Penstemon davidsonii vs Davidson's penstemon

Penstemon davidsonii and Davidson's penstemon both are nouns.

Word	Noun	Adjective	Verb	Adverb
Penstemon davidsonii	Yes	No	No	No
Davidson's penstemon	Yes	No	No	No

As nouns, Penstemon davidsonii and Davidson's penstemon are synonyms defined as:

Penstemon davidsonii and Davidson's penstemon: mat-forming plant with blue and lavender flowers clustered on short erect stems; British Columbia to northern California

Penstemon davidsonii (noun)	Davidson's penstemon (noun)
mat-forming plant with blue and lavender flowers clustered on short erect stems; British Columbia to northern California	mat-forming plant with blue and lavender flowers clustered on short erect stems; British Columbia to northern California