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Salix × fragilis
Salix × fragilis
Salix × fragilis
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Salix × fragilis
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Rosids
Order: Malpighiales
Family: Salicaceae
Genus: Salix
Species:
S. × fragilis
Binomial name
Salix × fragilis
Synonyms[1]
  • Oisodix × decipiens Raf.
  • Psatherips × fragilis (L.) Raf.
  • Salix alba var. elyensis Burtt Davy
  • Salix × chlorocarpa Schur
  • Salix × decipiens Hoffm.
  • Salix × excelsa Tausch ex W.D.J.Koch
  • Salix × excelsior Host
  • Salix × fragilior Host
  • Salix × fragilissima Host
  • Salix × fragillima Schur
  • Salix × gracilenta Tausch
  • Salix × lyonii J.Forbes
  • Salix × monspeliensis J.Forbes
  • Salix × montana J.Forbes
  • Salix × neotricha Goerz
  • Salix × palustris Host
  • Salix × pendula Ser.
  • Salix × persicifolia Schleich.
  • Salix × rubens Schrank
  • Salix × russelliana Sm.
  • Salix × sanguinea Tausch ex Opiz
  • Salix × viridis Fr.
  • Salix × wargiana Lej.
  • Vimen × russeliana (Sm.) Raf.
In riparian habitat, Hesse, Germany

Salix × fragilis, with the common names crack willow and brittle willow, is a hybrid species of willow native to Europe and Western Asia. It is native to riparian habitats, usually found growing beside rivers and streams, and in marshes and water meadow channels.[2][3][4] It is a hybrid between Salix euxina and Salix alba, and is very variable, with forms linking both parents.[5]

Description

[edit]

Salix × fragilis is a medium-sized to large deciduous tree, which grows rapidly to 10–20 m (33–66 ft) (rarely to 29 m (95 ft)) tall, with a trunk up to 1 m (3.3 ft) diameter, often multi-trunked, and an irregular, often leaning crown. The bark is dark grey-brown, coarsely fissured in older trees. The lanceolate leaves are bright green, 9–15 cm long and 1.5–3 cm wide, with a finely serrated margin; they are very finely hairy at first in spring, but soon become hairless.[4]

The flowers are produced in catkins in early spring and are pollinated by insects. They are dioecious, with male and female catkins on separate trees. The male catkins are 4–6 cm long, the female catkins are the same length. The individual flowers have either one or two nectaries.[2][3][6] In late spring, the fruit capsules release numerous small cotton-tufted seeds. These are easily distributed by wind and moving water and germinate immediately upon contact with the soil.[4]

Taxonomy

[edit]

Carl Linnaeus first described a willow species as "Salix fragilis" in 1753.[7] It was later discovered that he was actually describing a species that he had also called Salix pentandra. Since at least the 1920s, botanists have applied Linnaeus's name "Salix fragilis" to both a pure species and to its hybrid with Salix alba.[8][9][10] In 2005, it was proposed that "Salix fragilis" should be conserved for the pure species, with the hybrid called "Salix × rubens". The alternative was to conserve "Salix fragilis" for the hybrid, with the pure species requiring a new name.[10] Following a discussion, the Nomenclature Committee for Vascular Plants rejected the initial proposal in 2009 and opted to conserve the name "Salix fragilis" for the hybrid.[11] Irina V. Belyaeva subsequently described the previously unnamed parent species as Salix euxina,[8][9][12] and designated a lectotype for the hybrid.[8] The lectotype was shown by molecular evidence to be the hybrid between S. alba and S. euxina,[9] the name of which is written as Salix × fragilis to show its hybrid status.[1][9]

Varieties

[edit]

S. × fragilis is very variable, with forms linking both parents. Some formally named varieties include the following.[1][5] As of August 2021, none were accepted at this rank by Plants of the World Online, being treated as synonyms of the species.[1] Clive A. Stace suggested some would be better treated as cultivars.[5]

