If a peep who lives in town gave you a seed called "Blackberry Ananas" during exchange of favors, it's a flower and you can enjoy it as such or donate it to the museum. Since you said "blackberry" I assumed that was part of the name. The peeps won't eat it since they prefer apples, pears, and oranges. As Barbara the Unicorn said, there are also conditions where you might get various items (including flowers) as part of a quest and you need to find out who wants the item.

I'm still clueless as to how hybrids are bred but I plant my flowers in a pattern that puts dissimilar plants next to each other left to right, with some space front and back so hybrids can spawn. I've gotten Daisy Lemongrass and Blue Flower something that way.

BTW, although a peep did give me a rare seed once-and-only-once, my peeps generally seem to think the mayor needs a HUGE lemon maranta garden, based on what they give me for favors. Pah.