Yarrow is a feathery white-and-pink wildflower long valued in folk healing, from the Old English gearwe.
Yarrow 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 Yarrow reduce to 1, The Leader. This is a traditional interpretive system, not a factual claim about the name.