Rowan has two convergent origins. The Irish/Scottish surname comes from ruadhán, meaning "little red one" (referring to red hair). The English word "rowan" refers to the rowan tree (mountain ash), considered protective against witches in Celtic and Norse folklore.
Rowan is unisex but increasingly used for girls in the U.S. It entered the top 1000 for girls in 1999 and has been climbing. Today it sits in the U.S. top 200 for girls.
Rowan does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
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In Pythagorean numerology the letters of Rowan reduce to 8, The Visionary. This is a traditional interpretive system, not a factual claim about the name.