Mystery Sender of Cardi B's 'Tom Petty' Flowers Revealed

Cardi B did not get flowers from the great beyond -- as she insinuated by thanking Tom Petty for a Grammys bouquet she received -- but, TMZ has learned who REALLY did the honors.

Sources tell us ... celebrity florist Annie Wonderlich, owner of Art Fleur, sent the bouquet wishing Cardi luck at the award show. We're told Cardi is one of her clients, and Annie also delivered a Grammy arrangement to Lady Gaga.

After getting the flowers, Cardi looked at the back of the card -- which contained a Petty lyric -- and thought they were from him. She thanked Tom on social media ... prompting the internet to quickly point out that would be pretty freakin' amazing (as in, impossible) since TP sadly died nearly 2 years ago.

Although, we're sure Ghost Tom's probably a Bardi fan.

The sender's true identity was there the whole time ... because the other side of the card had a note from Annie reading, "Cardi B! Wishing you LOVE, LIGHT & LUCK tonight at the Grammys! All the best! XOXO, The Art Fleur Team."

We're told Annie's company has TONS of celeb clients, including Kim Kardashian and Taylor Swift, and every special delivery comes with a card quoting someone famous -- like Oscar Wilde, Claude Monet, David Bowie, and in this instance, Petty.

As for the flowers ... we're told the $600 arrangement is dubbed "Ms. B" and stands 3 and a half feet tall!!! There are 250 vendulas, orange crush and garden roses ... and monster leaves painted with 24-karat gold!!!