  • S. × fragilis var. decipiens W.D.J.Koch (S. × decipiens Hoffm.) – assigned to S. × fragilis by Plants of the World Online[1] and by Belyaeva,[8] but to S. euxina by Stace[5]
  • S. × fragilis var. furcata Ser. ex Gaudin – male tree with relatively wide leaves; of cultivated origin[5]
  • S. × fragilis var. fragilis – male and female trees known; leaves with even, well spaced teeth[5]
  • S. × fragilis var. glauca Spenn.
  • S. × fragilis var. polyandra Wimm.
  • S. × fragilis var. rubens (Schrank) P.D.Sell
  • S. × fragilis var. russelliana (Sm.) W.D.J.Koch – Bedford willow; female tree with long narrow leaves having somewhat uneven teeth; of cultivated origin[5]

Ecology

[edit]

The plant is commonly called crack willow or brittle willow because it is highly susceptible to damage from wind, ice and snow.[4] The name also derives from the twigs, which break off very easily and cleanly at the base with an audible crack. Broken twigs and branches can readily take root, enabling the species to colonise new areas when they fall into waterways and are carried some distance downstream. The plant is particularly adept at colonising new riverside sandbanks formed after floods. It also spreads by root suckers, forming pure 'groves'.[4]

Cultivation

[edit]

Salix × fragilis is cultivated as a fast-growing ornamental tree. The cultivar 'Russelliana' (syn. S. × fragilis var. russelliana) is by far the most common clone of crack willow in Great Britain and Ireland, very easily propagated by cuttings. It is a vigorous tree commonly reaching 20–25 m (66–82 ft) tall, with leaves up to 15 cm long. It is a female clone.[2]

Invasive species

[edit]

Salix × fragilis has escaped cultivation to become an invasive species in various parts of the world,[13] including: all states and territories in Australia,[14] New Zealand; the upper half of the United States;,[4][15] South Africa[16] and Brazil.[17][18] In New Zealand it is listed on the National Pest Plant Accord, which means it cannot be sold or distributed. It can replace a habitat's native plant species diversity by forming monospecific stands.[19] As only the male plant is present in New Zealand no fruit is formed unless hybridised.[20] Species spread is facilitated by stem fragmentation which are carried via waterways and nearby adult individuals.[21] Control and management for habitat restoration projects often uses herbicides.[4][19][22]

[edit]

References

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[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Salix × fragilis

View on Grokipedia
from Grokipedia
Salix × fragilis, commonly known as crack willow or brittle willow, is a hybrid deciduous tree in the willow family (Salicaceae), arising from the cross between Salix alba (white willow) and Salix euxina (brittle willow). It typically grows to 15–25 meters tall, featuring a broad, rounded crown with brittle branches that readily snap at the base, facilitating vegetative reproduction through root-sprouting from fragments. The alternate leaves are narrowly lanceolate to elliptic, 5–15 cm long, with finely serrated margins, bright green above and glaucous (pale blue-green) below; male and female catkins appear in spring before the leaves, with the tree being dioecious. Native to Eurasia, particularly riverine habitats in Europe and western Asia, it is widely cultivated and naturalized globally for its rapid growth and utility in erosion control. Taxonomically, S. × fragilis belongs to section Salix of the Salix, which comprises over 400 of mostly riparian trees and shrubs. The hybrid origin leads to variability, with fertile capable of back-crossing to parent , forming hybrid swarms; numbers vary (e.g., 2n = 57–76), reflecting its allopolyploid nature. has been contentious, with some authorities treating S. × fragilis as the hybrid S. alba × S. euxina (where S. euxina was previously separated from S. fragilis), while others, including recent studies, recommend S. × rubens for the S. alba × S. fragilis hybrid and retain S. fragilis as a distinct to distinguish it from the hybrid. Despite this, S. × fragilis remains the commonly accepted name for the widespread hybrid in and . Ecologically, S. × fragilis thrives in moist, disturbed soils along streams, lakeshores, wetlands, and floodplains, tolerating periodic flooding and poor drainage but preferring full sun. It exhibits high phenotypic plasticity, growing rapidly (up to 1–2 m per year) and forming dense thickets that stabilize banks with extensive fibrous roots, though this can lead to infrastructure damage. As an introduced species in North America, it is often invasive, outcompeting native vegetation due to prolific vegetative propagation—rarely producing viable seeds—and altering hydrology; it is listed as a weed in several U.S. states, with management focusing on removal to prevent spread. Pollinators such as bees visit its early-season catkins, and it serves as a larval host for certain butterflies. Human uses of S. × fragilis include ornamental planting, production via , and traditional applications such as basketry from flexible twigs, timber for light construction, and medicinal extracts from bark containing (a precursor to aspirin) for pain relief and purposes. Its tannin-rich bark (5–12% content) has been used for and leather tanning, while the tree's saccharine exudates provide minor value. However, due to its invasiveness and aggressive rooting, it is not recommended for new plantings in sensitive ecosystems, with sterile cultivars preferred where cultivation is desired.

