Davidson's penstemon vs Penstemon davidsonii

Davidson's penstemon and Penstemon davidsonii both are nouns.

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

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

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

Davidson's penstemon (noun)	Penstemon davidsonii (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