Populus is a genus of 25–30 species ofdeciduous flowering plants in the familySalicaceae, native to most of theNorthern Hemisphere. English names variously applied to different species includepoplar (/ˈpɒplər/),aspen, andcottonwood.
The western balsam poplar (P. trichocarpa) was the first tree to have its full DNA code determined byDNA sequencing, in 2006.[4]
Thebark on young trees is smooth and white to greenish or dark grey, and often has conspicuouslenticels; 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 relatedwillows) the terminal bud present. Theleaves are spirally arranged, and vary in shape from triangular to circular or (rarely) lobed, and with a longpetiole; in species in the sectionsPopulus andAigeiros, 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.[5][6]
The seeds of the poplar tree are easily dispersed by the wind, due to the fine hairs surrounding them.
Theflowers are mostlydioecious (rarelymonoecious) and appear in early spring before the leaves. They are borne in long, drooping, sessile or pedunculatecatkins 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 withoutcalyx orcorolla, and comprise a group of four to 60stamens inserted on a disk; filaments are short and pale yellow;anthers 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. Thefruit is a two- to four-valveddehiscentcapsule, green to reddish-brown, mature in midsummer, containing numerous minute, light-brownseeds surrounded by tufts of long, soft, white hairs aiding wind dispersal.[5][7]
Black poplarPopulus nigra on a hill through spring (top left), summer, autumn, and winter, in Germany
The genusPopulus has traditionally been divided into six sections on the basis of leaf and flower characters;[6][8] this classification is followed below. Recent genetic studies have largely supported this, confirming some previously suspected reticulate evolution due to pasthybridisation and introgression events between the groups. Some species (noted below) had differing relationships indicated by theirnuclear DNA (paternally inherited) andchloroplast DNA sequences (maternally inherited), a clear indication of likely hybrid origin.[9] Hybridisation continues to be common in the genus, with several hybrids between species in different sections known.[5][10] There are currently 57 accepted species in the genus.[11]
Some of the most easily identifiable fossils of this genus belongs toPopulus wilmattae, which come from theLate Paleocene of North America about 58 million years ago.[12] However, fossils from the Cretaceous of this genus have been found in Tibet and Heilongjiang, China.[13]
Poplars of the cottonwood section are often wetlands orriparian trees. The aspens are among the most importantboreal broadleaf trees.[5]
Poplars and aspens are important food plants for thelarvae of a large number ofLepidoptera species.Pleurotus populinus, the aspen oyster mushroom, is found exclusively on dead wood ofPopulus trees in North America.
Several species ofPopulus in the United Kingdom and other parts of Europe have experienced heavydieback; this is thought in part to be due toSesia apiformis which bores into the trunk of the tree during its larval stage.[16]
Fastigiate black poplar cultivar of the Plantierensis group, in HungaryPoplars dominate the flora ofKhorog City Park,Gorno-Badakhshan,Tajikistan
Many poplars are grown asornamental trees, with numerouscultivars 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 famousPando forest made of thousands ofPopulus tremuloides clones).
Trees withfastigiate (erect, columnar) branching are particularly popular, and are widely grown across Europe and southwest Asia. However, likewillows, poplars have very vigorous and invasive root systems stretching up to 40 metres (130 ft) 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 cottonwoodPopulus deltoides has been reported by Yadav et al. 2009.[17]
In India, the poplar is grown commercially by farmers, mainly in thePunjab region. Common poplar varieties are:
G48 (grown in the plains of Punjab, Haryana, UP)
w22 (grown in mountainous regions, e.g., Himachal Pradesh, Pathankot, Jammu)
The trees are grown fromkalam or cuttings, harvested annually in January and February, and commercially available up to 15November.
Poplars are most commonly used to makeplywood:Yamuna Nagar inHaryana state has a large plywood industry reliant upon poplar. It is graded according to sizes known as "over" (over 24 inches (610 mm)), "under" (18–24 inches (460–610 mm)), and "sokta" (less than 18 inches (460 mm)).
In Pakistan, poplar is grown on a commercial level by farmers in Punjab, Sindh, andKhyber 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.
Although the wood fromPopulus is known as poplar wood, a common high-quality hardwood "poplar" with a greenish colour is actually from an unrelated genusLiriodendron.Populus wood is a lighter, more porous material.
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, andPliny the Elder also recommended poplar for this purpose.[18] 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 addition to the foliage and other parts ofPopulus species being consumed by animals, the starchy sap layer (underneath the outer bark) is edible to humans, both raw and cooked.[19]
Poplar wood is also widely used in thesnowboard industry for the snowboard core, because it has exceptional flexibility, and is sometimes used in the bodies ofelectric guitars anddrums.
Poplar wood, particularly when seasoned, makes a good hearth for abow drill.
Because of its hightannic acid content, the bark has been used in Europe for tanning leather.[7]
Interest exists in using poplar as anenergy crop forbiomass, inenergy forestry systems, particularly in light of its high energy-in to energy-out ratio, large carbon mitigation potential, and fast growth.
