Salix

White willow Salix alba, photographed by Willow.

Belongs within: Salicaceae.

Salix, the willows, is a genus of wind-pollinated trees and shrubs found mostly in arctic to temperate regions. Many species are grown as ornamentals and some have become widely invasive outside their native ranges. These include the weeping willow S. babylonica, a native of northeastern Asia of which selected varieties are grown for their pendulous habit.

The Duke of Bedford’s willow
Published 7 December 2022

Over the centuries, the activities of gardeners and horticulturalists have greatly expanded the scope of plant diversity. Walk through any significant collection of cultivated flora and you are likely to see multiple varieties that would have never existed without human intervention. These days, the naming of such cultigens is the purview of the International Code of Nomenclature for Cultivated Plants, a distinct system running parallel and supplementary to the botanical code for naturally occurring taxa. Under this code, cultivated varieties are granted non-Latinised names appended to their botanical parent, such as Rosa filipes ‘Kiftsgate’. In the earlier days of botanical nomenclature, however, there was no such clear separation. Many older horticultural varieties were bestowed with formal Latin names, one such being the Bedford willow Salix fragilis var. russelliana.

Salix fragilis var. russelliana, from Stephenson & Churchill (1837).

The Bedford willow was first described as a distinct species by James Smith in 1804 (Elwes & Henry 1913). There followed an extended history of debate as to the exact identity of Smith’s taxon, far too convoluted and tedious to be worth examining here*, but the name is now associated with a variant of the crack willow Salix fragilis. This species is distinguished by broadly lanceolate leaves, about four times as long as wide, with largely glabrous surfaces and coarsely serrated margins. The vernacular name of the ‘crack willow’ refers to the ease with which young branches break from the tree. The lost branches are then capable of taking root and growing into new trees. Crack willows are therefore abundant along riverbanks in much of Europe, including in Great Britain where they are introduced.

*Willow nomenclature in general has a long history of confusion. As quoted by Meikle (1992), the 19th Century willow expert William Borrer is supposed to have taken offence at a remark that “all sensible botanists eschewed Willows, while the crazy ones had each their own ideas about the species”.

The Bedford willow seems to have been first recorded in Leicestershire in the mid-1700s by Robert Bakewell (yes, that Robert Bakewell). It was then promoted as a commercial tree by Francis Russell, Duke of Bedford, hence the vernacular name (Meikle 1992). Willow species have separate male and female trees, and the Bedford willow is only known from female trees that are/were propagated vegetatively. The differences between the Bedford variety and the standard crack willow have not always been clear, and some accounts make them sound positively pornographic: that is, impossible to define but immediately recognisable. Individuals attributable to Salix fragilis var. russelliana usually grow taller than wild-type S. fragilis with a narrower crown. The twigs are supposedly less readily detached from their bases, and leaves tend to be shorter and more pubescent below, at least when young.

Johnson’s willow, an large individual tree in Lichfield, Staffordshire, that became known as a favourite of Samuel Johnson. Painted in about 1800 by an unknown artist, from the Samuel Johnson Birthplace Museum. Elwes & Henry (1913) identify this tree as a Bedford willow.

The exact origins of the Bedford willow are uncertain. Some have suggested hybrid origins between Salix fragilis and the closely related white willow S. alba, explaining the presence of pubescence in young leaves. However, as pointed out by Meikle (1992), the standard hybrid between the two species (known under the name S. × rubens) is clearly more intermediate in appearance between the two parents. Nevertheless, as the hybrid itself remains fertile, it would be possible for further introgression to occur. There is also some mystery about its history following discovery. Elwes & Henry (1913) considered the possibility that Smith’s original ‘S. russelliana’ was then lost to cultivation but Meikle (1992) would later describe S. fragilis var. russelliana as more abundant in Great Britain than wild-type S. fragilis. The most likely explanation for this discrepancy is simply the aforementioned confusion over the variety’s identity but there is another point worthy of consideration. Because the Bedford willow is known only from female trees, it has long been presumed to exist as a population of vegetative clones. However, a study of genetic variation in Belgian willows by De Cock et al. (2003) found too high a divergence between individuals of ‘S. fragilis var. russelliana’ for them to be clonal. Perhaps, they suggested, the ‘russeliana’ morphotype has appeared multiple times among crack willow populations. Perhaps not all such willows truly carry the Bedford heritage.

