Hortensia comes from the Roman family name Hortensius — from the Latin hortus, meaning "garden." The hydrangea flower is called hortensia in many languages, named for an 18th-century French botanist's wife.
Hortensia is rare in English but used in France, Spain, and Latin America.
Hortensia 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.
In Pythagorean numerology the letters of Hortensia reduce to 1, The Leader. This is a traditional interpretive system, not a factual claim about the name.