Some similarities to : Daffodils, but daffodils don't grow in water or have three large petals flopping down.

Uniquely identifiable characteristics: There is no other plant quite like this.

Distinguishing Feature : The large yellow petals in triplets at 120 degrees. Always grows in water.

Like many aquatic plants, this too has petals in three's.

The poisonous cardiac glycoside Iridin (aka Irisin) is found in the leaves and rhizomes of Yellow Iris. If ingested symptoms include nausea, elevated temperature, vomiting, abdominal pain, severe purgation can result. It is dangerous to animals. Most irises contain this substance. It is also found in the roots of the Violet Family.

Yellow Iris spreads underwater by thick rhizomes in anoxic conditions, and is able to withstand quite acidic conditions (low pH - below 7). It is a Metallophyte and selectively absorbs heavy metals and has been used to help clean up heavy metal pollution, provided that pollution occurs in water - for Yellow Iris needs wet conditions and will not grow on dry land.

The rhizomes were once used to produce both a black dye and an ink.

Yellow Flag is a perennial with stout stems and an under-ground horizontal tuber. It is poisonous.

Irisquinone is a contact allergen found in Yellow Flag, which is very similar to one of the quinones (Primin) found in species of Primrose, some species of which are notoriously allergenic, causing contact dermatitis. Compare with GeranylGeranyl-Benzoquinone and other benzoquinones with long aliphatic side chains.