What kind of coat is always wet when you put it on?

Not from a sheep but a plant, I might help you sleep if you pant. My history is steep with respect that was scant.

I pose in the heat every hour. Naked except for a flower. It feels such a waste, to have fruit worth the taste, for my needles make most people cower.

Allegedly born from a Bell, A mixed truth they tell. I aged and learned new things, leaving behind my strings. I pass your secrets unbroken, and speech never spoken.

I'm green then I'm brown. I start high and then fall down. My flesh thick, my milk sweet, My shell like concrete. My name ends wrong, I've been a fruit all along.