hardstemmed bulrush vs hardstem bulrush

hardstemmed bulrush and hardstem bulrush both are nouns.

Word	Noun	Adjective	Verb	Adverb
hardstemmed bulrush	Yes	No	No	No
hardstem bulrush	Yes	No	No	No

As nouns, hardstemmed bulrush and hardstem bulrush are synonyms defined as:

hardstemmed bulrush and hardstem bulrush: widely distributed North American sedge having rigid olive green stems

Other synonyms of hardstemmed bulrush include Scirpus acutus.

hardstemmed bulrush (noun)	hardstem bulrush (noun)
widely distributed North American sedge having rigid olive green stems	widely distributed North American sedge having rigid olive green stems