Taxonomy

Nomenclature and etymology

The binomial name Salix fragilis was established by in his seminal work in 1753, where it was described as a distinct willow species characterized by its fragile branches. Subsequent taxonomic revisions have clarified its hybrid origin, leading to the current designation Salix × fragilis, denoting the nothospecies resulting from the cross between Salix alba L. (white willow) and Salix euxina I.V. Belyaeva. Common names for Salix × fragilis include crack willow and brittle willow in English, reflecting the plant's tendency for branches to snap easily at the base, facilitating vegetative propagation. In German, it is known as Bruch-Weide or Knack-Weide, emphasizing the same brittle quality. The etymology of the name traces to Latin roots: the genus Salix directly from the classical Latin term for willow, used since antiquity to denote trees of this group. The specific epithet fragilis derives from Latin fragilis, meaning brittle or fragile, alluding to the twigs that readily detach and break. Historically, the name Salix fragilis has been subject to misapplications and synonyms, including treatment as Salix alba L. var. fragilis (Pend.) W.D.J. Koch, which conflated it with the parent species S. alba. Another synonym is Salix × rubens Schrank, once used for the same hybrid combination before taxonomic stabilization. These nomenclatural adjustments stem from improved understanding of willow hybridization patterns in the genus Salix.

Classification and hybrids

Salix × fragilis is placed in the family (willows and poplars), order , in the Salix, which encompasses approximately 400 species of primarily trees and shrubs adapted to riparian and habitats worldwide. Within the , it belongs to subgenus Salix and section Salix, a group characterized by tall, fast-growing trees with lanceolate leaves and catkins borne on separate male and female plants. The taxon originates as a natural hybrid between Salix alba L. (white willow), widely distributed across Europe and parts of , and Salix euxina I.V.Belyaeva, a endemic to eastern and western . Originally described as a distinct by in 1753, its hybrid nature was clarified in modern through detailed morphological and genetic analyses, with Belyaeva's 2009 revision distinguishing S. euxina as the maternal parent and reassigning the name S. × fragilis to the hybrid. This parentage explains its intermediate traits, such as brittle branches and variable leaf pubescence, which bridge the characteristics of its progenitors. However, this revision remains debated; a 2022 study by Marchenko and Kuzovkina challenges the validity of S. euxina, proposing instead to retain S. fragilis as the and recognize S. × rubens as the hybrid S. alba × S. fragilis. Taxonomic challenges persist due to extensive hybridization within section Salix and morphological overlap with S. alba, often resulting in misidentifications in herbaria and field surveys. Different regional floras treat it variably: some maintain it as a species (S. fragilis L.), while others, including the Euro+Med Plantbase, recognize it strictly as a hybrid (S. × fragilis L.). These inconsistencies highlight the need for integrated molecular approaches to resolve , as and frequent complicate delimitation. As a fertile hybrid, Salix × fragilis contributes to hybrid swarms through with parental species, underscoring the reticulate evolution prevalent in the , where it acts as both a and intermediary in diversification.

