yellow flag vs Iris pseudacorus

yellow flag and Iris pseudacorus both are nouns.

Word	Noun	Adjective	Verb	Adverb
yellow flag	Yes	No	No	No
Iris pseudacorus	Yes	No	No	No

As nouns, yellow flag and Iris pseudacorus are synonyms defined as:

yellow flag and Iris pseudacorus: common yellow-flowered iris of Europe and North Africa, naturalized in United States and often cultivated

Other synonyms of yellow flag include yellow iris, yellow water flag.

yellow flag (noun)	Iris pseudacorus (noun)
common yellow-flowered iris of Europe and North Africa, naturalized in United States and often cultivated	common yellow-flowered iris of Europe and North Africa, naturalized in United States and often cultivated