Nomenclature
Scientific Name:
Salix viminalis L., Sp. Pl. 1021 (1753)
Synonymy:
Lectotype (chosen by Larssen, Nordic J. Bot. 15: 343, 1995): "Salix 27 viminalis, revoluta" (written on sheet), LINN 1158.82, image seen.
Vernacular Name(s):
basket willow; hemp willow; osier; silky osier
 Description

Multi-stemmed shrub. Branchlet wood without ridges or with sparse, short ridges 2–6 mm long. Current year's branchlets densely tomentose, the hairs not persistent, yellow to orange-yellow (UCL87–71). Flower buds 5.0 mm long, 1.8 mm wide, 1.3 mm deep, narrowly ovoid, 2-keeled, pubescent. Leaf buds hairy, densely short-silky. Leaves alternate, not falcate. Stipule 0.5–9 mm long, 0.7–3.0 mm wide, very narrowly ovate to linear, deciduous. Petiole 2.5–7 mm long, densely tomentose, groove present or absent, glands absent, base not expanded, pale yellow to yellow-green. Emerging leaves green, with moderately densely short-silky hairs. Proximal leaves entire. Leaf lamina 70–175 mm long, 5–20 mm wide, length to width ratio 6–15:1, very narrowly ovate to very narrowly elliptical; base rounded; apex very narrowly acute; leaf galls absent; margins crenate, slightly undulating, finely revolute to plane; upper lamina surface slightly bullate due to impressed veins, slightly to medium glossy, moderately densely tomentose or glabrous except for tomentum on the midvein, stomata absent; lower lamina surface midvein and usually side-veins raised, not glaucous to distinctly glaucous, densely short- to long-silky hairy. Catkin opening precocious to coetaneous with leaves, catkin flowers opening sequentially from base. Flowering branch 17–25 mm long, with 2 subtending leaves. Male catkin 23–24 mm long, 13 mm diameter; catkin rachis not visible between flowers. Female catkin 13–40 mm long, 6–11 mm diameter; catkin rachis not visible between flowers. Flower bract 2.0–2.7 mm long, 0.5–0.7 mm wide, black at the apex, otherwise green, flat; apex acute, densely long-silky hairy on both surfaces and margins. Male nectaries 1 or 2, inner nectary 0.6–0.7 mm long, 0.20–0.23 mm wide, green. Stamens 2, filaments free, glabrous; anthers 0.8–1.3 mm long, yellow, sometimes red-tinted. Female nectary 1, 0.6 mm long, 0.3 mm wide, yellow; ovary 2.2–2.6 mm long, densely short-silky hairy, equal to bract in length but style extending beyond the bract; stipe 0.8 mm long, style base 0.6 mm, style arms 0.9–1.4 mm long, sometimes unequal in length, unlobed to lobed to the style arm base, pale yellow-green.

 Recognition

Leaves are very narrowly elliptical or very narrowly ovate, 70–175 mm long, 5–20 mm wide, with margins crenate. The petiole is short (2–7 mm long). Leaves are persistently silky-hairy below. Female flowers have the ovary densely short-silky hairy, the style arms exceptionally long (0.9–1.4 mm) and unlobed to completely bilobed (all variation between these extremes occurs). The flower bract is ovate, black in the upper half, densely long-silky hairy, and equal in length to the ovary. Male flowers have two stamens and anthers are slightly red-tinted before opening. Skvortsov (1999) stated that the wood lacks ridges, but New Zealand specimens have very sparse, short ridges.

Salix viminalis is most similar to hybrids where S. viminalis is one of the parents, particularly hybrids with the presumed parentage S. caprea × S. cinerea × S. viminalis, formerly known as S. ×dasyclados. Skvortsov (1999, pp. 59–60) found that S. viminalis and S. ×dasyclados overlapped in features so much it was not possible to provide a key.

Another such hybrid present in New Zealand is Salix ×smithiana (S. caprea × S. viminalis), which has a wider leaf lamina (21–23 mm wide, rather than 6–20 mm wide in S. viminalis), branches that are somewhat brittle at their base, and petioles that are flat to convex adaxially.

Salix eleagnos is similar but leaves are smaller (2.6–4.5 mm wide versus 6–12 mm wide in S. viminalis), and the hairs on the underside of the leaves form a fuzzy tomentum (i.e. they are not appressed) while in S. viminalis they are appressed long-silky hairs.

Salix udensis and S. schwerinii are also similar to S. viminalis in leaf size and shape. Salix udensis has wider leaves than S. viminalis (26–30 mm wide in S. udensis versus 6–20 mm wide in S. viminalis) and has sparser short-silky hairs so that the lower leaf surface is visible between the hairs. Salix schwerinii has persistent stipules, while in S. viminalis they are deciduous.

 Distribution

Southern North Island (Manawatū River 1993; Oroua River 2003, Hutt River 1949), Sounds-Nelson (Motueka 1971), Westland (Hokitika River 1961, Okuru River 1983), Canterbury (Kaikōura 1971, Waitohi River 1963, Lowburn 1978, south bank of the Waimakariri River near S.H.1 1932, 1980, 1991; Christchurch City 1971–1995, Lake Roundabout 1979, Lake Pukaki 1970), Otago (Alexandra–Roxburgh 1982, Ōpihi–Omakau 1958, Kyeburn 1966, Middlemarch 1968, Capburn 1968, Manuherikia River 1968, 1986, Poolburn Creek 1966, Ida Burn 1966, Lowburn 1978, Cardrona Valley 1986, Ranfurly 1986, Naseby 1965, Oamaru 1966, Dunedin 1954, Burnside 1966).

 Biostatus
Exotic
 First Record

First collection: CHR 115427, C.E. Foweraker, 28 March 1932, "Waimak Road, Christchurch."

First publication: Mistral (2015) noted that S. viminalis was being sold in Christchurch in 1870. This willow, along with Salix purpurea and S. triandra, was grown commercially in New Zealand for basket-making. Allan (1940)​​​​​​​said, "Occasionally escapes from cultivation".

 Phenology

Flowering: Mid-August–early October.

 Cytology

Diploid, 2n = 38 (Argus 2010, CCDB based on 20 counts), provisionally confirmed by flow cytometry using PN312 and PN220 (labelled 'Gigantea'). However, two other clones, PN669 (Salix 'Aquatica Gigantea Korso') and PN245, are tetraploid and may be hybrids.

 Bibliography
Allan, H.H. 1940: A handbook of the naturalized flora of New Zealand. DSIR Bulletin. 83: 1–344. Government Printer, Wellington.
Argus, G.W. 2010: Salix. In: Flora of North America Editorial Committee (ed.) Flora of North America: Magnoliophyta: Salicaceae to Brassicaceae. Vol. 7. Oxford University Press, New York. 4–157.
Larsson, G. 1995: Nomenclatural remarks on the Salix viminalis group in Norden. Nordic Journal of Botany 15: 343–345.
Linnaeus, C. 1753: Species Plantarum. Impensis Laurentii Salvii, Stockholm.
Meikle, R.D. 1984: Willows and poplars of Great Britain and Ireland. BSBI Handbooks No 4. Botanical Society of the British Isles.
Mistral, M. 2015: To bend the willow: the basket willows (Salix spp.) in New Zealand. PhD thesis, University of Otago, Dunedin, PhD.
Skvortsov, A.K. 1999: Willows of Russia and adjacent countries. Taxonomical and geographical revision. Univ. Joensuu Fac. Math. Nat. Sci. Rep. Ser. 39: 1–307.