Here's a buzzkill for Starbuds Flowers ... Starbucks is taking the mobile marijuana biz to court and claiming it's ripping off the coffee brand's famous logo.

According to new legal docs, obtained by TMZ, Starbucks is suing Starbuds for trademark infringement. Starbucks says Starbuds, which sells weed out of a converted food truck in New York City, is deliberately copying the iconic siren design logo.

It doesn't take a legal expert to see the similarities here ... but Starbucks goes ahead and lays it all out in their suit, claiming Starbuds' logo straight up jacked the double-ringed green circle and crown-wearing mermaid from their coffee brand, even using the same proportions.

In the suit, Starbucks claims Starbuds is clearly intending to copy its brand with a similarly confusing logo and name ... and the coffee giant says it's been trying to stop Starbuds from using the imagery, to no avail.

Starbucks isn't just pissed about the logo on the weed truck ... the corporation also claims Starbuds is slapping the images on pre-roll joints and other marijuana products.

In the suit, Starbucks claims Starbuds is trying to make money off their longstanding brand recognition ... confusing consumers in the process.

Starbucks wants a court to order Starbuds to stop using the logo and destroy any products that already have it ... and to make Starbuds cough up any profits it's made off the logo.