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Populus is a genus of 25–30 species of deciduous flowering plants in the family Salicaceae, native to most of the Northern Hemisphere. English names variously applied to different species include poplar (), aspen, and cottonwood.
The western balsam poplar ( P. trichocarpa) was the first tree to have its full DNA code determined by DNA sequencing, in 2006.Joint Genome Institute, Populus trichocarpa
The bark on young trees is smooth and white to greenish or dark gray, and often has conspicuous ; on old trees, it remains smooth in some species, but becomes rough and deeply fissured in others. The shoots are stout, with (unlike in the related ) the terminal bud present. The leaves are spirally arranged, and vary in shape from triangular to circular or (rarely) lobed, and with a long petiole; in species in the sections Populus and Aigeiros, the petioles are laterally flattened, so that breezes easily cause the leaves to wobble back and forth, giving the whole tree a "twinkling" appearance in a breeze. Leaf size is very variable even on a single tree, typically with small leaves on side shoots, and very large leaves on strong-growing lead shoots. The leaves often turn bright gold to yellow before they fall during autumn.Meikle, R. D. (1984). Willows and Poplars of Great Britain and Ireland. BSBI Handbook No. 4. .Rushforth, K. (1999). Trees of Britain and rope. Collins .
The are mostly dioecious (rarely monoecious) and appear in early spring before the leaves. They are borne in long, drooping, sessile or pedunculate produced from buds formed in the axils of the leaves from the previous year. The flowers are each seated in a cup-shaped disk which is borne on the base of a scale which is itself attached to the rachis of the catkin. The scales are obovate, lobed, and fringed, membranous, hairy or smooth, and usually caducous. The male flowers are without calyx or corolla, and comprise a group of four to 60 inserted on a disk; filaments are short and pale yellow; are oblong, purple or red, introrse, and two-celled; the cells open longitudinally. The female flower also has no calyx or corolla, and comprises a single-celled ovary seated in a cup-shaped disk. The style is short, with two to four stigmata, variously lobed, and numerous ovules. Pollination is by wind, with the female catkins lengthening considerably between pollination and maturity. The fruit is a two- to four-valved dehiscent capsule, green to reddish-brown, mature in midsummer, containing numerous minute, light-brown surrounded by tufts of long, soft, white hairs aiding wind dispersal.
Poplars and aspens are important food plants for the of a large number of Lepidoptera species. Pleurotus populinus, the aspen oyster mushroom, is found exclusively on dead wood of Populus trees in North America.
Several species of Populus in the United Kingdom and other parts of Europe have experienced heavy Forest dieback; this is thought in part to be due to Hornet moth which bores into the trunk of the tree during its larval stage.
Trees with fastigiate (erect, columnar) branching are particularly popular, and are widely grown across Europe and southwest Asia. However, like , poplars have very vigorous and invasive root systems stretching up to from the trees; planting close to houses or ceramic water pipes may result in damaged foundations and cracked walls and pipes due to their search for moisture.
A simple, reproducible, high-frequency micropropagation protocol in eastern cottonwood Populus deltoides has been reported by Yadav et al. 2009.
The trees are grown from kalam or cuttings, harvested annually in January and February, and commercially available up to 15November.
Poplars are most commonly used to make plywood: Yamuna Nagar in Haryana state has a large plywood industry reliant upon poplar. It is graded according to sizes known as "over" (over ), "under" (), and "sokta" (less than ).
Its flexibility and close grain make it suitable for a number of applications, similar to those of willow. The Greeks and Etruscans made shields of poplar, and Pliny the Elder also recommended poplar for this purpose. Poplar continued to be used for shield construction through the Middle Ages and was renowned for a durability similar to that of oak, but with a substantial reduction in weight.
In the United Kingdom, poplar (as with fellow energy crop willow) is typically grown in a short rotation coppice system for two to five years (with single or multiple stems), then harvested and burned - the yield of some varieties can be as high as 12 oven-dry tonnes per hectare every year.
In warmer regions like Italy this crop can produce up to 13.8, 16.4 oven-dry tonnes of biomass per hectare every year for biannual and triennial cutting cycles also showing a positive energy balance and a high energy efficiency.
In Sweden and other parts of Europe, poplar plantations on agricultural land have demonstrated considerable potential for supplying biomass for energy, with studies showing high yields and positive energy balances. Research indicates that these plantations can be managed sustainably with appropriate practices. For instance, nitrogen fertilization has been shown to increase biomass yields, although its effects on nutrient leaching and environmental quality require careful management. Studies also highlight the importance of considering water and soil quality when establishing Populus plantations, as well-managed systems can have neutral or even positive impacts on groundwater and soil organic carbon.
Furthermore, poplar and willow plantations can provide ecosystem services beyond bioenergy, such as improving water quality and contributing to phytotechnologies for environmental remediation. Overall, the cultivation of Populus for energy use is viewed as a promising and sustainable approach in temperate regions, provided that best management practices are followed.
Some stringed instruments are made with one-piece poplar backs; made in this fashion are said to have a particularly resonant tone. Similarly, though typically it is considered to have a less attractive grain than the traditional sitka spruce, poplar is beginning to be targeted by some harp as a sustainable and even superior alternative for their sound boards: Rees Harps Website, "Harp Myth #8". in these cases another hardwood veneer is sometimes applied to the resonant poplar base both for cosmetic reasons, and supposedly to fine-tune the acoustic properties.
