Weed Department
Idaho State Noxious 
Weed Law
Giant Salvinia


Giant knotweed is an herbaceous perennial, strongly rhizomatous, growing over 12 feet tall. It has huge elephant-ear shaped leaves. It is similar to Japanese knotweed but its features are larger in size.

Flower Description: Flowers are white with a greenish tint and are in small clusters (panicles) in the leaf axils mainly on the upper portions of the stems.

Leaf Description: Leaves are alternate, very large and heart shaped. They are often more than a foot long and 2/3 as wide.

Stem Description: Stems are hollow, jointed and swollen at the nodes.

Fruit/Seed Description: The seed structure is a 3-sided achene that is shiny and brown-black.


Interesting Facts:

It creates dense colonies that exclude native vegetation and greatly alter natural ecosystems. Established populations are extremely persistent and difficult to eradicate, even very small fragments can form new plants.