''Populus trichocarpa'', the black cottonwood, western balsam-poplar or California poplar, is a

deciduous In the fields of horticulture and botany, the term deciduous () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed Leaf, leaves, usually in the autumn; to the shedding of petals, aft ...

broadleaf tree species native to western

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

. It is used for

timber Lumber is wood that has been processed into uniform and useful sizes (dimensional lumber), including beams and planks or boards. Lumber is mainly used for construction framing, as well as finishing (floors, wall panels, window frames). ...

, and is notable as a

model organism A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workings of other organisms. Mo ...

plant biology Botany, also called plant science, is the branch of natural science Natural science or empirical science is one of the branches of science concerned with the description, understanding and prediction of natural phenomena, based on empiri ...

. The tree is notable for the seed-carrying cottony fluff it releases into the air each spring.

Description

It is a large tree, growing to a height of and a trunk diameter over . It ranks 3rd in poplar species in the American Forests Champion Tree Registry. It is normally fairly short-lived, but some trees may live up to 400 years. A cottonwood in Willamette Mission State Park near

Salem, Oregon Salem ( ) is the List of capitals in the United States, capital city of the U.S. state of Oregon, and the county seat of Marion County, Oregon, Marion County. It is located in the center of the Willamette Valley alongside the Willamette River, w ...

, holds the national and world records. Last measured in April 2008, this black cottonwood was found to be standing at tall, around, with 527 points. The

bark Bark may refer to: Common meanings * Bark (botany), an outer layer of a woody plant such as a tree or stick * Bark (sound), a vocalization of some animals (which is commonly the dog) Arts and entertainment * ''Bark'' (Jefferson Airplane album), ...

is grey and covered with

lenticel A lenticel is a porous tissue consisting of cells with large intercellular spaces in the periderm of the secondarily thickened organs and the Bark (botany), bark of woody stems and roots of gymnosperms and dicotyledonous flowering plants. It func ...

s, becoming thick and deeply fissured on old trees. The bark can become hard enough to cause sparks when cut with a chainsaw.Ewing, Susan. The Great Alaska Nature Factbook. Portland: Alaska Northwest Books, 1996. The stem is grey in the older parts and light brown in younger parts. The

crown A crown is a traditional form of head adornment, or hat, worn by monarchs as a symbol of their power and dignity. A crown is often, by extension, a symbol of the monarch's government or items endorsed by it. The word itself is used, parti ...

is usually roughly conical and quite dense. In large trees, the lower branches droop downwards. Spur shoots are common. The

wood Wood is a structural tissue/material found as xylem in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulosic fibers that are strong in tension and embedded in a matrix of lignin t ...

has a light coloring and a straight grain. The

leaves A leaf (: leaves) is a principal appendage of the stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, stem, ...

are usually long with a glossy, dark green upper side and glaucous, light grey-green underside; larger leaves may be up to long and may be produced on stump sprouts and very vigorous young trees. The leaves are alternate, elliptical with a crenate margin and an acute tip, and reticulate venation. The petiole is reddish. The

bud In botany, a bud is an undeveloped or Plant embryogenesis, embryonic Shoot (botany), shoot and normally occurs in the axil of a leaf or at the tip of a Plant stem, stem. Once formed, a bud may remain for some time in a dormancy, dormant conditi ...

s are conical, long, narrow, and sticky, with a strong balsam scent in spring when they open. ''P. trichocarpa'' has an extensive and aggressive root system, which can invade and damage drainage systems. Sometimes, the roots can even damage the foundations of buildings by drying out the soil. In 2016, the first direct evidence was published indicating that wild ''P. trichocarpa'' fixes nitrogen. Populus trichocarpa 3

Populus trichocarpa mature female catkins bursting open

Reproduction

Flowering and fruiting

Black cottonwood male catkin and leaf buds

''P. trichocarpa'' is normally

dioecious Dioecy ( ; ; adj. dioecious, ) is a characteristic of certain species that have distinct unisexual individuals, each producing either male or female gametes, either directly (in animals) or indirectly (in seed plants). Dioecious reproduction is ...