Taxonomy
The genus Populus has traditionally been divided into six sections on the basis of leaf and flower characters;Eckenwalder, J.E. (1996). 9780660165066, NRC Research Press, National Research Council of Canada. ISBN 9780660165066 this classification is followed below. Recent genetic studies have largely supported this, confirming some previously suspected reticulate evolution due to past hybridisation and introgression events between the groups. Some species (noted below) had differing relationships indicated by their nuclear DNA (paternally inherited) and chloroplast DNA sequences (maternally inherited), a clear indication of likely hybrid origin.Hamzeh, M., & Dayanandan, S. (2004). Phylogeny of Populus (Salicaceae) based on nucleotide sequences of chloroplast TRNT-TRNF region and nuclear rDNA. Amer. J. Bot. 91: 1398-1408. Available online Hybridisation continues to be common in the genus, with several hybrids between species in different sections known. There are currently 57 accepted species in the genus." Populus L.". Plants of the World Online, Kew Science. Accessed 8 September 2021. [3]
Phylogeny
Some of the most easily identifiable fossils of this genus belongs to Populus wilmattae, which come from the Danian of North America about 58 million years ago. (2025). 9789251071854, The Food and Agriculture Organization of the United Nations. . ISBN 9789251071854 However, fossils from the Cretaceous of this genus have been found in Tibet and Heilongjiang, China.
Selected species
Ecology
Poplars of the cottonwood section are often wetlands or riparian trees. The aspens are among the most important Boreal ecosystem broadleaf trees.
Cultivation
Many poplars are grown as , with numerous used. They have the advantage of growing to a very large size at a rapid pace. Almost all poplars take root readily from cuttings or where broken branches lie on the ground (they also often have remarkable suckering abilities, and can form huge colonies from a single original tree, such as the famous Pando forest made of thousands of Populus tremuloides clones).
India
In India, the poplar is grown commercially by farmers, mainly in the Punjab region. Common poplar varieties are:
Pakistan
In Pakistan, poplar is grown on a commercial level by farmers in Punjab, Sindh, and Khyber Pakhtunkhwa Provinces. However, all varieties are seriously susceptible to termite attack, causing significant losses to poplar every year. Logs of poplar are therefore also used as bait in termite traps for biocontrol of termites in crops.
Uses
Although the wood from Populus is known as poplar wood, a common high-quality hardwood "poplar" with a greenish colour is actually from an unrelated genus Liriodendron. Populus wood is a lighter, more porous material.
Food
In addition to the foliage and other parts of Populus species being consumed by animals, the starchy sap layer (underneath the outer bark) is edible to humans, both raw and cooked.
Manufacturing
Energy
Interest exists in using poplar as an energy crop for biomass, in energy forestry systems, particularly in light of its high energy-in to energy-out ratio, large carbon mitigation potential, and fast growth.
Fuel
Biofuel is another option for using poplar as bioenergy supply. In the United States, scientists studied converting short rotation coppice poplar into sugars for biofuel (e.g. ethanol) production.
Considering the relative cheap price, the process of making biofuel from SRC can be economically feasible, although the conversion yield from short rotation coppice (as juvenile crops) were lower than regular mature wood. Besides biochemical conversion, thermochemical conversion (e.g. fast pyrolysis) was also studied for making biofuel from short rotation coppice poplar and was found to have higher energy recovery than that from bioconversion.
Art
Poplar was the most common wood used in Italy for ; the Mona Lisa and most famous early Italian Renaissance paintings are on poplar. The wood is generally white, often with a slightly yellowish colour.
Land management
are frequently used as a windbreak around agricultural fields to protect against wind erosion.
Agriculture
Logs from the poplar provide a growing medium for shiitake mushrooms. Shiitake growth studies performed by RMIT
Phytoremediation
Poplar represents a suitable candidate for phytoremediation since it has the ability to remove and store harmful pollutants in its trunk while also removing air pollution. This plant has been successfully used to target many types of pollutants including trace element (TEs) in soil and
landfill leachate Polychlorinated Biphenyl (PCBs),Meggo RE, Schnoor JL. Cleaning Polychlorinated Biphenyl (PCB) Contaminated Garden Soil by Phytoremediation. Environmental sciences. 2013;1(1):33-52 Trichloroethylene (TCE), Polycyclic Aromatic Hydrocarbon (PAHs).
In Billie Holiday's "Strange Fruit", she sings "Black bodies swinging in the southern breeze/Strange fruit hanging from the poplar trees…".
The Odd Poplars Alley, in Iași, Romania, is one of the spots where Mihai Eminescu sought inspiration in his works (the poem "Down Where the Lonely Poplars Grow"). In 1973, the 15 white poplars still left (with age ranges between 233 and 371 years) were declared natural monuments.
In Ukraine, one of neighborhoods of Kyiv is named after Populus nigra as Osokorky, a local name.
In Greek mythology, the Heliades were turned into poplar trees by the gods when their brother, Phaethon, died after attempting to drive his father, Helios, his chariot across the sky.
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