The name given to a variety of tall plant that grows thickly on open or disturbed ground (the Bonfire Glade in the Old Forest was an ideal habitat for them, and indeed Frodo and his companions found hemlocks growing thickly there). They were also found in the woods of Doriath during the First Age, and especially in the glade in the Forest of Neldoreth where Beren first came upon Lúthien. In his song of their story, Aragorn tells of 'hemlock-umbels', which are the flowers of the hemlock (or, properly, the tightly packed clusters of many small individual flowers that are a distinctive feature of hemlocks and their relatives).