A perennial herb, yellow iris (Iris pseudacorus) is native to Europe, western Asia, and northern Africa. It was probably imported for gardens. It has long, thin leaves and bright yellow flowers, and grows from 1.5 to 4 feet tall.
It invades wetlands, sending out rhizomes (underground stems) to form dense colonies that displace native species.
You can remove small numbers of plants by hand; be sure to extract the entire rhizome. Repeated cutting can keep populations controlled and prevent seed production. Systemic herbicides based on the active ingredient glyphosate are effective when applied directly to cut stems or as a foliar spray. Yellow iris typically grows in wetlands, where control is subject to the Massachusetts Wetlands Protection Act; be sure to check with the local conservation commission before taking action. Always read and follow the directions on the label when using herbicides. In wetlands, only apply herbicides registered for use in these habitats.