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Yellow Flag

Iris pseudacorus

The Yellow Flag is one of the most attractive marsh plants of the Donau-Auen National Park. Flowering from May to June, its large, brilliant yellow flowers stand out in the reed beds of wet places, easily outshining other "wallflowers" such as the Common Reed or Reed mace, which have far less spectacular brown or greenish blossoms.

Description
Reaching a height of up to 1m, the Yellow Flag is the largest native iris by far. Its long, sword-shaped leaves are 1-3cm wide and have a prominent raised midrib. The leaves are grass-green and almost as long as the flattened stem. Only the base of the leaves has a purplish colouring. The brilliant flowers have three inside and three outside petals. The oblong outer petals are drooping; these fall petals are supported by a green spathe. The narrower inner petals are stiffly erect and are dominated by the wide, petal-like stigma. After pollination large three-parted capsules with a roughly triangular shape are formed; they droop heavily. Inside the capsule, the orange-brown seeds are arranged like pieces of maize; seeds can float.

Distribution
The species occurs throughout most of Europe, in parts of Asia and northwest Africa. The Yellow Flag is found only locally in Austria but in all provinces. It prefers warmer sites and may only be found below montane zones. Typical sites include wet, periodically flooded soils. Iris pseudacorus is most likely found in Alder groves, White Willow riparian forests, marshes, water ditches and on the banks of slowly-moving waters. In the Donau-Auen National Park it is commonly occurring.

Endangerment and Conservation Status
Yellow Flag is regionally vulnerable, e.g. in Alpine areas and in the so-called "Bohemian formation", a geological zone comprising parts of Czech Republic, Upper Bavaria and Lower Austria. All species of the iris are fully protected in Lower Austria and partly protected in Vienna.

Ecological Characteristics
The Yellow Flag has adapted optimally to its amphibian habitat. Large pockets of air found within its green leaves provide oxygen to the plant's creeping stems burrowing in the airless mud. Its long sturdy stem lifts the flowers above water, even at high water; its ripe seeds have air-filled cavities which enable them to float. The three-parted iris flowers are also highly functional. A tube-shaped unit is formed by the stamen, the style, and the three outer fall petals which have faint brown markings. A pollinating insect searching for nectar hidden in the corolla must literally brush past the stamen and style to get to it.

Special Characteristics
Its scientific name derives from this species' similarity with the Sweet Flag, or Acorus calamus, which often grows at the same sites. The aromatic rootstock of Sweet Flag was used in antiquity to stimulate the appetite and as an anti-inflammatory cure for stomach ailments. In contrast, the rhizome of the Yellow Flag is not aromatic at all and is in fact slightly toxic due to its pungent-tasting tannins. Yet it has been traditionally used as a cure-all for stomach ailments in popular medicine.

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