Irvine-based Acorns Grow Inc. won a major endorsement from BlackRock Inc. (NYSE: BLK), the world’s largest asset manager, with $6.3 trillion.

The investment is part of a $50 million fundraising round BlackRock is leading, the Wall Street Journal reported. While the actual amount Blackrock invested wasn’t revealed, the financial giant said in a statement that it’s “an anchor investor and key partner” of Acorns.

Acorns is the country’s fastest-growing micro investing app, with more than 3.3 million investment accounts, BlackRock said. The firms reached an agreement to pursue technology-enabled tools to help the companies participate “among the next generation of investors.”

"Acorns is a pioneer in creating innovative ways to engage investors in a mobile-first world,” said BlackRock Chief Operating Officer Rob Goldstein. “By deepening our understanding of how their customers use investment technologies, we can apply those learnings across BlackRock to evolve the products we build for our distribution partners."

Acorns helps consumers automatically invest spare change from everyday purchases into diversified ETF portfolios.

Local investment banking pioneer Walter Cruttenden and his son Jeffrey launched Acorns in 2014 to bring microinvesting to the masses through a mobile app featuring nominal fees and no minimums.

BlackRock Chief Marketing Officer Frank Cooper will have an observer seat on Acorns’ board of directors.