Giant reed
Arundo donax
Family · Poaceae · Harmless
The reed bed that takes over every southern stream and that almost everyone assumes is native. It is not: it came from Asia, lets nothing else grow, and is among the country's worst riparian invaders.
Streams and ditches · Roadsides and waste ground · Fields and pasture
Also known asgiant cane, Spanish cane
How to tell it
Hollow canes several metres tall with clear nodes and broad alternate leaves. A feathery panicle in late summer. It grows in impenetrable stands, always by water.
What it is confused with
Common reed
Phragmites australis
Common reed is native, thinner and flexible, with a silky dark panicle; giant reed is thick, rigid and much broader-leaved. Worth knowing the difference: one is to protect, the other to remove.
What it is for
Fishing rods, thatch, roofing and woodwind reeds, a use that continues. None of it makes up for what it does to streams: it raises flood risk and replaces willow and alder.
The law says
An invasive alien species in Portugal. Do not plant or propagate it, and cutting without removing the rhizome multiplies it.