Ethnobotany. Iris pseudacorus is originally from Europa and Asia but it has been naturalized in many regions of North-America. Many species of Iris – determined ou undetermined –  have been used  by the First Peoples of North America as medicine or as material for survival tools. Daniel Moerman, in his gigantic ethnobotanical corpus, mentioned only one “food” use of Iris among the Eskimos who roast the seeds of Iris setosa to make a beverage the same way the seeds of Iris pseudacorus used to be roasted in Europe for a similar preparation. 

Description by the Glansis. Identification: Iris pseudacorus is a perennial, emergent aquatic plant ranging from 0.5–1.5 m in height (Campbell et al. 2010, Forest Health Staff 2006). Its inflorescence units consist of 4–12 flowers per stem; 6–9 cm spathes are green with brown margins. The outer spathe is strongly keeled, while the inner is without keel; they are subequal and the margins are not dry or membranous. Bright yellow flowers are approximately 7–9 cm wide and occasionally have brown/purple veins at the base of lanceolate to spatulate petals (Lui et al. 2010, Noxious Weed Control Program 2009). Each flower has three downward sepals (5–7.5 cm by 3–4 cm) and three upward petals (2–3 cm) and a floral tube 0.6–0.8 cm (Lui et al. 2010). Flowers typically bloom from April-June (Forest Health Staff 2006). Fruit are prismatic, 6-angled, glossy green capsules (3.5–8.5 cm); individual plants may produce up to 6 pods (Campbell et al. 2010, Jacobs et al 2011). Each capsule may release up to 120 lustrous brown, flattened, D-shaped seeds (6–7 mm), but a small fraction of these are actually viable (Campbell et al. 2010, Jacobs et al. 2011). The corky seeds are buoyant, with 95% of them able to float for up to 2 months (Forest Health Staff 2006, Jacobs et al. 2011, Lui et al. 2010, Noxious Weed Control Program 2009).
The basal deciduous leaves are smooth, stiff, broad, dark green with a gray/blue cast and have a central ridge (40–100 cm by 2–3 cm) (Forest Health Staff 2006, Lui et al. 2010). Stems are usually solid, unbranched, and 70–150 cm in length (Lui et al. 2010). The plant remains green during mild winters (Noxious Weed Control Program 2009).

The fleshy roots are about 10–30 cm long (Lui et al. 2010). This species also has numerous, thick, pink tuberous rhizomes (2–3 cm in diameter) that are freely branching and may form extensive clumps (Noxious Weed Control Program 2009). If broken, rhizomes release black sap (Jacobs et al. 2011).

When not in bloom, it can be difficult to distinguish I. pseudacorus from native irises (Lui et al. 2010, Sarver et al. 2008). It can be distinguished from Northern blue flag iris, which has a three-angled seed capsule (yellow iris has a six-angled capsule) (Campbell et al. 2010). When in bloom, it is easy to distinguish because it is the only iris that grows completely yellow in natural environments (Goodridge et al. 2011).

Materia Medica. Iris pseudacorus has been a major plant in the pharmacopia of the traditional European herbalists such as Culpeper and Gerard. « The Yellow Flag rhizome was formerly much employed as a medicine, acting as a very powerful cathartic, but from its extremely acrid nature is now seldom used. An infusion of it has been found to be effective in checking diarrhoea, and it is reputed of value in dysmenorrhoea and leucorrhoea » in “A modern Herbal” by Grieve.  

According to Stephen Harod Buhner in “Sacred Beers”: «Orris is made from the roots of any of the three Iris species: Iris germanica, Iris florentina or Iris pallida. The fresh roots, as with so many iris family members, are actively irritant. Upon drying, this quality is lost and the roots of iris species are used in herbal medicine in much the same way. Primarily, they are a gastric, bill and gastric enzyme stimulant. They also possess diuretic and expectorant qualities. Strong in their action, they are usually used with other herbs that soften their impact on the system. Orris roots, possessing a wonderful fragrance, are now most commonly used as an additive and in perfumes and bath salts. The primarily iris, used in herbal medicine, is the American Blue Flag, or wild iris, Iris missouriensis.»