Salix × fragilis#Invasive species
{{Short description|Species of tree}}
{{Redirect|Crack willow|Eastern crack willow|Salix euxina}}
{{Speciesbox
|image = Salix fragilis 001.jpg
|image_caption = Leaves
|genus = Salix
|species = × fragilis
|authority = L.
|synonyms =
{{Species list
|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.
}}
}}
File:Salix fragilis 002.jpg, 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.Meikle, R. D. (1984). Willows and Poplars of Great Britain and Ireland. BSBI Handbook No. 4. {{ISBN|0-901158-07-0}}.Rushforth, K. (1999). Trees of Britain and Europe. Collins {{ISBN|0-00-220013-9}}.[http://www.na.fs.fed.us/fhp/invasive_plants/weeds/crack-willow.pdf USFS—United States Forest Service: Salix fragilis — "Weed of the Week"] . accessed 1.13.2013 It is a hybrid between Salix euxina and Salix alba, and is very variable, with forms linking both parents.
Description
Salix × fragilis is a medium-sized to large deciduous tree, which grows rapidly to {{convert|10|–|20|m|ft|abbr=on}} (rarely to {{convert|29|m|ft|abbr=on}}) tall, with a trunk up to {{convert|1|m|ft|abbr=on}} 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.
The flowers are produced in catkins in early spring, and 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 also 4–6 cm long, with the individual flowers having either one or two nectaries.Bean, W. J. (1980). Trees and Shrubs Hardy in the British Isles 8th ed., vol. 4. John Murray {{ISBN|0-7195-2428-8}}. In late spring fruit capsules release numerous small cotton-tufted seeds. They are easily distributed by wind and moving water, and germinate immediately after soil contact.
Taxonomy
Carl Linnaeus first described a willow species as "Salix fragilis" in 1753. It was later discovered that Linnaeus was actually describing a species he had also called Salix pentandra. At least since the 1920s, botanists applied Linnaeus's name "Salix fragilis" both to a pure species and to its hybrid with Salix alba. 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. After discussion, the decision was made by the Nomenclature Committee for Vascular Plants in 2009 to reject the first proposal and conserve "Salix fragilis" for the hybrid. Irina V. Belyaeva then described the previously unnamed parent species as Salix euxina, and designated a lectotype for the hybrid. The lectotype was shown by molecular evidence to be the hybrid between S. alba and S. euxina, the name of which is written as Salix × fragilis to show its hybrid status.
=Varieties=
S. × fragilis is very variable, with forms linking both parents. Some formally named varieties include the following. {{As of|2021|August}}, none were accepted at this rank by Plants of the World Online, being treated as synonyms of the species. Clive A. Stace suggested some would be better treated as cultivars.
- S. × fragilis var. decipiens W.D.J.Koch (S. × decipiens Hoffm.) – assigned to S. × fragilis by Plants of the World Online and by Belyaeva, but to S. euxina by Stace
- S. × fragilis var. furcata Ser. ex Gaudin – male tree with relatively wide leaves; of cultivated origin
- S. × fragilis var. fragilis – male and female trees known; leaves with even, well spaced teeth
- 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
Ecology
The plant is commonly called crack willow or brittle willow because it is highly susceptible to wind, ice and snow damage. 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 take root readily, enabling the species to colonise new areas as broken twigs fall into waterways and can be carried some distance downstream. It is particularly adept at colonising new riverside sandbanks formed after floods. It also spreads by root suckers, expanding into pure 'groves'.
Cultivation
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 {{convert|20|–|25|m|ft|abbr=on}} tall, with leaves up to 15 cm long. It is a female clone.
