There are two Hebrew words rendered "flag" in our Bible:

1. A word of Egyptian origin, and denoting "any green and course herbage, such as rushes and reeds, which grows in marshy places." ( Genesis 41:2 Genesis 41:18 ) (here translated meadow). It is perhaps the Cyperus esculentus .
2. A word which appears to be used in a very wide sense to denote "weeds of any kind." ( Exodus 2:3 Exodus 2:5 ; Isaiah 19:6 )