Rowan draws on two related threads: the Irish ruadh, "little red one," and the rowan tree itself, long used in folk tradition to ward off harm. Together they give the name a protective undertone, paired with a warmth suggested by its color association.
If possible, the planets must be reinforced with a fixed star from the same nature, because it concentrates the power of the influx and the duration of the work. - Picatrix (Andalusia, ~1000.AD)