Very-closely related to sister-species balsam poplar  Populus balsamifera.   So close, that some sources call this plant a subspecies of the sister-species, Populus balsamifera subsp. trichocarpa.

Both are part of aspen/​cottonwood/​poplar  genus Populus in willow  family Salicaceae.

Native to western 🇨🇦 Canada and 🇺🇸 USA, from Alaska and British Columbia, to the Pacific Northwest, Rocky Mountains and California.   ▭ 🌎︎ Map (Western North America).  Adobe Acrobat Reader file

In the North and East of this range, black cottonwood overlaps with a very-closely related sister-species balsam poplar  Populus balsamifera, which then extends further North, West and East, into Alaska, the Great Lakes and East.  Some ▭ maps confuse or combine these two sister-species.

Uses by native peoples
(Ethnobotany database)

Populus hosts caterpillars of 367 species
of butterflies and moths, in some areas.
  This plant is also known to be a host for (in areas where invasive) 🐝︎ spotted lanternfly (SLF)  Lycorma delicatula.

Often grows in clonal colonies [1] —look around for other stems!

In areas where this plant is native, this plant is among the wet-loving (but terrestrial ) shrubs and trees used to protect eroding streambanks, lakeshores, bluffs, road slopes and landslides (as well as floodplains and stormwater detention ponds), in a process called live-staking.

Propagation protocol.  Adobe Acrobat Reader file   USFS propagation protocol.

Learn more about ◼︎ black cottonwood Populus trichocarpa

🔍︎ 🔍︎ images Discover Life Encyclopedia of Life Flora of North America NRCS PLANTS db Silvics USFS USFS plant of the week Wikipedia