Boyd’s Bible Dictionary:
(soft). Jews’-mallows of the East, used for pot-herbs (Job 30:4).
Concise Bible Dictionary:
Some common herb which the poor would eat to satisfy their hunger (Job 30:4). The RV has “salt-wort.” Several have judged the herb to be the Atriplex halimus which has a sour taste, but not sufficiently so to prevent its being eaten.
Atriplex Halimus