Salix L.
Genus of about 400 species distributed mainly across the Northern Hemisphere. Delineation of the species has posed many problems since they hybridise easily, with many intermediate specimens between two species and other introgressed specimens (assimilated to a species, but with some characters from another). In North Africa there are 8 species occurring in the Mediterranean area and permanent wetlands of northern Sahara: 3 are widely distributed (S. atrocinerea, S. pedicellata and S. purpurea). S. alba and S. fragilis are 2 closely related species with an unknown distribution and have often been confused. A further 2 species have a much localised distribution across northern rivers (S. triandra and S. eleagnos). Finally, S. mucronata is widespread across western Asia and tropical Africa, penetrating the North African Mediterranean through Egypt, reaching towards the W to NE Libya.
The willows have a porous and white, not very resistant wood, and are not very palatable to livestock. However, they have an exceptional forestry value in areas where floods cause serious recurrent damage. They take root easily and can be used extensively in the reforestation of riverbanks to curb the erosion of their margins and reduce the strength and speed of the water. Some species require dry to humid bioclimate (S. alba, S. triandra, S. eleagnos and S. atrocinerea). But others, like S. purpurea or more specifically S. pedicellata, are well adapted to drier terrains where water may be lacking from the riverbeds for several months to a year.
Díaz González, T.E. & Llamas, F. 1987 Aportaciones al conocimiento del género Salix L. (Salicaceae) en la provincia de León (NO España). Acta Botánica Malacitana, 12: 111-150.
Immelman, K.L. 1987. Synopsis of the genus Salix (Salicaceae) in southern Africa. Bothalia 17.2: 171-177.
Mateos, M.A. & Valdés, B. 2009. Catálogo de la flora vascular del Rif occidental calizo (N de Marruecos). I. Selaginellaceae-Rosaceae. Lagascalia, 29: 105-257.
General identification key using leaf characters
1 Leave sand buds mostly opposite Salix purpurea
1 Leaves alternate 2
2 Adult leaves glabrescent on the upper side and appressed-sericeous (silky) on the underside, large trees when mature Salix alba
2 Adult leaves without appressed-sericeous hairs, although they may have other trichomes, Shrubs or trees 3
3 Adult leaves glabrous 4
3 Adult leaves pubescent or tomentose 7
4 Trees, leaves with glands ± branched at the junction of the leaf blade with the petiole Salix fragilis
4 Trees or shrubs, leaves with glands at the junction of the leaf blade with the petioleor if there are any, small and simple 5
5 Stipules very small and ephemeral, so it can be easily confused with species without stipules Salix mucronata
5 Stipules large and permanent, ± cordiform 6
6 Adult branches reddish. Buds glabrous. Leaves with serrated glandulous margin Salix triandra
6 Adult branches greyish. Buds pubescent. Leaves with eglandular margin, entire to serrulate Salix pedicellata
7 Leaves obovate-oblong or lanceolate, ± elliptical, adult leaves glabrous or glabrescent and lustrous on the upper side, margin entire or not with no clear teeth and some reddish-ferruginous hairs on the upper side or on the underside Salix atrocinerea
7 Adult leaves linear or linear-lanceolate, 10-15 times longer than wide, white-tomentose underside Salix eleagnos
Identification key for male plants
1 Flowers with (5)7-9(10) stamens Salix mucronata
1 Flowers with 2-3 stamens 2
2 Flowers with 3 stamens Salix triandra
2 Flowers with 2 stamens 3
3 Staminal filaments partly or completely fused 4
3 Staminal filaments free 5
4 Staminal filaments completely fused up to the anthers; aments usually opposite or subopposite Salix purpurea
4 Staminal filaments fused only in the lower half; aments alternate Salix eleagnos
5 Floral bracts uniformly coloured 6
5 Floral bracts bicoloured, darker at the apex 7
6 Aments lax; leaves sericeous, without glands or with glands ± or not branched at all, at the junction between the leaf blade and the petiole Salix alba
6 Aments dense; leaves glabrous, with ± branched glands at the junction between the leaf blade and the petiole Salix fragilis
7 Staminal filaments glabrous or subglabrous on the lower third Salix pedicellata
7 Staminal filaments hairy on the lower third, leaves with some ferruginous hairs Salix atrocinerea
Identification key for female plants
1 Female flowers with 2 nectaries 2
1 Female flowers with 1 nectary 3
2 Branches ± pendulous, leaves with no branched glands at the junction between the leaf blade and the petiole Salix mucronata
2 Branches ascending, leaves with branched glands at the junction between the leaf blade and the petiole Salix fragilis
3 Ovary and capsule completely or partially tomentose or pubescent 4
3 Ovary and capsule hairless 5
4 Ovary and capsule sessile or subsessile (peduncle shorter than the nectary) Salix purpurea
4 Ovary and capsule pedunculate (peduncle longer than the nectary) Salix atrocinerea
5 Aments precocious (that develop before the leaves) Salix pedicellata
5 Aments coeval to the leaves, subcoeval or late 6
6 Ovary with a peduncle longer than the nectary Salix triandra
6 Ovary sessile or with the peduncle shorter that nectary 7
7 Caducous bracts; trees Salix alba
7 Persistent bracts; shrubs Salix eleagnos
Updated by: F. Alcaraz & J. Charco.