; male and female

catkin A catkin or ament is a slim, cylindrical flower cluster (a spike), with inconspicuous or no petals, usually wind- pollinated ( anemophilous) but sometimes insect-pollinated (as in '' Salix''). It contains many, usually unisexual flowers, arra ...

s are borne on separate trees. The species reaches

flowering Flowers, also known as blooms and blossoms, are the reproductive structures of flowering plants ( angiosperms). Typically, they are structured in four circular levels, called whorls, around the end of a stalk. These whorls include: calyx, m ...

age around 10 years. Flowers may appear in early March to late May in Washington and

Oregon Oregon ( , ) is a U.S. state, state in the Pacific Northwest region of the United States. It is a part of the Western U.S., with the Columbia River delineating much of Oregon's northern boundary with Washington (state), Washington, while t ...

, and sometimes as late as mid-June in northern and interior

British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...

Idaho Idaho ( ) is a landlocked U.S. state, state in the Pacific Northwest and Mountain states, Mountain West subregions of the Western United States. It borders Montana and Wyoming to the east, Nevada and Utah to the south, and Washington (state), ...

, and

Montana Montana ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Idaho to the west, North Dakota to the east, South Dakota to the southeast, Wyoming to the south, an ...

. Staminate catkins contain 30 to 60

stamen The stamen (: stamina or stamens) is a part consisting of the male reproductive organs of a flower. Collectively, the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filament ...

s, elongated to 2 to 3 cm, and are

. The pollen can be an

allergen An allergen is an otherwise harmless substance that triggers an allergic reaction in sensitive individuals by stimulating an immune response. In technical terms, an allergen is an antigen that is capable of stimulating a type-I hypersensitivi ...

. Pistillate catkins at maturity are 8 to 20 cm long with rotund-ovate, tricarpellate subsessile fruits 5 to 8 mm long. Each capsule contains many minute

seed In botany, a seed is a plant structure containing an embryo and stored nutrients in a protective coat called a ''testa''. More generally, the term "seed" means anything that can be Sowing, sown, which may include seed and husk or tuber. Seeds ...

s with long, white, cottony hairs.

Seed production and dissemination

The seed ripens and is disseminated by late May to late June in Oregon and Washington, but frequently not until mid-July in Idaho and Montana. Abundant seed crops are usually produced every year. Attached to its cotton, the seed is light and buoyant and can be transported long distances by wind and water. Although highly viable, longevity of ''P. trichocarpa'' seed under natural conditions may be as short as two weeks to a month. This can be increased with cold storage. Seeds and Fluff of Cottonwood

Seedling development

Moist seedbeds are essential for high germination, and seedling survival depends on continuously favorable conditions during the first month. Wet bottomlands of rivers and major streams frequently provide such conditions, particularly where bare soil has been exposed or new soil laid down. Germination is epigeal (above ground). ''P. trichocarpa'' seedlings do not usually become established in abundance after

logging Logging is the process of cutting, processing, and moving trees to a location for transport. It may include skidder, skidding, on-site processing, and loading of trees or trunk (botany), logs onto logging truck, trucksabscise shoots complete with green leaves. These shoots drop to the ground and may root where they fall or may be dispersed by water transport. In some situations, abscission may be one means of colonizing exposed

sandbar In oceanography, geomorphology, and geoscience, a shoal is a natural submerged ridge, bank, or bar that consists of, or is covered by, sand or other unconsolidated material, and rises from the bed of a body of water close to the surface or ...

Taxonomy

"''Trichocarpa''" is Greek for "hairy fruits". These scientific names are now considered synonymous with ''P. trichocarpa'':

Distribution and habitat

The native range of ''P. trichocarpa'' covers large sections of western

. It extends from

Southeast Alaska Southeast Alaska, often abbreviated to southeast or southeastern, and sometimes called the Alaska(n) panhandle, is the southeastern portion of the U.S. state of Alaska, bordered to the east and north by the northern half of the Canadian provi ...

Kodiak Island Kodiak Island (, ) is a large island on the south coast of the U.S. state of Alaska, separated from the Alaska mainland by the Shelikof Strait. The largest island in the Kodiak Archipelago, Kodiak Island is the second largest island in the Un ...

and

Cook Inlet Cook Inlet (; Sugpiaq language, Sugpiaq: ''Cungaaciq'') stretches from the Gulf of Alaska to Anchorage, Alaska, Anchorage in south-central Alaska. Cook Inlet branches into the Knik Arm and Turnagain Arm at its northern end, almost surrounding ...

latitude In geography, latitude is a geographic coordinate system, geographic coordinate that specifies the north-south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from −90° at t ...