Systematics of Salix

Characters (from George W. Argus): Shrubs or trees, slightly heterophyllous, clonal or not, clones formed by root shoots, rhizomes, layering, or stem fragmentation; branching sympodial. Stems not spinose. Buds 1-scaled (rarely oily), margins connate into calyptra or distinct and overlapping adaxially, scale inner membranaceous layer usually not separating from outer layer, sometimes free and separating). Leaves deciduous or marcescent; stipules persistent, caducous, or absent (varying in presence and size on early and late leaves); petiole glandular-dotted or lobed distally; (blade often more than twice as long as wide, venation usually pinnate, margins entire, crenulate, crenate, serrate, serrulate, or spinulose-serrulate, teeth gland-tipped). Inflorescences axillary or subterminal, catkins, erect, spreading, or ± pendulous, sessile or terminating flowering branchlets, usually unbranched; floral bract apex entire, erose, bifid, or irregularly toothed; pistillate bract persistent or deciduous after flowering. Pedicels present or absent. Flowers: (sessile), perianth reduced to adaxial nectary (rarely also abaxial nectary, then distinct or connate into shallow cup); stamens 1, 2, or 3-10; filaments distinct or connate; ovary (stipitate or sessile), 2-carpellate; ovules (2-)4-24(-42) per ovary; styles usually connate, sometimes distinct distally; stigmas 2, entire or 2-lobed (less than 2 mm). Fruits capsular, (2-valved, obclavate to ovoid or ellipsoid). Seeds: aril present. x = 19.

