Sium vs rosid dicot genus

Sium and rosid dicot genus both are nouns.

Word	Noun	Adjective	Verb	Adverb
Sium	Yes	No	No	No
rosid dicot genus	Yes	No	No	No

As nouns, rosid dicot genus is a hypernym of Sium; that is, rosid dicot genus is a word with a broader meaning than Sium:

Sium: perennial of wet and marshy places in the Northern Hemisphere: water parsnips
rosid dicot genus: a genus of dicotyledonous plants

Sium (noun)	rosid dicot genus (noun)
perennial of wet and marshy places in the Northern Hemisphere: water parsnips	a genus of dicotyledonous plants