62° 30° N., through British Columbia and the forested areas of Washington and Oregon, to the mountains in southern

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

and northern

Baja California Baja California, officially the Free and Sovereign State of Baja California, is a state in Mexico. It is the northwesternmost of the 32 federal entities of Mexico. Before becoming a state in 1952, the area was known as the North Territory of B ...

(31°N). It is also found inland, generally on the west side of the

Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in great-circle distance, straight-line distance from the northernmost part of Western Can ...

, in British Columbia, southwestern

Alberta Alberta is a Provinces and territories of Canada, province in Canada. It is a part of Western Canada and is one of the three Canadian Prairies, prairie provinces. Alberta is bordered by British Columbia to its west, Saskatchewan to its east, t ...

, western Montana, and north-to-central Idaho. Scattered small populations have been noted in southeastern Alberta, eastern Montana, western

North Dakota North Dakota ( ) is a U.S. state in the Upper Midwest, named after the indigenous Dakota people, Dakota and Sioux peoples. It is bordered by the Canadian provinces of Saskatchewan and Manitoba to the north and by the U.S. states of Minneso ...

, western

Wyoming Wyoming ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States, Western United States. It borders Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho t ...

Utah Utah is a landlocked state in the Mountain states, Mountain West subregion of the Western United States. It is one of the Four Corners states, sharing a border with Arizona, Colorado, and New Mexico. It also borders Wyoming to the northea ...

, and

Nevada Nevada ( ; ) is a landlocked state in the Western United States. It borders Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the seventh-most extensive, th ...

. Black cottonwood grows on alluvial sites, riparian habitats, and moist woods on mountain slopes, from sea level to elevations of . It often forms extensive stands on bottomlands of major streams and rivers at low elevations along the Pacific Coast, west of the Cascade Range. In eastern Washington and other dry areas, it is restricted to protected valleys and canyon bottoms, along streambanks, and edges of ponds and meadows. It grows on a variety of soils from moist silts, gravels, and sands to rich humus, loams, and occasionally clays. Black cottonwood is a pioneer species that grows best in full sunlight and commonly establishes on recently disturbed alluvium. Seeds are numerous and widely dispersed because of their cottony tufts, enabling the species to colonize even burn sites, if conditions for establishment are met. Seral communities dominated or codominated by cottonwood are maintained by periodic flooding or other types of soil disturbance. Black cottonwood has low drought tolerance; it is flood-tolerant but cannot tolerate brackish water or stagnant pools. ''P. trichocarpa'' has been one of the most successful introductions of trees to the otherwise almost treeless

Faroe Islands The Faroe Islands ( ) (alt. the Faroes) are an archipelago in the North Atlantic Ocean and an autonomous territory of the Danish Realm, Kingdom of Denmark. Located between Iceland, Norway, and the United Kingdom, the islands have a populat ...

. The species was imported from Alaska to

Iceland Iceland is a Nordic countries, Nordic island country between the Atlantic Ocean, North Atlantic and Arctic Oceans, on the Mid-Atlantic Ridge between North America and Europe. It is culturally and politically linked with Europe and is the regi ...

in 1944 and has since become one of the most widespread trees in the country.

Ecology

Although the most populous cottonwood of the

Pacific Northwest The Pacific Northwest (PNW; ) is a geographic region in Western North America bounded by its coastal waters of the Pacific Ocean to the west and, loosely, by the Rocky Mountains to the east. Though no official boundary exists, the most common ...

, it hybridizes with the region's three other species: balsam poplar, plains cottonwood, and narrowleaf cottonwood; all four have similar appearances and provide habitats for various animals. Cottonwoods are shade intolerant. Black cottonwood thrives by colonizing disturbed sites, but can be replaced by conifers. The wood is relatively weak and waterlogged, often splitting during freezes. It is susceptible to rot as well. Woodpeckers create cavities which various animals can use for nests. Larger birds nest in the large upper branches. Beavers use the trees as food and dam-building material.

Cultivation

It is grown as an

ornamental tree Ornamental plants or ''garden plants'' are plants that are primarily grown for their beauty but also for qualities such as scent or how they shape physical space. Many flowering plants and garden varieties tend to be specially bred cultivars th ...

, valued for its fast growth and scented foliage in spring, detectable from over 100 m distance. The roots are however invasive, and it can damage the foundations of buildings on shrinkable clay soils if planted nearby (Mitchel 1996). Branches can be added to potted plants to stimulate rooting.

