What is the meaning of black-eyed Susan?

noun

• Tropical African climbing plant having yellow flowers with a dark purple center.
  • synonyms: black-eyed Susan vine, Thunbergia alata
• Annual weedy herb with ephemeral yellow purple-eyed flowers; Old World tropics; naturalized as a weed in North America.
  • synonyms: flower-of-an-hour, flowers-of-an-hour, bladder ketmia, Hibiscus trionum
• The state flower of Maryland; of central and southeastern United States; having daisylike flowers with dark centers and yellow to orange rays.
  • synonyms: Rudbeckia hirta, Rudbeckia serotina