sweet clover vs ligneous plant

sweet clover and ligneous plant both are nouns.

Word	Noun	Adjective	Verb	Adverb
sweet clover	Yes	No	No	No
ligneous plant	Yes	No	No	No

As nouns, ligneous plant is a hypernym of sweet clover; that is, ligneous plant is a word with a broader meaning than sweet clover:

sweet clover: erect annual or biennial plant grown extensively especially for hay and soil improvement
ligneous plant: a plant having hard lignified tissues or woody parts especially stems

Other hypernyms of sweet clover include woody plant.

sweet clover (noun)	ligneous plant (noun)
erect annual or biennial plant grown extensively especially for hay and soil improvement	a plant having hard lignified tissues or woody parts especially stems