<==Salix [incl. Chosenia]T00
    |--S. subg. SalixK07c
    |    |  i. s.: S. babylonica Linnaeus 1753K05 [incl. S. japonicaLO98]
    |    |--S. sect. SalixK07c
    |    |    |--S. alba Linnaeus 1753K07c
    |    |    |    |--S. a. var. albaV09
    |    |    |    `--S. a. var. vitellinaV09
    |    |    |--S. fragilis Linnaeus 1753K07c
    |    |    |    |--S. f. var. fragilisV09
    |    |    |    `--S. f. var. russellianaV09
    |    |    `--S. × rubens Schrank 1789K07c [S. fragilis × S. albaK07a]
    |    |         |--S. r. nothvar. rubensV09
    |    |         `--S. r. nothvar. basfordiana [S. alba var. vitellina × S. fragilis]V09
    |    |--S. (sect. Amygdalinae) triandra Linnaeus 1753K05
    |    `--S. (sect. Pentandrae) pentandra Linnaeus 1753K07c
    |--S. subg. ChametiaK07c
    |    |--S. (sect. Chamaetia) reticulata Linnaeus 1753K07c
    |    |    |--S. r. ssp. reticulataH93
    |    |    `--S. r. ssp. nivalisH93
    |    |--S. sect. GlaucaeK07c
    |    |    |--S. glauca Linnaeus 1753K07c
    |    |    `--S. glaucosericea Floderus 1943K07c
    |    |--S. (sect. Myrtilloides) myrtilloides Linnaeus 1753K06
    |    `--S. (sect. Retusae) retusa Linnaeus 1763K07c
    `--S. subg. VetrixK07c
         |  i. s.: S. helix [S. purpurea × S. viminalis]K07a
         |         S. × smithiana [S. cinerea × S. viminalis]V09
         |--S. sect. VetrixK07c
         |    |--S. appendiculata Villars 1789K07c
         |    |--S. atrocinerea Brotero 1804K05
         |    |--S. aurita Linnaeus 1753K07c
         |    |--S. caprea Linnaeus 1753K07c
         |    |--S. cinerea Linnaeus 1753K07c
         |    |    |--S. c. ssp. cinereaV09
         |    |    `--S. c. ssp. oleifoliaV09
         |    `--S. × reichardtii [S. caprea × S. cinerea]V09
         |--S. sect. ArbuscellaK07c
         |    |--S. foetida Schleich ex de Candolle 1805K05
         |    |--S. phylicifolia Linnaeus 1753K07c
         |    `--S. waldsteiniana Willdenow 1806K05
         |--S. sect. DaphnellaK07c
         |    |--S. acutifolia Willdenow 1806K07c
         |    `--S. daphnoides Villars 1789K07c
         |--S. (sect. Hastatae) hastata Linnaeus 1753K07c
         |--S. (sect. Helix) purpurea Linnaeus 1753K07c
         |--S. sect. NigricantesK07c
         |    |--S. mielichhoferi Sauter 1849K07c
         |    `--S. myrsinifolia Salisbury 1796K07c
         |--S. sect. VillosaeK07c
         |    |--S. helvetica Villars 1789K07c
         |    `--S. lapponum Linnaeus 1753K07c
         `--S. (sect. Vimen) viminalis Linnaeus 1753K07c
Salix incertae sedis:
  S. acuminata Miller 1768K07b
  S. amygdalinaA81
  S. amygdaloidesB75
  S. annularisC55b
  S. arctica Pallas 1788K07c [incl. S. anglorum var. antiplastaH93, S. anglorum var. petraeaH93]
  S. anticecrenata [incl. S. anticecrenata mstr. monadelpha]O88
  S. bebbianaH93
  S. bhutanensisO88
  S. boothii [incl. S. pseudocordata]H93
  S. brachycarpaH93
  S. breweriH93
  S. buergerianaLO98
  S. caesiaC55a
  S. calyculataO88
  S. capraeaRCT96
  S. carolinianaM83
  S. cascadensisH93
  S. daltonianaO88
  S. delnortensisH93
  S. discolorSF96
  S. drummondiana [incl. S. drummondiana var. subcoerulea]H93
  S. eastwoodiaeH93
  S. elaeagnosK06
  S. eriocephalaSF96
  S. eriostachyaO88
  S. exigua (see below for synonymy)H93
  S. geyeriana [incl. S. geyeriana var. argentea]H93
  S. gooddingii [incl. S. gooddingii var. variabilis]H93
  S. herbaceaCS77
  S. hookeriana [incl. S. piperi]H93
  S. humboldtianaF11
  S. hylematicaO88
  S. interiorB75
  S. jacquinianaC55a
  S. jepsonii [incl. S. sitchensis var. angustifolia, S. sitchensis var. ralphiana]H93
  S. kareliniiO88
  S. kirilowianaS00
  S. laevigata [incl. S. laevigata var. araquipa]H93
  S. lasiolepis (see below for synonymy)H93
  S. laurinaD37
  S. lemmoniiH93
  S. ligulifoliaH93
  S. lindleyanaO88
    |--S. l. var. lindleyanaO88
    `--S. l. var. microphyllaO88
  S. lucidaH93
    |--S. l. ssp. lucidaH93
    |--S. l. ssp. caudata [incl. S. caudata var. bryantiana]H93
    `--S. l. ssp. lasiandra [incl. S. lasiandra var. abramsii, S. lasiandra var. lancifolia]H93
  S. lutea [incl. S. lutea var. watsonii]H93
  S. melanopsis [incl. S. melanopsis var. watsonii]H93
  S. myrsinitesC55b
  S. myrtillaceaO88
  S. nigraBV06
  S. oreophilaO88
  S. oresteraH93
  S. ovatomicrophyllaO88
  S. pedicellataR-CT01
  S. planifolia [incl. S. phylicifolia var. monica]H93
  S. prolixa [incl. S. mackenzieana]H93
  S. psilostigmaO88
  S. pycnostachyaO88
  S. repens Linnaeus 1753K05
  S. rosmarinifoliaK06
  S. sclerophyllaO88
  S. scouleriana [incl. S. scouleriana var. coetanea]H93
  S. sericeaSF96
  S. sericocarpaO88
  S. serpyllumO88
  S. sessilifolia [incl. S. parksiana]H93
  S. sikkimensisO88
  S. silesiaca Willdenow 1806K05
  S. sitchensis [incl. S. coulteri]H93
  S. sphenophylla Skvortsov 1966K07c
  S. subfragilis [incl. S. nipponica]LO98
  S. tetraphyllaP03
  S. tetraspermaM72
  S. varians Goeppert 1855HL08
  S. wallichianaSS72

