pollen vs pollinium

pollen and pollinium both are nouns.

Word	Noun	Adjective	Verb	Adverb
pollen	Yes	No	No	No
pollinium	Yes	No	No	No

As nouns, pollinium is a hyponym of pollen; that is, pollinium is a word with a more specific, narrower meaning than pollen:

pollen: the fine spores that contain male gametes and that are borne by an anther in a flowering plant
pollinium: a coherent mass of pollen grains (as in orchids)

Other hyponyms of pollen include ragweed pollen.

pollen (noun)	pollinium (noun)
the fine spores that contain male gametes and that are borne by an anther in a flowering plant	a coherent mass of pollen grains (as in orchids)