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A rhizomatous perennial of the Iridaceae family, the yellow flag iris is native to Europe, North Africa, and Western Asia. It is one of the few species of the genus to colonize aquatic and semi-aquatic environments: riverbanks, reed beds, ditches, marshes, ponds, and floodplains, from sea level up to about 1,500 meters in the mountains.
It forms large vigorous clumps of 80 to 150 cm, with erect foliage, in flat blades of bright green, which persist for much of the year. The flowers are a bright and vivid yellow, with widely spread falls bearing characteristic orange-brown veins on their central part, which immediately distinguishes them from other cultivated yellow irises.
In its natural habitat, its flowering extends from May to July depending on latitude and altitude. In cultivation, it generally occurs in May-June.
Its name pseudacorus, meaning "false acorus," recalls the resemblance of its foliage to that of Acorus calamus. The plant is toxic to domestic animals. Its seeds, once roasted, were said to have been used as a coffee substitute. It is considered an invasive species in several regions of North America where it has been introduced.
In cultivation, it thrives in fresh to moist soil, in full sun or partial shade, at the edge of a body of water or in open ground. It adapts well to pot culture, in a substrate kept regularly moist, and proves more resistant to temporary drought than generally supposed. Its vigor is such that it can quickly colonize an area; regular division of clumps is advised.