Salix × Fragilis
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''Salix'' × ''fragilis'', with the common names crack willow and brittle willow, is a hybrid species of
willow Willows, also called sallows and osiers, of the genus ''Salix'', comprise around 350 species (plus numerous hybrids) of typically deciduous trees and shrubs, found primarily on moist soils in cold and temperate regions. Most species are known ...
native to
Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...
and
Western Asia West Asia (also called Western Asia or Southwest Asia) is the westernmost region of Asia. As defined by most academics, UN bodies and other institutions, the subregion consists of Anatolia, the Arabian Peninsula, Iran, Mesopotamia, the Armenian ...
. It is native to riparian habitats, usually found growing beside rivers and
stream A stream is a continuous body of water, body of surface water Current (stream), flowing within the stream bed, bed and bank (geography), banks of a channel (geography), channel. Depending on its location or certain characteristics, a strea ...
s, and in
marsh In ecology, a marsh is a wetland that is dominated by herbaceous plants rather than by woody plants.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p More in genera ...
es and water meadow channels.Meikle, R. D. (1984). ''Willows and Poplars of Great Britain and Ireland''. BSBI Handbook No. 4. .Rushforth, K. (1999). ''Trees of Britain and Europe''. Collins .USFS—United States Forest Service: ''Salix fragilis'' — "Weed of the Week"
. accessed 1.13.2013
It is a hybrid between ''
Salix euxina ''Salix euxina'', the eastern crack-willow, is a species of flowering plant in the willow family Salicaceae, native from Turkey to the Caucasus. It was first described by I. V. Belyaeva in 2009. It is one of the parents of the common crack-willo ...
'' and ''
Salix alba ''Salix alba'', the white willow, is a species of willow native to Europe and western and Central Asia.Meikle, R. D. (1984). ''Willows and Poplars of Great Britain and Ireland''. BSBI Handbook No. 4. .Rushforth, K. (1999). ''Trees of Britain an ...
'', and is very variable, with forms linking both parents.


Description

''Salix'' × ''fragilis'' is a medium-sized to large
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 ...
tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, e.g., including only woody plants with secondary growth, only ...
, which grows rapidly to (rarely to ) tall, with a trunk up to diameter, often multi-trunked, and an irregular, often leaning crown. 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 dark grey-brown, coarsely fissured in older trees. The
lanceolate The following terms are used to describe leaf plant morphology, morphology in the description and taxonomy (biology), taxonomy of plants. Leaves may be simple (that is, the leaf blade or 'lamina' is undivided) or compound (that is, the leaf blade ...
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 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
flower 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 ...
s are produced in
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 in early spring, and pollinated by
insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...
s. They are
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 ...
, 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
nectar Nectar is a viscous, sugar-rich liquid produced by Plant, plants in glands called nectaries, either within the flowers with which it attracts pollination, pollinating animals, or by extrafloral nectaries, which provide a nutrient source to an ...
ies.Bean, W. J. (1980). ''Trees and Shrubs Hardy in the British Isles'' 8th ed., vol. 4. John Murray . 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 Carl Linnaeus (23 May 1707 – 10 January 1778), also known after ennoblement in 1761 as Carl von Linné,#Blunt, Blunt (2004), p. 171. was a Swedish biologist and physician who formalised binomial nomenclature, the modern system of naming o ...
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 ''Salix alba'', the white willow, is a species of willow native to Europe and western and Central Asia.Meikle, R. D. (1984). ''Willows and Poplars of Great Britain and Ireland''. BSBI Handbook No. 4. .Rushforth, K. (1999). ''Trees of Britain an ...
''. 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 ''Salix euxina'', the eastern crack-willow, is a species of flowering plant in the willow family Salicaceae, native from Turkey to the Caucasus. It was first described by I. V. Belyaeva in 2009. It is one of the parents of the common crack-willo ...
'', and designated a
lectotype In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to anchor or centralizes ...
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. , none were accepted at this rank by
Plants of the World Online Plants of the World Online (POWO) is an online taxonomic database published by the Royal Botanic Gardens, Kew. History Following the Convention on Biological Diversity, the Royal Botanic Gardens in Kew launched Plants of the World Online i ...
, 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
twig A twig is a thin, often short, branch of a tree or Bush (plant), bush. The buds on the twig are an important diagnostic characteristic, as are the abscission scars where the leaves have fallen away. The color, texture, and patterning of the t ...
s 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
flood A flood is an overflow of water (list of non-water floods, or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are of significant con ...
s. It also spreads by root suckers, expanding into pure 'groves'.


Cultivation

''Salix'' × ''fragilis'' is cultivated as a fast-growing
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 ...
. The
cultivar A cultivar is a kind of Horticulture, cultivated plant that people have selected for desired phenotypic trait, traits and which retains those traits when Plant propagation, propagated. Methods used to propagate cultivars include division, root a ...
'Russelliana' (syn. ''S.'' × ''fragilis'' var. ''russelliana'') is by far the most common clone of crack willow in
Great Britain Great Britain is an island in the North Atlantic Ocean off the north-west coast of continental Europe, consisting of the countries England, Scotland, and Wales. With an area of , it is the largest of the British Isles, the List of European ...
and
Ireland Ireland (, ; ; Ulster Scots dialect, Ulster-Scots: ) is an island in the North Atlantic Ocean, in Northwestern Europe. Geopolitically, the island is divided between the Republic of Ireland (officially Names of the Irish state, named Irelan ...
, very easily propagated by cuttings. It is a vigorous tree commonly reaching 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 An invasive species is an introduced species that harms its new environment. Invasive species adversely affect habitats and bioregions, causing ecological, environmental, and/or economic damage. The term can also be used for native spec ...
in various parts of the world, including: all states and territories in
Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
,
New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...
; the upper half of the
United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
;,
South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...
and
Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...
. In New Zealand it is listed on the
National Pest Plant Accord The National Pest Plant Accord (NPPA) is a New Zealand agreement that identifies pest plants that are prohibited from sale and commercial propagation and distribution. The Accord initially came into effect on 1 October 2001 between regional cou ...
, which means it cannot be sold or distributed. It can replace a
habitat In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ...
's native plant species diversity by forming monospecific stands. As only the male plant is present in New Zealand no fruit is formed unless hybridised. Species spread is facilitated by stem fragmentation which are carried via waterways and nearby adult individuals. Control and management for
habitat restoration Ecological restoration, or ecosystem restoration, is the process of assisting the recovery of an ecosystem that has been degraded, damaged, destroyed or transformed. It is distinct from conservation in that it attempts to retroactively repair ...
projects often uses
herbicide Herbicides (, ), also commonly known as weed killers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page f ...
s.


References


External links


USFS—United States Forest Service: ''Salix fragilis'' — "Weed of the Week"

Center for Invasive Species and Ecosystem Health—Invasive.org
— ''photos gallery''. * {{DEFAULTSORT:Salix fragilis fragilis Trees of Europe Flora of Western Asia Garden plants of Europe Flora of Ukraine Ornamental trees Plants described in 1753 Taxa named by Carl Linnaeus Plant nothospecies