Rowan is the name of a tree with red berries that's commonly found in Scotland (and said to ward off witches). Some scholars say this name has been used for girls as well as boys since the Middle Ages, though no Rowans are found outside literature until modern times.
In the U.S., Rowan was almost unheard of as a girl's name before Brooke Shields chose it for her daughter in 2003 -- the year that it entered the Top 1000. Now popular for both sexes, there's one girl named Rowan for every two boys.
Rowan Mayfair is a powerful witch in the Anne Rice novel The Witching Hour. A genial Irish surname choice, especially for a redhead -- girl or boy.