prickly pear vs prickly pear cactus

prickly pear and prickly pear cactus both are nouns.

Word	Noun	Adjective	Verb	Adverb
prickly pear	Yes	No	No	No
prickly pear cactus	Yes	No	No	No

As nouns, prickly pear and prickly pear cactus are synonyms defined as:

prickly pear and prickly pear cactus: cacti having spiny flat joints and oval fruit that is edible in some species; often used as food for stock

prickly pear (noun)	prickly pear cactus (noun)
round or pear-shaped spiny fruit of any of various prickly pear cacti	cacti having spiny flat joints and oval fruit that is edible in some species; often used as food for stock
cacti having spiny flat joints and oval fruit that is edible in some species; often used as food for stock