And the winner is...

Jenn! At least, she came closest in her guess. The mystery object is not a hybrid vegetable, but actually an heirloom broccoli variety called Romanesco. I picked it up at the Co-op last weekend because it was so curious-looking and it turned out I like it a little better than the old garden-variety (yuk yuk) broccoli. It's a little milder, and delicious steamed.