Shrub, prostrate and up to 20 cm in Svalbard (up to 3 m or more in northernmost Norway). Extensively branched above ground and probably also below ground, forming a small, clonal stand in Helvetiadalen, one of its two known localities in Svalbard today (see Distribution). Main branches terete, up to 10 mm thick, dark grey, glabrous or nearly so, dull. Younger branches 2–4 mm thick, brownish red. Last year's twigs densely hairy with up to 1 mm long, patent or spreading, yellowish white hairs; older twigs more sparsely pubescent. Buds dimorphic (of two kinds). Vegetative buds (growing into leafy shoots) small, 3–5 × 1.5–2.5 mm, oblong, obtuse, brownish red, glabrous or sparsely pubescent. Generative buds (growing into spikes) much larger and broader, 6–9 × 6–9 mm, nearly globular. Flowering mainly before the leaves appear.

The Svalbard plants do not fully develop their leaves, and they flower only intermittently. Description of leaf, inflorescence, flower and fruit therefore based partly on plants (rooting twigs) from Svalbard taken into cultivation in Tromsø, partly on plants from northernmost Russia (Novaya Zemlya).

Leaves alternate. Entire leaf sparsely or densely pubescent with long soft hairs but usually not so densely that it covers the surface (and the colour of stipules and blades). Petiole much shorter than blade, when well developed with two large acute stipules with margin entire or with sparse sessile yellow glands. Blade oblong or broadly oblong with base truncate or cuneate, margin entire or with very few sessile yellow glands, apex usually acute, upper surface green with slightly impressed main veins, lower surface paler green with raised main veins, with a sparse or moderately dense pubescence of long lanate white hairs.

The inflorescences of Salix are more or less dense, pedunculate, many-flowered spikes. The plants are unisexual. The flowers are without any perianth but supported by bracts. The male flower consists of 2 stamens (in all arctic species, 1–5 or rarely more in some southern species) and a scale-like gland between the stamens and the spike mid axis. The female flower consists of a sessile or short-stalked, fused gynoecium of 2 carpels, with a style and a stigma with 2–4 branches, and a gland similar to that of the male flower. The fruit is a one-roomed capsule with numerous seeds with long hairs facilitating dispersal.

Only male plants known from the Helvetiadalen site in Svalbard today. The plants from the second site, in Longyearbyen, have not been investigated. Spikes dense, many-flowered, terminal or lateral on shoots, appearing well before the leaves, on short peduncles with reduced (scaly) leaves. Bracts oblong or ovate, obtuse, dark brown or blackish, with 3–6 mm long yellow hairs on both surfaces and in the margin, making the spikes very conspicuous (and beautiful) before and during flowering. Male spikes up to 5(8) × 1.5(2) cm. Anthers yellow. Female spikes may be very large, to 10 × 2 cm. Gynoecium glabrous, yellowish green or reddish; styles yellowish, long, apically cleft into 2–4 long stigmatic branches.

Fruit not observed in Svalbard. The fruit is a yellowish to reddish capsule, ca. 5–6 x 2 mm, with numerous seeds with long hairs facilitating dispersal.

Sexual reproduction by seeds, but not in Svalbard. An obligate outcrosser due to being dioecious (separate male and female plants). Pollination probably both by wind and insects (mainly the last). However, only male shrubs have been observed yet in Svalbard, flowering intermittently.

The seeds have long hairs and are dispersed by wind.

As this is the only (potentially) shrubby species of Salix in Svalbard, there is no possibility of confusion (today, but see Comments for the previous confusions concerning this plant in Svalbard). It differs from the other species of Salix in the islands in thick, densely hairy twigs, leaves with long, soft hairs, and yellow spikes appearing before the leaves. As for other shrubs and dwarf shrubs, Salix is the only genus where the buds are covered by a single bud scale (easily observed with a lens).

The Helvetiadalen site is on the brink of a brook terrace with meadow character, eroded from the brook. The Longyearbyen site has not been investigated yet.

Thermophilous. Salix lanata has been known from three localities in Svalbard, all on Spitsbergen in the middle arctic tundra zone and the weakly continental section. One shrub close to the air strip in Ny-Ålesund at Kongsfjorden (Oscar II Land) was grazed to death by reindeer introduced by the Norwegian Polar Institute in 1990/1991. The few twigs collected before its extinction document that it belong to S. lanata. A very few plants, probably clonal, were discovered in 1963 in Helvetiadalen, a tributary valley to Adventdalen (Nordenskiöld Land). This stand is still extant, but the plants have only been observed with flower (spike) buds once (1964). Twigs were taken into culture in Tromsø in 2002 and flowered, confirming the identity as S. lanata (by G. Argus, A.K. Skvortsov, and R. Elven, pers. comm.). In 2017 the species was discovered within Longyearbyen (road 224.5) by P. Lutnæs, confirmed as this species by P.B. Eidesen, but plants from this locality have not yet been studied further.

