upland cotton vs cotton plant

upland cotton and cotton plant both are nouns.

Word	Noun	Adjective	Verb	Adverb
upland cotton	Yes	No	No	No
cotton plant	Yes	No	No	No

As nouns, cotton plant is a hypernym of upland cotton; that is, cotton plant is a word with a broader meaning than upland cotton:

upland cotton: native tropical American plant now cultivated in the United States yielding short-staple cotton
cotton plant: erect bushy mallow plant or small tree bearing bolls containing seeds with many long hairy fibers

Other hypernyms of upland cotton include cotton.

upland cotton (noun)	cotton plant (noun)
native tropical American plant now cultivated in the United States yielding short-staple cotton	erect bushy mallow plant or small tree bearing bolls containing seeds with many long hairy fibers