Western/Plains Cottonwood (Populus deltoides ssp. monilifera)

western/plains cottonwood
General Appearance
  • Has an open, spreading crown.
  • Bark is smooth and yellowish-grey in colour; as the tree matures, the bark gets rougher and more furrowed.
  • Is a medium-sized to large tree, attaining heights up to 30 metres (98.4 feet).
  • Male and female catkins produced on separate trees, form before leaves develop in spring.
  • Staminate (male) catkins, reddish ? purple in colour, 8 to 10 centimetres (3.14 to 3.94 inches) long with 40 to 60 stamens.
  • Pistillate (female) catkins, green in colour, 9 to 15 centimetres (3.54 to 5.91 inches) long.
  • Found on mature pistillate catkins, small, egg-shaped, green in colour, 15 to 25 centimetres (5.91 to 11.81 inches) long.
  • Simple, triangular or heart shaped, 5 to 10 centimetres (1.97 to 3.94 inches) long and 4 to 11 centimetres (1.57 to 4.33 inches) wide.
  • Rounded teeth with a short tip without teeth.
  • Glossy, bright green above, slightly paler on underside.
  • Distributed within Southern Alberta along riparian valleys of the Oldman River and its tributaries.
Natural History

  • Commonly found along riparian areas with adequate moisture and soil rich from periodic flooding of the river.
When Active
  • Is perennial, lifespan can range from 100 to 150 years.
  • Catkins produced in early spring before leaves appear.
  • Pistillate (female) catkins mature and release seed for up to three weeks in early summer.
Reproduction and Growth
  • Able to reproduce sexually and asexually.
  • Reproduces asexually by sprouting new shoots from roots, stems or branches that have broken off.
  • Sexual reproduction through staminate and pistillate catkins.
  • Staminate (male) catkins release their pollen in the early spring.
  • Pistillate (female) catkins, once pollinated, develop small, green fruits 15 to 30 centimetres (5.91 to 11.81 inches) long.
  • Fruit opens up in early summer, when river flows are at their highest, to release an abundant supply of seeds attached to cotton-like strands.
  • High river flows form moist sand bars or silt beds that are necessary for germination because cottonwood seeds are unable to out-compete weeds and other plants. These locations also provide ideal sites for asexual reproduction from plant parts.
  • Germination sites must remain moist and receive lots of sunlight in order for germination to occur.
  • Seeds remain viable for two to four weeks and must germinate during this time.
  • Seeds, together with cotton-like strands are continuously released for up to three weeks, thus resulting in the common name of "Cottonwood".
Conservation and Management

Status Issues
  • Cottonwoods are heavily dependent upon the natural cycle of flooding in order to grow and thrive.
  • Altering river flows for dams, drought conditions within Southern Alberta and growing city populations are all factors that can limit the success of Cottonwoods.

For more information about the content of this document, contact For-Info@gov.ab.ca
This information published to the web on March 30, 2016.
Last Reviewed/Revised on March 16, 2018.