Invasive species
Salix × fragilis has escaped cultivation to become an invasive species in various parts of the world,[http://www.invasive.org/browse/subinfo.cfm?sub=11590 Invasive.org Salix fragilis (crack willow)] . accessed 1.13.2013 including: all states and territories in Australia,{{Cite web | url=https://keyserver.lucidcentral.org/weeds/data/media/Html/salix_fragilis.htm | title=Salix fragilis}} New Zealand; the upper half of the United States;,U.S. states with invasive S. × fragilis sites include: CN, CO, ID, IL, IN, IO, MA, MI, MN, MO, NB, ND, NJ, OH, OR, NH, NM, NV, NY, PA, RI, SD, UT, VA, VT, WA, WI, WV, and WY. (USFS & invasive.org) South Africa{{Cite web | url=http://www.capetowngreenmap.co.za/go-green/plant-indigenous-garden | title=Plant an indigenous garden}} and Brazil.{{Cite journal|title=Invasion by a non-native willow (Salix × rubens) in Brazilian subtropical highlands |date=2020|journal=Perspectives in Ecology and Conservation |issue=3 |last1=Sühs |first1=Rafael Barbizan |last2=Dechoum |first2=Michele de Sá |pages=203–209 |language=en |doi=10.1016/j.pecon.2020.09.001 |last3=Ziller |first3=Silvia Renate|volume=18 |doi-access=free }}{{Cite journal |last1=Zenni |first1=Rafael D. |last2=Ziller |first2=Sílvia R. |last3=da Rosa |first3=Clarissa A. |last4=Sühs |first4=Rafael B. |last5=Puechagut |first5=Patricia B. |last6=Marterer |first6=Beloni T. P. |last7=Heringer |first7=Gustavo |last8=de Matos |first8=Ana Carolina L. |last9=Bueno |first9=Marina L. |last10=Almeida |first10=Jonathan W. |last11=Silva |first11=Carlos H. T. |last12=Legracie-Júnior |first12=José Renato |last13=Chapla |first13=Tatiani E. |date=2024 |title=Invasive non-native species in Brazil: an updated overview |url=https://link.springer.com/10.1007/s10530-024-03302-9 |journal=Biological Invasions |language=en |volume=26 |issue=8 |pages=2397–2405 |doi=10.1007/s10530-024-03302-9 |issn=1387-3547|url-access=subscription }} 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.{{Cite journal|last1=Griffiths|first1=J|last2=Armstrong|first2=H|last3=Innes|first3=R|last4=Terry|first4=J|date=January 2018|title=Can aerial herbicide application control Grey Willow (Salix cinerea L.) and stimulate native plant recovery in New Zealand wetlands?|journal=Ecological Management & Restoration|volume=19|issue=1|pages=49–57|doi=10.1111/emr.12299|issn=1442-7001}} As only the male plant is present in New Zealand no fruit is formed unless hybridised.{{Cite web |url=http://www.biosecurity.govt.nz/pests/crack-willow |title=Crack willow | MPI Biosecurity New Zealand |access-date=2013-04-22 |archive-date=2016-04-14 |archive-url=https://web.archive.org/web/20160414115537/http://www.biosecurity.govt.nz/pests/crack-willow |url-status=dead }} Species spread is facilitated by stem fragmentation which are carried via waterways and nearby adult individuals.{{Cite journal |last1=Becker |first1=Laise Orsi |last2=Sühs |first2=Rafael Barbizan |last3=Dechoum |first3=Michele de Sá |date=2023-12-07 |title=Understanding willow invasion in subtropical highlands |url=https://link.springer.com/10.1007/s10530-023-03206-0 |journal=Biological Invasions |volume=26 |issue=3 |pages=769–778 |language=en |doi=10.1007/s10530-023-03206-0 |issn=1387-3547|url-access=subscription }} Control and management for habitat restoration projects often uses herbicides.{{Cite journal|last1=Griffiths|first1=James|last2=McAlpine|first2=Kate|date=2017|title=Aerial glyphosate application reduces grey willow (Salix cinerea) canopy cover, increases light availability, and stimulates kahikatea (Dacrycarpus dacrydioides) growth|journal=New Zealand Journal of Ecology|volume=41|issue=2|doi=10.20417/nzjecol.41.22|doi-access=free}}
References
{{Reflist|refs=
{{cite web |title=Salix × fragilis L. |work=The International Plant Names Index |url=https://www.ipni.org/n/777611-1 |access-date=2021-08-07 }}
{{citation |title=Salix euxina I.V.Belyaeva |work=The International Plant Names Index |url=http://www.ipni.org/ipni/idPlantNameSearch.do?id=77102927-1 |accessdate=2021-08-07}}
}}
External links
{{Commons category|Salix fragilis}}
{{Wikispecies|Salix fragilis}}
- [http://www.na.fs.fed.us/fhp/invasive_plants/weeds/crack-willow.pdf USFS—United States Forest Service: Salix fragilis — "Weed of the Week"]
- [http://www.invasive.org/browse/subinfo.cfm?sub=11590 Center for Invasive Species and Ecosystem Health—Invasive.org] — photos gallery.
- {{PFAF|Salix fragilis}}
{{Taxonbar|from=Q157518}}
{{DEFAULTSORT:Salix fragilis}}
Category:Flora of Western Asia
Category:Garden plants of Europe
Category:Plants described in 1753