Varieties

Salix × fragilis encompasses a number of infraspecific taxa and selected cultivars, primarily differentiated by stem characteristics, morphology, and ornamental qualities. The variety S. × fragilis var. furcata is distinguished by its forked catkins and brittle, glossy brown shoots that readily snap at the base, a trait contributing to vegetative . This vigorous tree produces lance-shaped leaves that are coarsely serrated, glossy dark green above, and beneath, with slender catkins emerging in early spring. S. × fragilis var. basfordiana, often treated as a narrow-leaved form or nothovariety, features long, narrow, bright green leaves up to 15 cm long and 1.5–2 cm wide, finely serrated and glabrous, paired with polished orange-yellow branchlets. As a clone, it bears drooping catkins 6–10 cm long in April, enhancing its appeal for landscape use. Popular cultivars include 'Aurea', a selection of the form f. vitellina valued for its golden-yellow foliage and vivid yellow winter stems, providing striking ornamental contrast in damp sites. This cultivar exhibits chartreuse leaves during the , supporting its selection for aesthetic purposes in . The infraspecific of S. × fragilis remains debated, particularly concerning the stability of varieties versus their emergence through with parental species like S. alba. Such contributes to morphological variability in the hybrid complex, with ovule number identified as a reliable diagnostic trait; Argus (1986) emphasized this in willow , while recent studies affirm ongoing hybridization as a driver of form diversity.

Description

Morphology

Salix × fragilis is a or large that typically grows to 10–20 meters in height, occasionally reaching up to 30 meters, with a trunk diameter of up to 1 meter. It exhibits a broad, rounded crown and often features a low-branching , with the trunk frequently dividing into several large stems near the base, contributing to its characteristic sprawling form. The branches are notably brittle at their bases, a trait that facilitates vegetative propagation but also makes the tree prone to breakage during storms. The bark on mature is gray to gray-brown, becoming deeply fissured with irregular ridges and furrows as the ages. On younger stems, the bark is smoother and more uniform in color. Twigs are slender, initially pubescent and tan or yellowish, turning to yellowish-brown with age; they are covered in silky hairs when young and often display a bright hue in winter, especially on vigorous shoots. Leaves are alternate, simple, and lanceolate to narrowly elliptic, measuring 5–15 cm in length and 1–3 cm in width, with finely serrate or serrulate margins. The adaxial surface is dark green and slightly glossy to dull, while the abaxial surface is and pale blue-green; young leaves are densely silky-pubescent but become sparsely hairy to glabrescent with maturity. Petioles are short, 0.8–1.2 cm long, and often bear small glands. The is dioecious, producing separate and female flowers in catkins that emerge in spring, typically before the leaves fully expand. Male catkins are 4–6 cm long, cylindrical, and yellowish due to the presence of two stamens with yellow anthers per flower. Female catkins are slightly shorter at 3–5 cm, greenish, with slender styles and ovaries that are pyriform and glabrous. Floral bracts are deciduous post-anthesis. Fruits consist of dehiscent capsules, 4–8 mm long, borne on the female catkins; each capsule contains 6–12 ovules that develop into numerous small seeds enveloped in cottony hairs, aiding wind dispersal. The capsules are glabrous and feature short styles (0.4–1 mm).

Growth and reproduction

_Salix × fragilis is a fast-growing deciduous tree, capable of rapid height increases in its early years, often reaching up to 1 meter per year under favorable moist conditions. This vigorous growth contributes to its role in short-rotation forestry and riparian stabilization, though individual trees typically have a relatively short lifespan of 50 to 100 years compared to longer-lived hardwoods. The species exhibits strong vegetative reproduction, primarily through root suckers and fragmentation of brittle branches, which readily root in moist soil or water, facilitating rapid clonal spread along waterways. As a dioecious species, separate male and female trees are required for sexual reproduction, but vegetative propagation often predominates in established populations. Sexual reproduction in S. × fragilis involves insect pollination of catkins, with male and female inflorescences appearing in early spring, typically from to May in its native European range. , produced in capsules, are covered in cottony hairs that aid dispersal, though along streams is also significant; however, seed viability is extremely short, often lasting only a few days to two weeks, necessitating immediate on suitable substrates. As a hybrid species derived from Salix alba and S. euxina, it displays hybrid vigor in growth but produces variable through sexual means, with many populations showing reduced and relying more on asexual methods. Phenologically, S. × fragilis leafs out early in spring, often before many other trees, with catkins emerging alongside or just after the leaves. In autumn, the lanceolate leaves turn a characteristic yellow before abscising, marking the end of the . This cycle supports its pioneer role in dynamic environments, where quick establishment via cuttings or suckers allows colonization of disturbed sites.