Salix exigua [incl. S. hindsiana, S. hindsiana var. leucodendroides, S. hindsiana var. parishiana, S. exigua var. stenophylla]H93

Salix lasiolepis [incl. S. lasiolepis var. bigelovii, S. lasiolepis var. bracelinae, S. lutea var. nivaria, S. lasiolepis var. sandbergii, S. tracyi]H93

*Type species of generic name indicated

References

[A81] Adler, H. 1881. Les Cynipides. 1re partie. Introduction. La génération alternante chez les cynipides, traduit et annoté par J. Lichtenstein, suivi de la classification des cynipides d’après le Dr G. Mayr. C. Coulet: Montpellier.

[B75] Bowles, J. B. 1975. Distribution and biogeography of mammals of Iowa. Special Publications, The Museum, Texas Tech University 9: 1–184.

[BV06] Brack, V., Jr & R. K. La Val. 2006. Diet of the gray myotis (Myotis grisescens): variability and consistency, opportunism, and selectivity. Journal of Mammalogy 87 (1): 7–18.

[C55a] Candolle, A. de. 1855a. Géographie Botanique Raisonée: Ou exposition des faits principaux et des lois concernant la distribution géographique des plantes de l’époque actuelle vol. 1. Librairie de Victor Masson: Paris.

[C55b] Candolle, A. de. 1855b. Géographie Botanique Raisonée: Ou exposition des faits principaux et des lois concernant la distribution géographique des plantes de l’époque actuelle vol. 2. Librairie de Victor Masson: Paris.

[CS77] Cramp, S., & K. E. L. Simmons (eds) 1977. Handbook of the Birds of Europe, the Middle East and North Africa: The Birds of the Western Palaearctic vol. 1. Ostrich to Ducks. Oxford University Press: Oxford.

De Cock, K., B. Lybeer, K. Vander Mijnsbrugge, A. Zwaenepoel, P. Van Peteghem, P. Quataert, P. Breyne, P. Goetghebeur & J. Van Slycken. 2003. Diversity of the willow complex Salix albaS. × rubensS. fragilis. Silvae Geneticae 52 (3–4): 148–153.

[D37] Dobzhansky, T. 1937. Genetics and the Origin of Species. Columbia University Press: New York.

Elwes, H. J., & A. Henry. 1913. The Trees of Great Britain and Ireland vol. 7. Privately printed: Edinburgh.

[F11] Fraga, R. M. 2011. Family Icteridae (New World blackbirds). In: Hoyo, J. del, A. Elliott & D. A. Christie (eds) Handbook of the Birds of the World vol. 16. Tanagers to New World Blackbirds pp. 684–807. Lynx Edicions: Barcelona.

[HL08] Henniger, M., & R. Leder. 2008. Eozäne Makroflora der Querfurter Mulde. Mauritiana 20 (2): 229–251.

[H93] Hickman, J. C. (ed.) 1993. The Jepson Manual: Higher Plants of California. University of California Press: Berkeley (California).

[K05] Kopelke, J.-P. 2005. The species of the Pontania proxima group in Europe (Hymenoptera, Tenthredinidae, Nematinae). Senckenbergiana Biologica 85 (1): 85–95.