Uses

Traditional

The tree was and is significant for many Native American tribes of the Western United States. Some Native Americans consumed cottonwood inner bark and sap, feeding their horses the inner bark and foliage. The wood, roots and bark have been used for firewood, canoe making, rope, fish traps, baskets and structures. The gum-like sap was used as a glue or as waterproofing.Pojar, J. & MacKinnon, A. Plants of the Pacific Northwest Coast. Vancouver, British Columbia: Lone Pine Publishing, 2004. The Quinault used it for post wood. The Cowlitz made the base (hearth board) of their fire-making tool, a bow drill, with its wood. The Squaxin cut young branches for building sweat lodges.

Medicinal

The tree had medicinal value as well. The Squaxin used the bark for sore throats and for the treatment of tuberculosis, as well as water and the bruised leaves as an antiseptic mixture. The Klallam used the buds for an eye treatment. For the Quinault, they extracted gum from the burls and applied it to cuts on the skin.

Modern

Commercial extracts are produced from the fragrant buds for use as a perfume in

cosmetics Cosmetics are substances that are intended for application to the body for cleansing, beautifying, promoting attractiveness, or altering appearance. They are mixtures of chemical compounds derived from either Natural product, natural source ...

. The shredded and heat treated wood is sold a pet snake bedding material, with its softness, water absorbency, and low maintenance described as its primary properties.

Lumber

''P. trichocarpa'' wood is light-weight and although not particularly strong, is strong for its weight. The wood material has short, fine

cellulose Cellulose is an organic compound with the chemical formula, formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of glycosidic bond, β(1→4) linked glucose, D-glucose units. Cellulose is an important s ...

fibres that are used in pulp for high-quality book and magazine

paper Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, Textile, rags, poaceae, grasses, Feces#Other uses, herbivore dung, or other vegetable sources in water. Once the water is dra ...

. The wood is also excellent for production of

plywood Plywood is a composite material manufactured from thin layers, or "plies", of wood veneer that have been stacked and glued together. It is an engineered wood from the family of manufactured boards, which include plywood, medium-density fibreboa ...

. Living trees are used as

windbreak A windbreak (shelterbelt) is a planting usually made up of one or more rows of trees or shrubs planted in such a manner as to provide shelter from the wind and to protect soil from erosion. They are commonly planted in hedgerows around the ed ...

s. This species grows very quickly; trees in

plantation Plantations are farms specializing in cash crops, usually mainly planting a single crop, with perhaps ancillary areas for vegetables for eating and so on. Plantations, centered on a plantation house, grow crops including cotton, cannabis, tob ...

s in Great Britain have reached tall in 11 years, and tall in 28 years. It can reach suitable size for pulp production in 10–15 years and about 25 years for

production.

As a model species

''Populus trichocarpa'' has several qualities that makes it a good model species for trees: * Model genome size (although significantly larger than the other model plant, ''

Arabidopsis thaliana ''Arabidopsis thaliana'', the thale cress, mouse-ear cress or arabidopsis, is a small plant from the mustard family (Brassicaceae), native to Eurasia and Africa. Commonly found along the shoulders of roads and in disturbed land, it is generally ...

'') * Rapid growth (for a tree) * Reaches reproductive maturity 4–6 years * Economically important * It represents a phenotypically diverse genus For these reasons, the species has been extensively studied. Its

genome A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as ...

sequence was published in 2006. More than 121,000

expressed sequence tag In genetics, an expressed sequence tag (EST) is a short sub-sequence of a cDNA sequence. ESTs may be used to identify gene transcripts, and were instrumental in gene discovery and in gene-sequence determination. The identification of ESTs has pro ...

s have been

sequenced In genetics and biochemistry, sequencing means to determine the primary structure (sometimes incorrectly called the primary sequence) of an unbranched biopolymer. Sequencing results in a symbolic linear depiction known as a sequence which succi ...

from it. The wide range of topics studied by using ''P. trichocarpa'' include the effects of

ethylene Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon–carbon bond, carbon–carbon doub ...

lignin Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidit ...

biosynthesis Biosynthesis, i.e., chemical synthesis occurring in biological contexts, is a term most often referring to multi-step, enzyme-Catalysis, catalyzed processes where chemical substances absorbed as nutrients (or previously converted through biosynthe ...

, drought tolerance, and wood formation.

