• River willows (Salix fluviatilis, aka Salicaceae):

Fast-growing pioneer trees and shrubs, dioecious, often reproducing clonally. The vast majority of species in the family are willow shrubs (Salix spp.), which commonly hybridize and make identification and enumeration of species numbers difficult. Temperate and boreal, with a few tropical representatives. Absent from Malesia, Australia, Oceania.  (source: http://www.treeguide.com/family.asp?FamilyID=244&Region=NorthAmerican )

• River willows in South Africa:
  

The River willow (Umngcunube in Xhosa) is found along river banks throughout South Africa, most particularly in the southern Free State, the western Cape (except west coast) and southern Namibia. It is a majestic tree, growing to about 15m in height. The characteristic willow foliage is summer growing, (the tree is deciduous) and augmented with small yellowish flowers between August and October. These are replaced with capsule shaped fruits which later split to release tufted woolly seeds. River willows are readily propagated, taking easily from truncheons and cuttings. Medicinal uses of this tree include treatment of rheumatism and fever. The tree contains salicyn (salicylic acid is a primary ingredient of Aspirin), which gives it anti-inflammatory properties. Although similar in appearance, the River willow is not to be confused with the Weeping willow (Salix babylonica) which is exotic but has become naturalised due to widespread planting. (source: http://www.dispatch.co.za/2000/08/26/features/GARDEN.HTM )