Britain's only large native yellow iris, of pond margins and wet woods, with falls that hang and tiny erect standards
Yellow flag — Iris pseudacorus.
Nature · Wildflowers & flowers
Yellow flag iris
Flowers May to August
Iris pseudacorus — Iridaceae
The yellow flag is Britain's only large native yellow iris, a stout plant of pond margins, river banks, fens, wet woods and saltmarsh, with grey-green sword leaves and bright yellow flowers whose outer segments hang down. Its epithet means "false Acorus", because out of flower it is easily taken for sweet flag. It is a strong candidate for the original of the heraldic fleur-de-lis, and it is widely planted in reed beds to strip nutrients and metals from water.
How to spot them
- ▸Flowers bright yellow, 8–10 cm across, the three outer falls hanging down with faint brown or violet veining
- ▸Three narrow, erect inner standards, much smaller than the falls, and three flat style branches
- ▸Sword-shaped grey-green leaves in flat fans, with a raised midrib, to over a metre
- ▸Wet ground: the margins of ponds, ditches, rivers, fens, wet woodland and brackish marsh, May to August
- ▸Large three-angled seed capsules holding flat, corky, brown seeds that float
How to know it
Its epithet means 'false Acorus', because out of flower it is taken for sweet flag
Iris pseudacorus — sweet flag, Acorus calamus, has a crimped leaf edge and a tangerine scent.
Often named as the original of the heraldic device borne by the kings of France
The fleur-de-lis, usually traced to the yellow flag iris.
Planted in constructed wetlands because its roots strip nutrients and heavy metals out of water
Yellow flag — Iris pseudacorus.
Its genus is named for the Greek goddess of the rainbow, and its roasted seeds were once a coffee substitute
Iris pseudacorus, the yellow flag; its rhizome also gave a black dye and ink.
County flower of Wigtownshire; a serious invasive weed of waterways in North America and New Zealand
Yellow flag.
Its flat corky seeds float, so colonies spread downstream along rivers and ditches
Yellow flag.
Quick-fire facts
- •Family Iridaceae; pseudacorus means false Acorus, after the sweet flag, Acorus calamus
- •Iris is named for the Greek goddess of the rainbow
- •The Wildlife Trusts give a height of 40–100 cm, a flowering season of May to August, and note that it can be invasive in small ponds
- •The only other native British iris is the stinking iris, Iris foetidissima, which has dull purple flowers and orange seeds
- •Widely used in phytoremediation and constructed wetlands, because the rhizomes take up metals and nutrients
- •County flower of Wigtownshire in Plantlife's 2002 County Flowers survey
- •Listed as a noxious or invasive weed in parts of the United States and in New Zealand, where it chokes waterways
- •The rhizome is poisonous and the sap can irritate the skin; it yielded a black dye and, with iron, a writing ink
Drill it — 8 cards
1 / 8new card
Sources
- The Wildlife Trusts — Yellow iris