rhubarb vs genus Rheum

rhubarb and genus Rheum both are nouns.

Word	Noun	Adjective	Verb	Adverb
rhubarb	Yes	No	No	No
genus Rheum	Yes	No	No	No

rhubarb (noun)	genus Rheum (noun)
long pinkish sour leafstalks usually eaten cooked and sweetened	rhubarb
plants having long green or reddish acidic leafstalks growing in basal clumps; stems (and only the stems) are edible when cooked; leaves are poisonous