Distribution and habitat

Native range

Salix × fragilis is native to much of , ranging from the and in the west to in the east, and extending southward to the , , and the . Its distribution also includes western , encompassing the region, , and parts of southwestern Asia. However, taxonomic treatments vary, with some sources limiting nativity to Turkey and considering broader European occurrences as naturalized. The species is primarily associated with riparian zones, thriving in river valleys, floodplains, and along watercourses where periodic flooding occurs. This hybrid occupies temperate climates characterized by cold winters, tolerating minimum temperatures down to -30°C or lower in colder parts of its range, and warm summers where averages reach 20-25°C. Annual in its native habitats typically ranges from 500 to 1000 mm, supporting the moist conditions essential for its growth, though it can tolerate variations associated with continental influences in and . These climatic parameters align with USDA hardiness zones 4 to 8, reflecting its adaptation to seasonal extremes in Eurasian lowlands. In terms of site preferences, S. × fragilis favors alluvial and loamy soils that are rich in nutrients and retain moisture, with a pH range of 5.5 to 7.5, encompassing mildly acidic to neutral conditions. It is commonly found on floodplains, lake margins, and wetland edges, where well-drained yet consistently wet substrates prevail, often in association with other riparian vegetation. The species avoids shaded or dry uplands, confining its natural stands to dynamic aquatic-terrestrial interfaces. Historical records indicate that S. × fragilis was first collected and documented in the , with early botanical descriptions appearing around in Linnaeus's Species Plantarum, though precise hybrid identification solidified later. Stable populations have persisted in Eurasian riparian zones for centuries, contributing to its widespread natural occurrence prior to any cultivation or introduction elsewhere.

Introduced ranges

Salix × fragilis was introduced to during the , primarily for along waterways and as an ornamental . It reached and in the 19th century, with records indicating establishment in by 1880, again for stabilizing riverbanks and purposes. Introductions to southern and southern occurred in the 19th and early 20th centuries, often through colonial horticultural trade and intentional plantings in riparian zones. Today, S. × fragilis is widespread in the , the , and across much of , where it has naturalized extensively in temperate regions. In the , it occurs in southern , including and , as well as in southern , such as the Cape Provinces, Free State, , and . The species is largely absent from tropical areas, as it prefers temperate climates and is not well-suited to consistently warm, non-seasonal environments. Dispersal beyond its native European range has occurred mainly through human-mediated pathways, including deliberate plantings for , basketry, and , alongside accidental via contaminated or trade. Once established, it spreads naturally along waterways, facilitated by its brittle branches that break easily and root readily upon contact with moist . Establishment in introduced areas is supported by the ' adaptation to riparian and habitats similar to those in its native range, allowing it to thrive in disturbed, moist sites with full sun exposure. Its rapid from stem fragments enables frequent escapes from cultivation, contributing to broad in suitable temperate ecosystems.

Ecology

Interactions with other species

Salix × fragilis flowers are primarily pollinated by , including bees and flies, which are attracted to the and produced by its catkins in early spring. These pollinators play a crucial role in the plant's , as the exhibits dioecious characteristics with separate trees. Seed dispersal occurs mainly through wind, facilitated by the lightweight, cottony seeds released from female catkins, allowing for efficient colonization of nearby suitable habitats. The species provides significant and food resources for various . Birds utilize its branches for nesting and roosting. Mammals such as deer and browse on its twigs and foliage, particularly in riparian zones where it is abundant. Additionally, Salix × fragilis supports invertebrate communities, including numerous species that feed on its leaves and stems, serving as a base for food webs. Salix × fragilis forms symbiotic relationships with soil microorganisms to enhance nutrient uptake. Its roots associate with ectomycorrhizal and arbuscular mycorrhizal fungi, which improve phosphorus and other nutrient acquisition in nutrient-poor soils. Furthermore, endophytic diazotrophs colonize its root systems and contribute to atmospheric nitrogen fixation, benefiting the plant's growth in nitrogen-limited environments. In ecological communities, Salix × fragilis acts as a strong competitor, particularly in disturbed riparian sites. Its rapid via root sprouting enables quick colonization, often outcompeting slower-growing for light and space in flood-prone or cleared areas. This facilitates its dominance in early successional stages, altering local composition. In non-native ranges, this can lead to reduced by displacing native riparian vegetation.

