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Yellow iris: a botanical bully

June 30, 2009
By Hilary Smith,

A silent invasion is underfoot. By root. By foot. By fin. Invasive plants and animals are floating, flying, swimming and otherwise hitching rides to new places. These organisms are not native to the Adirondacks. Taking up residence here, they wreak havoc on our rivers, lakes, wetlands and woods. Fisheries, forestry, agriculture and recreation all suffer from the consequences of invasive species.

Some invaders are already here - like the invasive aquatic plant Eurasian watermilfoil. Others - such as emerald ash borer, a forest pest - are on their way. Because they are outside their native range, invasives have no natural predators to keep populations in check. But we can stop their spread.

Invasive species often go un-noticed until they are already well established and not much can be done. We can change that by learning to recognize them, their signs and their symptoms. Finding invasives early boosts the chance of successfully controlling an infestation and, hopefully, eradicating it altogether.

Article Photos

Yellow iris
(Photo provided)

Summer is a great time to be on the lookout for invading plants and animals. Sometimes they can be tricky to distinguish from their native look-alikes; the good news is that we are here to help. I am part of a team at the Adirondack Park Invasive Plant Program (APIPP). My colleagues Steven Flint, who focuses on terrestrial invasives, Tyler Smith, who focuses on aquatics, and I work with communities and organizations across the region to shut the door on invasive species.

The invader on the scene this week is yellow iris (Iris pseudacorus). Blooming in June, it surely is a pretty plant, but do not let its good looks fool you. Often called the "botanical bully," yellow iris is an aggressive spreader - and poisonous, too. Its roots, or rhizomes, can connect hundreds of flowering plants, choking native wetland plants, restricting water flow and degrading habitat for fish, plants and other animals.

Introduced as an ornamental plant from Europe and the Mediterranean region, yellow iris escaped the garden. This perennial was reported in the Hudson River drainage near Poughkeepsie in 1868 and has since spread across most of the United States. Edges of lakes, ponds, rivers and streams provide prime habitat, and its seeds can spread long distances along these watery routes.

The brilliant yellow flower is key to its identification; otherwise, it looks similar to native cattail and blue flag iris. The plant grows 3 to 4 feet with broad, sword-shaped leaves that are stiff, erect and green with a grayish-blue cast. Yellow iris tolerates drought, acidity and low-oxygen soils, further enabling it to compete. Populations can form large, dense monocultures.

Care should be taken when removing this plant - resins in the leaves and rhizomes can irritate the skin. Plus, any roots remaining in the ground can grow new infestations. Before beginning any control program, verify the plant's identification and proper treatment techniques.

Though still limited in the Adirondack region, yellow iris is spreading. Keep an eye out for this Adirondack invader in gardens, ornamental ponds, wetlands and riverbeds.

Citizens are stepping up to help stamp out yellow iris and other invasives during the 4th annual Adirondack Invasive Species Awareness Week, July 5-11. Check out the lineup of activities in your community online at


Eye on Invasives is a biweekly column that spotlights a top invader when it is easiest to identify. Hilary Smith directs the Adirondack Park Invasive Plant Program, a partnership program housed at the Adirondack Chapter of The Nature Conservancy in Keene Valley, NY. Find out more about this award-winning program online at



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