portulaca vs rose moss

portulaca and rose moss both are nouns.

Word	Noun	Adjective	Verb	Adverb
portulaca	Yes	No	No	No
rose moss	Yes	No	No	No

As nouns, rose moss is a hyponym of portulaca; that is, rose moss is a word with a more specific, narrower meaning than portulaca:

portulaca: a plant of the genus Portulaca having pink or red or purple or white ephemeral flowers
rose moss: widely cultivated in many varieties for its fleshy moss-like foliage and profusion of brightly colored flowers

Other hyponyms of portulaca include Portulaca grandiflora, sun plant.

portulaca (noun)	rose moss (noun)
a plant of the genus Portulaca having pink or red or purple or white ephemeral flowers	widely cultivated in many varieties for its fleshy moss-like foliage and profusion of brightly colored flowers