[K06] Kopelke, J.-P. 2006. Description of the female of Euura myrtilloides Kopelke 1996, with a key to the European species of the atra-group (Hymenoptera, Tenthredinidae, Nematinae). Senckenbergiana Biologica 86 (1): 75–84.

[K07a] Kopelke, J.-P. 2007a. The European species of the genus Phyllocolpa, part I: the leucosticta-group (Insecta, Hymenoptera, Tenthredinidae, Nematinae). Senckenbergiana Biologica 87 (1): 75–109.

[K07b] Kopelke, J.-P. 2007b. The European species of the genus Phyllocolpa, part II: the leucaspis-group (Insecta, Hymenoptera, Tenthredinidae, Nematinae). Senckenbergiana Biologica 87 (2): 149–161.

[K07c] Kopelke, J.-P. 2007c. The European species of the genus Phyllocolpa, part III: the species-groups of crassispina, scotaspis, and piliserra (Insecta, Hymenoptera, Tenthredinidae, Nematinae). Senckenbergiana Biologica 87 (2): 163–183.

[LO98] Lack, H. W., & H. Ohba. 1998. Die Xylothek des Chikusai Kato. Willdenowia 28: 263–276.

Meikle, R. D. 1992. British willows; some hybrids and some problems. Proceedings of the Royal Society of Edinburgh. Section B. Biological Sciences 98: 13–20.

[M72] Mitra, S. N. 1972. Observations on the vegetation of the Upper Damodar catchment area. Journal of the Bombay Natural History Society 69 (1): 17–25.

[M83] Myers, R. L. 1983. Site susceptibility to invasion by the exotic tree Melaleuca quinquenervia in southern Florida. Journal of Applied Ecology 20: 645–658.

[O88] Ohba, H. 1988. The alpine flora of the Nepal Himalayas: an introductory note. In: Ohba, H., & S. B. Malla (eds) The Himalayan Plants vol. 1. The University Museum, University of Tokyo, Bulletin 31: 19–46.

[RCT96] Ragusa Di Chiara, S., & H. Tsolakis. 1996. A. survey of phytoseiid mites (Phytoseiidae) associated with various plants in Sicily (Italy). In: Mitchell, R., D. J. Horn, G. R. Needham & W. C. Welbourn (eds) Acarology IX vol. 1. Proceedings pp. 253–256. Ohio Biological Survey: Columbus (Ohio).

[R-CT01] Ragusa-di Chiara, S., & H. Tsolakis. 2001. Phytoseiid faunas of natural and agricultural ecosystems in Sicily. In: Halliday, R. B., D. E. Walter, H. C. Proctor, R. A. Norton & M. J. Colloff (eds) Acarology: Proceedings of the 10th International Congress pp. 522–529. CSIRO Publishing: Melbourne.

[S00] Siddiqi, M. R. 2000. Tylenchida: Parasites of plants and insects 2nd ed. CABI Publishing: Wallingford (UK).

[SS72] Singh, V., & H. Singh. 1972. A contribution to the flora of Gangolihat block in Pithoragarh District. Journal of the Bombay Natural History Society 69 (2): 352–368.

[SF96] Smith, D. R., & R. S. Fritz. 1996. Review of the eastern United States species of the leaf-folding sawflies of the genus Phyllocolpa Benson (Hymenoptera: Tenthredinidae). Proceedings of the Entomological Society of Washington 98 (4): 695–707.

[T00] Thorne, R. F. 2000. The classification and geography of the flowering plants: dicotyledons of the class Angiospermae (subclasses Magnoliidae, Ranunculidae, Caryophyllidae, Dilleniidae, Rosidae, Asteridae, and Lamiidae). The Botanical Review 66: 441–647.

[V09] Verdcourt, B. (ed.) 2009. Additions to the wild fauna and flora of the Royal Botanic Gardens, Kew. XXVI. Miscellaneous records. Kew Bulletin 64 (1): 183–194.

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