water star grass vs Heteranthera dubia

water star grass and Heteranthera dubia both are nouns.

Word	Noun	Adjective	Verb	Adverb
water star grass	Yes	No	No	No
Heteranthera dubia	Yes	No	No	No

As nouns, water star grass and Heteranthera dubia are synonyms defined as:

water star grass and Heteranthera dubia: grassy-leaved North American aquatic plant with yellow star-shaped blossoms

Other synonyms of water star grass include mud plantain.

water star grass (noun)	Heteranthera dubia (noun)
grassy-leaved North American aquatic plant with yellow star-shaped blossoms	grassy-leaved North American aquatic plant with yellow star-shaped blossoms