Who is the Greek goddess of flowers in autumn?
the goddess of springtime (therefore all flowers) is Persephone, Hades' wife
Her name was Flora in Roman Mythology. Words such as "floral" and other words and names that use the Latin root word "flora," are derived from the name of the Roman goddess of flowers. Additional note, for Greek Mythology: Demeter is the Greek goddess of vegetation and fruitfulness (the harvest), so she might also be the goddess of flowers in Greek Mythology.
Persephone is indeed the goddess of flowers. She is only the goddess of flowers and the reason is clear- she was kidnapped by Hades, the greek god of the Underworld and forced to be his wife. I feel sorry for Persophone because I wouldn't want a husband known for bringing people to their death to the underworld.