Juglans californica vs walnut

Juglans californica and walnut both are nouns.

Word	Noun	Adjective	Verb	Adverb
Juglans californica	Yes	No	No	No
walnut	Yes	No	No	No

As nouns, walnut is a hypernym of Juglans californica; that is, walnut is a word with a broader meaning than Juglans californica:

Juglans californica: medium-sized tree with somewhat aromatic compound leaves and edible nuts
walnut: any of various trees of the genus Juglans

Other hypernyms of Juglans californica include walnut tree.

Juglans californica (noun)	walnut (noun)
medium-sized tree with somewhat aromatic compound leaves and edible nuts	nut of any of various walnut trees having a wrinkled two-lobed seed with a hard shell
	any of various trees of the genus Juglans
	hard dark-brown wood of any of various walnut trees; used especially for furniture and paneling