Tristram thinks that by the "willow by the water-courses," the Nerium oleander, the rose-bay oleander, is meant. He says, "It fringes the Upper Jordan, dipping its wavy crown of red into the spray in the rapids under Hermon, and is nutured by the oozy marshes in the Lower Jordan nearly as far as to Jericho...On the Arnon, on the Jabbok, and the Yarmuk it forms a continuous fringe. In many of the streams of Moab it forms a complete screen, which the sun's rays can never penetrate to evaporate the precious moisture. The wild boar lies safely ensconced under its impervious cover."
M.G. Easton M.A., D.D., Illustrated Bible Dictionary, Third Edition,
published by Thomas Nelson, 1897. Public Domain, copy freely.
[S] indicates this entry was also found in Smith's Bible Dictionary
Bibliography InformationEaston, Matthew George. "Entry for Willows". "Easton's Bible Dictionary".