Cultural significance

The Chehalis believed that the tree was intelligent and had a form of special physical agency, moving on its own without the need of wind. Due to this belief, they refused to use it for firewood.

Genome

The sequence of ''P. trichocarpa'' is that of an individual

female An organism's sex is female ( symbol: ♀) if it produces the ovum (egg cell), the type of gamete (sex cell) that fuses with the male gamete (sperm cell) during sexual reproduction. A female has larger gametes than a male. Females and ...

specimen "Nisqually-1", named after the Nisqually River in Washington, where the specimen was collected. The sequencing was performed at the

Joint Genome Institute The Joint Genome Institute (JGI) is a scientific user facility for integrative genomic science at Lawrence Berkeley National Laboratory. The mission of the JGI is to advance genomics research in support of the United States Department of Energy ...

using the

shotgun A shotgun (also known as a scattergun, peppergun, or historically as a fowling piece) is a long gun, long-barreled firearm designed to shoot a straight-walled cartridge (firearms), cartridge known as a shotshell, which discharges numerous small ...

method. The depth of the sequencing was about 7.5 x (meaning that each

base pair A base pair (bp) is a fundamental unit of double-stranded nucleic acids consisting of two nucleobases bound to each other by hydrogen bonds. They form the building blocks of the DNA double helix and contribute to the folded structure of both DNA ...

was sequenced on average 7.5 times). Genome annotation was done primarily by the Joint Genome Institute, the

Oak Ridge National Laboratory Oak Ridge National Laboratory (ORNL) is a federally funded research and development centers, federally funded research and development center in Oak Ridge, Tennessee, United States. Founded in 1943, the laboratory is sponsored by the United Sta ...

, the Umeå Plant Science Centre, and Genome Canada. Prior to the publication of ''P. trichocarpa'' genome the only available plant genomes were those of

thale cress ''Arabidopsis thaliana'', the thale cress, mouse-ear cress or arabidopsis, is a small plant from the mustard family (Brassicaceae), native to Eurasia and Africa. Commonly found along the shoulders of roads and in disturbed land, it is generally ...

and

rice Rice is a cereal grain and in its Domestication, domesticated form is the staple food of over half of the world's population, particularly in Asia and Africa. Rice is the seed of the grass species ''Oryza sativa'' (Asian rice)—or, much l ...

, both of which are

herbaceous Herbaceous plants are vascular plants that have no persistent woody stems above ground. This broad category of plants includes many perennials, and nearly all annuals and biennials. Definitions of "herb" and "herbaceous" The fourth edition of ...

. ''P. trichocarpa'' is the first woody plant genome to be sequenced. Considering the economic importance of wood and wood products, the availability of a tree genome was necessary. The sequence also allows evolutionary comparisons and the elucidation of basic molecular differences between herbaceous and woody plants.

Characteristics

* Size: 485 million

s (human genome: 3 billion base pairs) * Proportion of

heterochromatin Heterochromatin is a tightly packed form of DNA or '' condensed DNA'', which comes in multiple varieties. These varieties lie on a continuum between the two extremes of constitutive heterochromatin and facultative heterochromatin. Both play a rol ...

euchromatin Euchromatin (also called "open chromatin") is a lightly packed form of chromatin (DNA, RNA, and protein) that is enriched in genes, and is often (but not always) under active transcription. Euchromatin stands in contrast to heterochromatin, which ...

: 3:7 * Number of

chromosome A chromosome is a package of DNA containing part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome-forming packaging proteins; in eukaryotic cells, the most import ...

s: 19 * Number of putative genes: 45,555, the largest number of genes ever recorded (estimate in September 2008) * Mitochondrial genome: 803,000 base pairs, 52

gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

s * Chloroplast genome: 157,000 base pairs, 101 genes

Somatic mosaicism

Genome-wide analysis of 11 clumps of ''P. trichocarpa'' trees reveals significant genetic differences between the roots and the leaves and branches of the same tree. The variation within a specimen is as much as found between unrelated trees. These results may be important in resolving debate in evolutionary biology regarding

somatic mutation A somatic mutation is a change in the DNA sequence of a somatic cell of a multicellular organism with dedicated reproductive cells; that is, any mutation that occurs in a cell other than a gamete, germ cell, or gametocyte. Unlike germline muta ...

(that evolution can occur within individuals, not solely among populations), with a variety of implications.