The 'population' in Adventdalen consists of four male plants or mini-clones within an area of 10 × 30 m, in a seepage on a terrace brink faced by erosion. The plant is acutely endangered and will disappear within short time.

Salix lanata is otherwise a N European and W Siberian species, replaced eastwards in Russia and also in W North America by the related S. richardsonii Hook., in E North America by the related S. calcicola Fernald & Wiegand. The presence of this species in Svalbard is rather surprising, see Comments.

This single shrubby Salix known from the Svalbard islands has been a matter of discussion since its discovery. Because it never has been found flowering there, and as the species of Salix are notoriously difficult to identify, it has gone through four taxonomic revisions. As first, it was assigned to S. glauca L., then to S. callicarpaea Trautv. (now considered a western arctic race of S. glauca, namely ssp. callicarpaea (Trautv.) Böcher), then for more than a decade to S. arctica Pall. (by Elven in Lid & Lid 1994; Elven & Elvebakk 1996; Pálsson 2000 in Flora Nordica). Its true identity as S. lanata was not confirmed before the twigs transplanted to Tromsø grew larger, flowered and showed the decisive features (yellow hairs on bracts, stipules, venation and pubescence of leaves).

Salix lanata has only been known from three localities in Spitsbergen, 120 km apart, in one of these sites with a single plant (now dead but documented in the herbaria before its demise), in a second site with a few barely surviving shrubs, and in a third site with an unknown number of shoots. Plants from both sites seem to belong to S. lanata, suggesting that this species may have had a larger range in Svalbard previously (see below). All 'populations' were already evolutionary and reproductively dead when discovered: at Ny-Ålesund a single individual (of a dioecious species), in Helvetiadalen a clone of male plants, and in Longyearbyen probably one isolated shrub.

The find of just S. lanata in Svalbard is unexpected as this is not by far the most hardy of shrubby Salix in the Arctic. It reaches north to the middle arctic tundra in Russia. Salix reptans Rupr., a Russian relative of S. glauca L., is much more hardy, reaching the border between the northern arctic tundra and the polar desert zones and is common both on Novaya Zemlya and the European mainland nearly west to the Norwegian border in the Murman area. Another and much more hardy arctic shrub is S. arctica Pall., perhaps the most widespread of all arctic Salix and reaching the northern arctic tundra in both N Greenland and Novaya Zemlya (and perhaps on the Murman coast), and in addition replacing S. glauca in Iceland and having reached Jan Mayen at least twice. See Elven et al. (2011; distribution table).

For the morphological variation and infraspecific taxonomy of S. lanata, see Elven & Karlsson (2000) and Elven et al. (2013). Two entities are recognized as S. lanata s. str. (ssp./var. lanata) and ssp. glandulifera (Flod.) Hiitonen (S. glandulifera Flod.; S. lanata var. glandulosa Wahlenb.). The available Svalbard material of S. lanata is very restricted but we provisionally assign it to var. lanata.

Elven, R. & Elvebakk, A. 1996. Part 1. Vascular plants. – In: Elvebakk, A. & Prestrud, P. (eds.), A catalogue of Svalbard plants, fungi, algae, and cyanobacteria. – Norsk Polarinstitutts Skrifter 198: 9–55.

Elven, R., Fremstad, E. & Pedersen, O. (eds.) 2013. Distribution maps of Norwegian vascular plants. IV The eastern and northeastern elements. – Akademika Publishing, Trondheim.

Elven, R. & Karlsson, T. 2000. Salix L. – In: Jonsell, B. (ed.), Flora Nordica 1 Lycopodiaceae – Polygonaceae: 117–188.

Elven, R., Murray, D.F., Razzhivin, V. & Yurtsev, B.A. (eds.) 2011. Annotated Checklist of the Panarctic Flora (PAF) Vascular plants. http://panarcticflora.org/

Engelskjøn, T., Alsos, I.G. & Lund, L. 2003. Twenty of the most thermophilous vascular plant species in Svalbard and their conservation status. – Polar Research 22: 317–339.

Lid, J. & Lid, D.T. 1994. Norsk Flora. Ed. 6 by R. Elven. – Det Norske Samlaget, Oslo.

Pálsson, J. 2000. Salix arctica Pall. – In: Jonsell, B. (ed.), Flora Nordica 1 Lycopodiaceae – Polygonaceae: 141–142.