casuarina vs she-oak

casuarina and she-oak both are nouns.

Word	Noun	Adjective	Verb	Adverb
casuarina	Yes	No	No	No
she-oak	Yes	No	No	No

As nouns, she-oak is a hyponym of casuarina; that is, she-oak is a word with a more specific, narrower meaning than casuarina:

casuarina: any of various trees and shrubs of the genus Casuarina having jointed stems and whorls of scalelike leaves; some yield heavy hardwood
she-oak: any of several Australian trees of the genus Casuarina

Other hyponyms of casuarina include beefwood.

casuarina (noun)	she-oak (noun)
any of various trees and shrubs of the genus Casuarina having jointed stems and whorls of scalelike leaves; some yield heavy hardwood	any of several Australian trees of the genus Casuarina