The Middle English version of the poem derives from an Old French "aristocratic" version but differs somewhat in details. The opening section concerning how the two are born is missing from the English versions. Originally it dates to around 1250 and was called Floris and Blanchefleur.
Floris ("belonging to the flower") and Blanchefleur ("white flower") are raised together at the court and grow close. King Fenix fears his son may desire to marry the "pagan" girl and decides that she must be killed. However, he cannot bring himself to do the act and instead sends Floris away to school, then sells Blanchefleur to merchants traveling on the way to Cairo (called Babylon in the story), where she is then sold to the emir. Fenix constructs an elaborate tomb for Blanchefleur and tells Floris she has died. Floris's reaction is so severe that Fenix tells him the truth. Distraught but encouraged she is still alive, Floris sets out to find her.
Floris eventually arrives outside Cairo where he meets the bridge warden named Daire who tells him about the emir's tower of maidens. Each year the emir selects a new bride from his tower and kills his old wife. Rumour has it that Blanchefleur is soon to be his next chosen bride. To gain access to the tower, Daire advises Floris to play chess with the tower watchman, returning all winnings to him until the watchman is forced to return the favor by allowing him entrance to the tower. Floris outplays the watchmen at chess, and according to plan, Floris is smuggled in to the tower in a basket of flowers, but is mistakenly placed in the room of Blanchefleur's friend Claris. Claris arranges a reunion between the two, but they are discovered two weeks later by the emir.
The emir holds off killing them on the spot until he holds a council of advisers. So impressed are the advisers at the willingness of the young lovers to die for one another that they persuade the emir to spare their lives. Floris is then knighted, he and Blanchefleur are married, and Claris marries the emir (who promises Claris she will be his last and only wife, forever). Soon after, news of Fenix's death reaches Cairo and Floris and Blanchefleur depart for home where they inherit the kingdom, embrace Christianity, and convert the subjects as well.
Blancheflour is in a different caliphate from Flores, and there she is accused falsely and sent as a slave to a Tower of Maidens. The Emir has within his garden a "Tree of Love" that determines a new wife for him every year. Its flower will fall on the destined maiden from the harem, and yet he can also magically manipulate the tree to cast its flower upon a favorite. He has decided to make it fall on Blancheflour, for she is the loveliest virgin in the harem. Flores, knowing that Blancheflour is about to be taken by the Emir for wife, comes to rescue her from her peril. The reunited lovers are found in bed (though they were chastely together) by the Emir the next morning. When he hears their whole tale of chaste love and long promises to one another, he demands proof of her virginity by having her put her hands in a water that will stain if she has been with a man. She is proven pure, he pardons both lovers, and all is well.
The Middle English version of the poem derives from an Old French "aristocratic" version (Floire et Blancheflor) of the tale. The story has analogs in Indian literature, particularly the Jatakas of the early fifth century. Many of the details, such as the Tower of Maidens (i.e. harem), eunuch guards, and the odalisques derive from material carried to the west via The Arabian Nights. The tale could be originally French, or possibly of Oriental origins, or a synthesis of motifs.
Boccaccio tells a version of the same tale in his "Filocolo" in the Decameron. The tale has been a popular subject for later retellings, and it was treated by Swedish poet Oskar Levertin in the romantic ballad "Flores och Blanzeflor" in the collection Legender och visor (Legends and Songs) in 1891.