finger grass vs genus Digitaria

finger grass and genus Digitaria both are nouns.

Word	Noun	Adjective	Verb	Adverb
finger grass	Yes	No	No	No
genus Digitaria	Yes	No	No	No

finger grass (noun)	genus Digitaria (noun)
any grass of the genus Chloris; occurs in short grassland especially on waste ground or poor soils	crab grass; finger grass
grasses with creeping stems that root freely; a pest in lawns