Environmental impacts

Salix × fragilis, commonly known as crack willow, plays a significant role in stabilizing riparian environments through its extensive . The fibrous penetrate deeply into , anchoring the substrate and preventing along riverbanks and edges, particularly during high-flow events such as floods. This binding action reduces mobilization and downstream deposition, maintaining channel morphology and . Studies have demonstrated that the root reinforcement provided by S. × fragilis can increase stream bank stability by enhancing , with root density contributing up to a improvement in geotechnical models. In terms of water quality improvement, S. × fragilis exhibits strong capabilities, absorbing like and from contaminated sediments and water. This uptake occurs primarily through absorption and translocation to aboveground , which can then be harvested to remove contaminants from the . Field trials have shown that S. × fragilis accumulates significant metal concentrations in their tissues, making them suitable for remediating polluted riparian zones. Additionally, the plant's helps filter pollutants, reducing leaching into . The canopy of S. × fragilis influences local microclimates by providing shade that lowers stream temperatures, which benefits temperature-sensitive aquatic organisms such as and . Dense foliage can reduce water temperatures by several degrees , mitigating in warming climates. Regarding , the rapid biomass accumulation of S. × fragilis in short-rotation plantations enables substantial CO₂ absorption, with estimates around 25 tons of CO₂ per hectare per year depending on site conditions and management. This high growth rate, supported by efficient nutrient cycling and practices, positions the species as a valuable contributor to mitigating atmospheric carbon levels in riparian systems.

Cultivation and uses

Horticultural cultivation

Salix × fragilis is primarily propagated vegetatively through stem cuttings, a method that is very easy and reliable, with mature wood cuttings taken from November to February rooting readily when inserted into a sheltered bed or directly into their permanent position. Half-ripe wood cuttings from June to August can also be used in a frame for propagation. Seed sowing is less common, as the hybrid nature often results in reduced fertility, though viable seeds can be surface-sown in late spring immediately after ripening due to their short viability of just a few days. For optimal growth in horticultural settings, plant Salix × fragilis in full sun with deep, moderately fertile, moist to wet soil, tolerating heavy clay and intermittently flooded conditions but avoiding chalky or dry sites. Space trees 3-5 meters apart to accommodate their fast growth and broad canopy, and avoid planting near buildings or structures due to the risk of root damage and branch breakage from their brittle wood. The species is hardy to USDA zone 4, withstanding cold down to -34°C, making it suitable for temperate landscapes. Maintenance involves regular pruning in late winter or early spring (pruning groups 1 or 7) to manage the plant's inherent and encourage vigorous new growth, particularly if coppiced for form. Monitor for common pests such as , caterpillars, mites, beetles, larvae, and willow scale, which can be controlled through cultural practices or targeted treatments. The tree's aggressive roots may require attention in garden settings to prevent interference with drainage systems. Ornamentally, Salix × fragilis is valued for creating screens and hedges due to its rapid growth and dense foliage, with cultivars like 'Basfordiana' selected for golden-yellow winter stems and 'Bullata' for compact form and ornamental appeal in smaller landscapes.

Commercial and medicinal uses

Salix × fragilis is cultivated as a crop for production, with fast-growing hybrids achieving yields of up to 20 tonnes of per per year in short-rotation coppice systems. The wood serves as timber for constructing crates, poles, carts, and floors, reaching usable maturity by 15-20 years in suitable climates. Young, flexible shoots are harvested for basketry and coarse wickerwork, a traditional application in rural economies. During the 20th century, willows including S. × fragilis were planted extensively in parts of , such as in the UK, as part of multifunctional rural landscapes, contributing to wood production for , , and other utilitarian purposes. The bark of S. × fragilis contains , a that serves as a precursor to and exhibits and properties. Historically, it has been used to alleviate pain from , , , , and headaches, as well as to reduce fevers and treat with leaf preparations. In modern , bark extracts are incorporated into remedies for , muscle pain, and conditions like ; willow bark (primarily from species such as Salix alba) provided the traditional basis for the development of aspirin. Beyond these applications, S. × fragilis aids in engineering projects for , where it is planted along riverbanks, embankments, and sand dunes to stabilize . It also shows potential in , accumulating from contaminated soils while producing . The inner bark and young shoots provide for such as , sheep, and goats when fed in moderation as a supplementary feed.

