common alder vs Alnus vulgaris

common alder and Alnus vulgaris both are nouns.

Word	Noun	Adjective	Verb	Adverb
common alder	Yes	No	No	No
Alnus vulgaris	Yes	No	No	No

As nouns, common alder and Alnus vulgaris are synonyms defined as:

common alder and Alnus vulgaris: medium-sized tree with brown-black bark and woody fruiting catkins; leaves are hairy beneath

Other synonyms of common alder include Alnus glutinosa, European black alder.

common alder (noun)	Alnus vulgaris (noun)
medium-sized tree with brown-black bark and woody fruiting catkins; leaves are hairy beneath	medium-sized tree with brown-black bark and woody fruiting catkins; leaves are hairy beneath