Entwives
From Tolkien Gateway
The mates of the Ents, who had their gardens in the regions later known as the Brown Lands. When Sauron blasted that region, the Entwives escaped into the wilds of Middle-earth and were lost to the Ents (or so the Ents themselves believed).
See also: I found the Entwives! discussion on the where-abouts of the Entwives