Invasiveness

Invasive status

Salix × fragilis is designated as invasive in multiple introduced regions, including Midwest wetlands (such as in states like , , and ), riparian zones in , and various parts of , notably . In Australia, it is classified as one of the worst environmental weeds and a weed of national significance. The primary invasion pathways involve escape from ornamental and erosion-control plantings, with playing a key role; brittle branches break easily, and fragments float downstream in watercourses, readily rooting to establish new populations. This mode of spread facilitates rapid colonization of waterways, often leading to dense infestations far from original sites. In invaded areas, S. × fragilis forms dense monocultures that outcompete native vegetation, significantly reducing by shading out plants and altering habitat structure. It also impacts through high rates that increase loss and , potentially lowering stream flows, while root systems and fallen debris can impede water movement, exacerbate flooding, and promote . Legally, S. × fragilis is restricted in several jurisdictions; it is declared an unwanted organism in , prohibiting sale, propagation, or distribution, and is banned from sale or exchange in Australian states like under laws. In the United States, while not federally noxious, it is managed as an in affected states through local regulations.

Control and management

Preventing the establishment and spread of Salix × fragilis is crucial in areas where it poses an invasive , particularly along riparian zones. Land managers are advised to avoid planting this or its hybrids near waterways to minimize downstream dispersal via vegetative fragments. Instead, sterile hybrids or non-invasive cultivars, such as certain pussy willows, should be selected for any horticultural needs to reduce the risk of unintended propagation. Early detection through regular monitoring of watercourses can enable prompt intervention before populations expand. Mechanical control methods focus on physical removal to disrupt the plant's vegetative reproduction, which occurs readily from detached stems. Small saplings can be hand-pulled or dug out, while larger trees are cut at or just above ground level, followed by complete stump excavation to prevent resprouting. For dense stands, repeated mowing or cutting over multiple seasons exhausts root reserves and limits regrowth, though this approach requires consistent follow-up to be effective. These techniques are most successful in dry conditions and when combined with other methods, as cut material must be disposed of away from water to avoid further spread. Chemical control targets the plant's ability to regenerate from stumps and is often applied after mechanical cutting for higher efficacy. Herbicides such as are recommended for cut-stump treatments, where the chemical is painted or sprayed directly onto fresh cuts to translocate to roots. Application in late summer or autumn maximizes uptake and minimizes off-target effects on aquatic life, using formulations approved for near-water use like . Stem injection or basal bark spraying provides alternatives for larger specimens, ensuring targeted delivery while protecting surrounding vegetation. Biological control options remain underdeveloped but show promise for long-term suppression, leveraging natural enemies from the ' native range. fungi in the genus Melampsora spp. have been identified as potential agents that weaken growth by causing leaf damage and reducing vigor. Insect herbivores, such as leaf-feeding beetles and gall midges specific to Salix, are under evaluation for classical biological control programs, particularly in regions like where no native willows exist to risk non-target impacts. approaches combine these with mechanical and chemical methods, incorporating grazing by livestock to check establishment and periodic burning to reduce . Following eradication efforts, restoration enhances recovery by reestablishing native plant communities that outcompete residual S. × fragilis propagules. Sites should be replanted with indigenous riparian species, such as sedges, rushes, and native trees, to stabilize banks and restore . Ongoing monitoring for at least two to three years post-removal ensures any resprouts are addressed, promoting long-term resilience.

