Doubting it's the sepal. The sepal is the casing around a flower, like the nanner or the calyx. That 'spikey' thing is a different structure altogether, but I still haven't found out what it is. Next time I get one, I'll follow it back to it's base, and see if maybe it's a growing tip poking through the calyxs. But beyond that guess, I'm clueless.