Pisum arvense vs pea plant

Pisum arvense and pea plant both are nouns.

Word	Noun	Adjective	Verb	Adverb
Pisum arvense	Yes	No	No	No
pea plant	Yes	No	No	No

As nouns, pea plant is a hypernym of Pisum arvense; that is, pea plant is a word with a broader meaning than Pisum arvense:

Pisum arvense: variety of pea plant native to the Mediterranean region and North Africa and widely grown especially for forage
pea plant: a leguminous plant of the genus Pisum with small white flowers and long green pods containing edible green seeds

Other hypernyms of Pisum arvense include pea.

Pisum arvense (noun)	pea plant (noun)
variety of pea plant native to the Mediterranean region and North Africa and widely grown especially for forage	a leguminous plant of the genus Pisum with small white flowers and long green pods containing edible green seeds