Encountered it in George R. R. Martin's A Song of Ice and Fire (Melantha Stark née Blackwood) and it's so alluring and mysterious! Both dark (melas-) and honey (meli-) are pretty affixes to anthos.
The name is not English, it is Greek, very ancient. It consists of 'mel', meaning 'dark', and 'antha', meaning 'flower': thus Melantha means 'Dark Flower'. This has two references: either to a girl with dark hair and eyes, OR to a girl with a dark side to her personality.
"Melantha" might be a variant of the Greek name "Melantho" (accent on the "a") which appears in the epic poem "The Odyssey," and its masculine form, "Melanthios," which also appears here.
That's a shame because I think the meaning of this name could mean "sweet flower" or "dark flower" because the 'Mel' part of Melantha could be related to honey like "Melissa" means bee in Greek or it could be related to 'dark' like Melanie.
https://www.behindthename.com/name/melissa
https://www.behindthename.com/name/melanie
https://www.names.org/n/melantha/about
https://www.nancy.cc/baby-name/melantha/
https://www.popular-babynames.com/name/melantha
https://forebears.io/forenames/melantha