Boyd’s Bible Dictionary:

(field speaker). A narcotic plant, resembling rhubarb, bearing a yellow, aromatic fruit (Gen. 30:14-16; Song of Sol. 7:13).

Concise Bible Dictionary:

Some strong-smelling plant found in the fields of Palestine. Many opinions have been expressed as to what herb is referred to. It is possibly the Mandragora officinarum, called the “love apple,” a relative to the “apple of Sodom.” The Atropa mandragora is another species (Gen. 30:14-16; Song of Sol. 7:13).