There are several problems in determining with accuracy the plants called willows in the Bible. For example, the willows referred to in Psalm 137, the "willows of Babylon," are not true willows but rather a kind of poplar. There are several species of willow in the Middle east, two of the more common are Salix acmophylla and S. alba. The Bible does not indicate which species are meant. Willows are common along watercourses and form dense thickets along the banks of the Jordan, especially in its upper reaches. Willows are mentioned in only four places: Leviticus 23:40, Job 40:22, Isaiah 15:7 and Isaiah 44:4.
The willow is a much branched shrub with narrow, pointed leaves that are lighter on the bottom surface. Each shrub is unisexual and the flowers are minute and borne in the spring. The seeds are equipped with hairs that enable them to float through the air and ensure their dispersal. For centuries the bark of the willow has been used as a medicine and it is from the willow bark that aspirin was first extracted.
In Scripture, the willow is always associated with a brook or river, that is, with a perpetual source of nourishment and supply. This application is evident from Isaiah 44:4, "And they shall spring up among the grass, as willows by the watercourses." This is a different allusion than that in Psalm 1:3 and Jeremiah 17:8 where the emphasis is on being planted and on yielding fruit. In the case of the willow, the emphasis is on the vigor of the growth and the intimate association with the watercourse.
The wood of willow is soft and not very durable. One of the traditional uses of willow wood in Syria is for forms for darning clothing. Willow wood is cut into egg-shaped structures that will fit into a sock.