black-eyed susan has 8 distinct synonyms spread across 3 of its 3 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
tropical African climbing plant having yellow flowers with a dark purple center
annual weedy herb with ephemeral yellow purple-eyed flowers; Old World tropics; naturalized as a weed in North America
the state flower of Maryland; of central and southeastern United States; having daisylike flowers with dark centers and yellow to orange rays
Synonyms, antonyms and the broader and narrower relations for black-eyed susan come from Princeton University’s WordNet. Full sources and licences.