WILLOW TREE (עֲרָבָה, H6857, sometimes called Salix Tree; צַפְצָפָה, H7628, waterwillow or osier).
The willow tree, or trees, are mentioned six times in Scripture—five times as ’ereb and once as ṩapṩāpâ in Ezekiel 17:5. The other references are Leviticus 23:40; Job 40:22; Psalm 137:2; Isaiah 15:7 and 44:4. Perhaps the most famous of the texts comes from Psalm 137 because of the folk song which made it famous, viz. “I’ll hang my harp on the weeping willow tree.”
The “green withs” with which Samson was bound (Judg 16:7) prob. came from willows, while the reference in Amos 6:14 to “river of the wilderness” (KJV) may well have been “willow river” or, as Moffatt trs. it, “torrent of willows.”
Did the harps of Psalm 137 hang on the willow known as Salix babylonica? Hence “by the waters of Babylon there I’ve sat down and wept” (Ps 137:1)—the seeming connection with the species and weeping. The writer has failed to prove that babylonica was ever found in Pal.—whereas botanists know over twenty other kinds of willows growing in that country.
A choice must be made between the following Salixes—Salix alba, Salix acmophylla, Salix fragilis and Salix safsaf, all of which grow well in Pal. esp. alongside the streams. The most probable species is Salix safsaf, because it resembles the Heb. word ṩapṩāpâ.
Moffatt prefers the poplar when tr. “ereb” in Psalm 137:2. This is the Populus euphratica.
International Standard Bible Encyclopedia (1915)
Comparison with the Arabic cafcaf, "the willow," makes it very probable that thc translation of Eze 17:5 is correct.