What does it look like?
Phragmites is a perennial grass that grows up to 3m tall on water margins. It has bamboo-like stems which carry long, wide, flat leaves that taper to a point. Deciduous, with a period of low activity in autumn and winter. It has large, fluffy, purplish flower heads, and seed grain which is covered in silky hairs.
Prefers margins of still or slow moving water bodies, including fresh and brackish wetlands and drainage ditches. Less salt tolerant than Spartina. Tolerant of fluctuating water levels and can grow away from water. Tolerates mesotrophic to eutrophic water quality, benefits from nutrient addition.
Why is it a problem?
History of invasiveness overseas. Rated as the worst potential aquatic weed in New Zealand. More competitive than Manchurian wild rice. Increased competitiveness in high nutrient environments. Dense litter accumulation leads to low light penetration to ground level, suppressing other plant species. Allelopathic, inhibiting growth of other species.
Vegetative spread locally from creeping rhizomes and can establish from rhizome fragments. Spread along roading corridors overseas known to be an important component of landscape-scale spread. Not known to set seed in New Zealand.