Flag root at English => English (Websters 1913) Of Explained:
Flag \Flag\, n. [From {Flag} to hang loose, to bend down.]
(Bot.)
An aquatic plant, with long, ensiform leaves, belonging to
either of the genera {Iris} and {Acorus}.
{Cooper's flag}, the cat-tail ({Typha latifolia}), the long
leaves of which are placed between the staves of barrels
to make the latter water-tight.
{Corn flag}. See under 2d {Corn}.
{Flag broom}, a coarse of broom, originally made of flags or
rushes.
{Flag root}, the root of the sweet flag.
{Sweet flag}. See {Calamus}, n., 2.