • 5-24%
  • 25-49%
  • 50-74%
  • 75-94%
  • 95% or more
Pollen release
One or more male cones (strobili) on the plant release visible pollen grains when gently shaken or blown into your palm or onto a dark surface.
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How much pollen is released?

  • Little: Only a few grains are released.
  • Some: Many grains are released.
  • Lots: A layer of pollen covers your palm, or a cloud of pollen can be seen in the air when the wind blows

Seed cones Unripe seed cones
One or more unripe, female seed cones are visible on the plant. For Thuja occidentalis, an unripe seed cone is green or yellow-green with scales closed together.
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How many seed cones are unripe?

  • Less than 3
  • 3 to 10
  • 11 to 100
  • 101 to 1,000
  • 1,001 to 10,000
  • More than 10,000
Ripe seed cones
One or more ripe, female seed cones are visible on the plant. For Thuja occidentalis, a seed cone is considered ripe when it has turned tan or brown and the scales have begun to spread apart to expose the seeds inside. Do not include empty cones that have already dropped all of their seeds.
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How many seed cones are ripe?

  • Less than 3
  • 3 to 10
  • 11 to 100
  • 101 to 1,000
  • 1,001 to 10,000
  • More than 10,000
Recent cone or seed drop
One or more seed cones or seeds have dropped or been removed from the plant since your last visit. Do not include empty seed cones that had long ago dropped all of their seeds but remained on the plant.
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How many seed cones have dropped seeds or have completely dropped or been removed from the plant since your last visit?

  • Less than 3
  • 3 to 10
  • 11 to 100
  • 101 to 1,000
  • 1,001 to 10,000
  • More than 10,000
What do these phenophases look like?

There is currently no photoguide available for this species. If you'd like help us create one, use the guidance document and species template provided here. Then send it via email to education@usanpn.org when it is complete.

ITIS information for arborvitae (ITIS TSN: 505490 )
USDA PLANTS profile for arborvitae (USDA Symbol: THOC2 )