field speedwell vs speedwell

field speedwell and speedwell both are nouns.

Word	Noun	Adjective	Verb	Adverb
field speedwell	Yes	No	No	No
speedwell	Yes	No	No	No

As nouns, speedwell is a hypernym of field speedwell; that is, speedwell is a word with a broader meaning than field speedwell:

field speedwell: European plant with minute axillary blue flowers on long stalks; widely naturalized in America
speedwell: any plant of the genus Veronica

Other hypernyms of field speedwell include veronica.

field speedwell (noun)	speedwell (noun)
European plant with minute axillary blue flowers on long stalks; widely naturalized in America	any plant of the genus Veronica