Or not. Please let me know if he's written about this already. (Update: R. Slifkin discusses the Adnei ha-sadeh is chapter 14 - "Vegetable Men and Tree Geese" - in his Sacred Monsters book. I thanks Frumheretic for bringing this to my attention.)
משנה כלאיים- פרק ח.ד ואדני השדה, חיה; רבי יוסי אומר, מטמאות באוהל כאדם
ירושלמי (כלאיים ח,ה): 'אבני(צ"ל אדני) השדה חיה' - ייסי ערקי (יש מפרשים: שם חכם; אבל יסטרוב מתקן:ר' יוסי אומר): בר נש דטור הוא. והוא חיי מן טיבורייה, איפסק טיבורייה לא חיי. רבי חמא בר עוקבא בשם רבי יוסי בן חנינה: טעמא דרבי יוסי 'וכל אשר יגע על פני השדה' (במדבר יט,טז) - בגדל על פני השדה
Basically (see Ra'av to that Mishna) this refers to a man who hs connected by an umbilical cord to the ground and if this cord is severed he dies. According to the Gra- the איש שדה
mentioned in Toledot 25:27 - ויהי עשו איש ידע ציד איש שדה; is this same Adnei Ha-Sadeh (The Ra'av identifies it with אוב)
Given that Josephus originates from the same background as the Amoraim of the Yerushalmi, I have no doubt that the following passage paralells that of the Yerushalmi.
In reference to the Mandrake root he writes (courtesy of Wikipedia - also see the next passage quoted and you will understand the identification with אוב):
According to the legend, when the root is dug up it screams and kills all who hear it. Literature includes complex directions for harvesting a mandrake root in relative safety. For example Josephus (c. 37 AD Jerusalem – c. 100) gives the following directions for pulling it up:
A furrow must be dug around the root until its lower part is exposed, then a dog is tied to it, after which the person tying the dog must get away. The dog then endeavours to follow him, and so easily pulls up the root, but dies suddenly instead of his master. After this the root can be handled without fear. (War of Jews - Book 7, Chapter 6 , 3)
(Note: Josephus does not mention the similarity between the Mandrake root and the shape of a man.)
Thus, you will understand the skill necessary of Esau to hunt the "Ish Sadeh", according to the Gra's explanation. If the Dudaim are to be connected with the Mandrake, reputed to be so difficult to "hunt" perhaps this is why they were so highly prized by Rachel.
Also see, the following poem - and it's Midrash ;)