bristle grass vs bristlegrass

bristle grass and bristlegrass both are nouns.

Word	Noun	Adjective	Verb	Adverb
bristle grass	Yes	No	No	No
bristlegrass	Yes	No	No	No

As nouns, bristle grass and bristlegrass are synonyms defined as:

bristle grass and bristlegrass: grasses of grasslands and woodlands having large gracefully arching spikes with long bristles beneath each spikelet

bristle grass (noun)	bristlegrass (noun)
grasses of grasslands and woodlands having large gracefully arching spikes with long bristles beneath each spikelet	grasses of grasslands and woodlands having large gracefully arching spikes with long bristles beneath each spikelet