References

  1. https://www.minnesotawildflowers.info/tree/crack-willow
  2. https://fieldguide.mt.gov/speciesDetail.aspx?elcode=PDSAL024I0
  3. https://floranorthamerica.org/Salix_%C3%97fragilis
  4. https://onlinelibrary.wiley.com/doi/full/10.1002/tax.12685
  5. https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:777611-1
  6. https://www.cabidigitallibrary.org/doi/full/10.1079/cabicompendium.48577
  7. https://europlusmed.org/cdm_dataportal/taxon/168b4a20-5848-497d-991c-cc222dc71c3a
  8. https://www.rhs.org.uk/plants/239902/salix-fragilis-var-furcata/details
  9. https://www.treesandshrubsonline.org/articles/salix/salix-fragilis/
  10. https://olddairynursery.com/products/salix-fragilis-f-vitellina-aurea
  11. https://extension.usu.edu/forestry/tree-identification/willows/crack-willow
  12. https://harrodsoutdoor.com/product/crack-willow-hedging-salix-fragilis/
  13. https://elsoms.com/en/rest-of-world/trees/broadleaf-species/crack-willow-salix-fragilis
  14. https://www.fs.usda.gov/nsl/Wpsm/Salix.pdf
  15. https://pfaf.org/user/Plant.aspx?LatinName=Salix+fragilis
  16. https://www.woodlandtrust.org.uk/trees-woods-and-wildlife/british-trees/a-z-of-british-trees/crack-willow/
  17. https://www.worldfloraonline.org/taxon/wfo-0000928470
  18. https://pfaf.org/user/Plant.aspx?LatinName=Salix%20fragilis
  19. https://www.vdberk.com/trees/salix-fragilis/
  20. https://www.britannica.com/place/Germany/Climate
  21. http://www.misin.msu.edu/facts/detail/?project=&id=77
  22. https://tree.oplin.org/tree/willowcrack
  23. https://www.mdpi.com/1999-4907/14/5/959
  24. https://www.invasive.org/weedcd/pdfs/wow/crack-willow.pdf
  25. https://influentialpoints.com/Gallery/Aphids_on_willow_Salix.htm
  26. https://www.researchgate.net/publication/270967642_Testing_the_co-invasion_hypothesis_Ectomycorrhizal_fungal_communities_on_Alnus_glutinosa_and_Salix_fragilis_in_New_Zealand
  27. https://rngr.net/publications/tpn/54-2/evidence-for-nitrogen-fixation-in-the-salicaceae-family/at_download/file
  28. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/salix-fragilis
  29. https://www.researchgate.net/publication/370031109_Effect_of_riparian_invasion_by_the_crack_willow_Salix_fragilis_on_ecosystem_metabolism_in_North_Patagonian_streams
  30. https://www.researchgate.net/publication/396681385_Contribution_of_Salix_Fragilis_L_Roots_to_Stream_Bank_Stability
  31. https://www.mdpi.com/1999-4907/15/3/562
  32. https://nas.er.usgs.gov/queries/greatlakes/FactSheet.aspx?SpeciesID=2684&Potential=N&Type=0&HUCNumber=All%2520Great%2520Lakes
  33. https://www.sciencedirect.com/science/article/pii/S0301479721009336
  34. https://www.mdpi.com/2076-3417/10/22/8011
  35. https://practicalplants.org/wiki/salix_fragilis/
  36. https://www.shootgardening.com/plants/salix-x-fragilis
  37. https://greg.app/plant-care/salix-fragilis-var-bullata-crack-willow
  38. https://www.rhs.org.uk/plants/16249/salix-fragilis/details
  39. https://ornamentalgrass.ca/salix-fragilis-bullata.htm
  40. https://research.bangor.ac.uk/files/50100159/INDCRO_D_22_04197_final_version_30.9.22.pdf
  41. https://temperate.theferns.info/plant/Salix+%C3%97+fragilis
  42. https://link.springer.com/article/10.1007/s10531-021-02324-2
  43. https://www.frontiersin.org/journals/pharmacology/articles/10.3389/fphar.2021.593856/full
  44. https://www.mdpi.com/2076-3298/11/3/44
  45. https://www.ecan.govt.nz/pest-search/crack-willow-2
  46. https://weeds.dpi.nsw.gov.au/Weeds/Willows
  47. https://weeds.org.au/profiles/willows-except-weeping/
  48. https://nas.er.usgs.gov/queries/greatlakes/FactSheet.aspx?SpeciesID=2684
  49. https://riversofcarbon.org.au/resources/willows-willow-management/
  50. https://www.sgln.net.au/wp-content/uploads/2017/03/salix.pdf
  51. https://pesthub.es.govt.nz/?pwsystem=true&pwid=616&sort=alpha
  52. https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1440-6055.2006.00548.x
  53. https://www.capitolregionwd.org/projects/willow-reserve-restoration/
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