Rotor poplar and willow cuttings planter, planting a new nursery of poplar for biomass with short rotation
In the United Kingdom, poplar (as with fellow energy crop willow) is typically grown in ashort 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.[22]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 highenergy efficiency.[23][24]
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.[25] 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.[26] Studies also highlight the importance of considering water and soil quality when establishingPopulus plantations, as well-managed systems can have neutral or even positive impacts on groundwater and soil organic carbon.[27]
Furthermore, poplar and willow plantations can provide ecosystem services beyond bioenergy, such as improving water quality and contributing to phytotechnologies for environmental remediation.[28] Overall, the cultivation ofPopulus for energy use is viewed as a promising and sustainable approach in temperate regions, provided that best management practices are followed.
Biofuel is another option for using poplar as bioenergy supply. In the United States, scientists studied convertingshort rotation coppice poplar into sugars for biofuel (e.g. ethanol) production.[29]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 higherenergy recovery than that from bioconversion.[30]
Poplar was the most common wood used in Italy forpanel paintings; theMona Lisa and most famous earlyItalian Renaissance paintings are on poplar.[31] The wood is generally white, often with a slightly yellowish colour.
Somestringed instruments are made with one-piece poplar backs;violas made in this fashion are said[citation needed] to have a particularly resonant tone. Similarly, though typically it is considered to have a less attractive grain than the traditionalsitka spruce, poplar is beginning to be targeted by someharpluthiers as a sustainable and even superior alternative for theirsound boards:[32] 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.
InBillie Holiday's "Strange Fruit", she sings "Black bodies swinging in the southern breeze/Strange fruit hanging from the poplar trees…".
The Odd Poplars Alley, inIași, Romania, is one of the spots whereMihai 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.[41]
In Greek mythology, theHeliades were turned into poplar trees by the gods when their brother,Paethon, died after attempting to drive his father,Helios, his chariot across the sky.
^abcdMeikle, R. D. (1984).Willows and Poplars of Great Britain and Ireland. BSBI Handbook No. 4.ISBN0-901158-07-0.
^abRushforth, K. (1999).Trees of Britain and rope. CollinsISBN0-00-220013-9.
^abKeeler, H. L. (1900).Our Native Trees and How to Identify Them. New York: Charles Scribner's Sons. pp. 410–412.
^Eckenwalder, J.E. (1996)."Systematics and evolution ofPopulus". In R.F. Stettler; H.D. Bradshaw; P.E. Heilman; T.M. Hinckley (eds.).Biology ofPopulus and its implications for management and conservation. Ottawa: NRC Research Press, National Research Council of Canada.ISBN9780660165066.
^Hamzeh, M., & Dayanandan, S. (2004). Phylogeny ofPopulus (Salicaceae) based on nucleotide sequences of chloroplast TRNT-TRNF region and nuclear rDNA.Amer. J. Bot. 91: 1398-1408. AvailableonlineArchived 29 January 2008 at theWayback Machine
^Eckenwalder, J.E. (2001). "Key to species and main crosses". In D.I. Dickmann; J.G. Isebrands; J.E. Eckenwalder; J. Richardson (eds.).Poplar culture in North America. Ottawa: NRC Research Press. pp. 325–330.ISBN978-0-660-18145-5.
^"Populus L.".Plants of the World Online, Kew Science. Accessed 8 September 2021.[1]Archived 26 February 2023 at theWayback Machine
^ab<Vázquez-García, José & Muñiz-Castro, Miguel Angel & González, Rosa & Nieves-Hernández, Gregorio & Pulido, Maria & Hernández-Vera, Gerardo & Delgadillo, Osvaldo. (2019). "Populus primaveralepensis sp. nov. (Salicaceae, Malpighiales), a new species of white poplar from the Bosque La Primavera Biosphere Reserve in Western Mexico".European Journal of Taxonomy. 2019. 10.5852/ejt.2019.498.
^Martin-Garcia, J. "Patterns and monitoring of Sesia apiformis infestations in poplar plantations at different spatial scales".Journal of Applied Entomology.
^Nassi; Di Nasso, N.; Guidi, W.; Ragaglini, G.; Tozzini, C.; Bonari, E. (2010). "Biomass production and energy balance of a twelve-year-old short-rotation coppice poplar stand under different cutting cycles".Global Change Biology Bioenergy.2 (2):89–97.doi:10.1111/j.1757-1707.2010.01043.x.S2CID86414864.
^Dou, C; Chandler, D.; Resende, F.; Renata, R. (2017). "Fast pyrolysis of short rotation coppice poplar: an investigation in thermochemical conversion of a realistic feedstock for the biorefinery".Biotechnology for Biofuels.10 (1): 144.doi:10.1021/acssuschemeng.7b01000.
^Uzielli, Luca; Gril, Joseph; Cocchi, Linda; Colmars, Julien; Dionisi Vici, Paolo; Dureisseix, David; Goli, Giacomo; Jullien, Delphine; Marcon, Bertrand; Mazzanti, Paola; Remond, Romain (July 2011)."Experimental studies on the wooden support of the "Mona Lisa"".The Safeguard of Cultural Heritage. A Challenge from the Past for the Europe of Tomorrow. COST Strategic Workshop. The safeguard of cultural heritage : a challenge from the past for the Europe for the Europe of tomorrow. Florence, Italy: Firenze University Press: 367 p.doi:10.13140/2.1.1021.1525.
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