Iridaceae, the iris family.
Plant: Yellow flag (or yellow iris) is a showy, introduced member of the iris family with large yellow flowers on sometimes branching stalks rising to 3'. Spreading, it often grows in clumps. Perennial.
Flowers: Bright yellow, 3"-4" wide, with with three large petal-like sepals, sometimes veined with dark red at the base, and three, short, upright petals. Borne severally at the ends of long, sometimes branching stalks. Usually only one flower in a terminal group is open at once.
Leaves: Basal, alternate on stem, linear, swordlike (gladiate), to 3' long.
Fruit: A six-sided, oblong capsule, 1.5"-2" in length, in sparse, terminal clusters.
Habitat: Pond and stream margins, open wet areas.
Introduced from Europe as a garden plant, it has escaped from cultivation.
Occasionally it forms invasive stands.
The "petals" of the irises are actually the sepals, the petals themselves
are small and not very conspicuous.
The roots (actually rhizomes) are emetic and have been used as such
in herbal medicine.
Where to find it:
In park, mainly in one spot, around the pond inlet near the lodge,
though there are a few on southern edge of the pond.