hardstem bulrush vs hardstemmed bulrush

hardstem bulrush and hardstemmed bulrush both are nouns.

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

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

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

Other synonyms of hardstem bulrush include Scirpus acutus.

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