Can you believe the evolution of that?.....
"Well, lets see, I'm gonna need to be a funnel shape, but vertical so I can catch rain water and create a trap for things I need nutrients from. And I'm going to need to be stout, with a strong lip to hold things upright and together." And, lets see....my leaves need to be out of the way, so I'll make a petiole that directs the funnel away from the leaves and yet is strong enough to not get crushed by the weight. Hmmm, I"m gonna need to hold about 1.5 litres of water cause the rats around here are pretty big. And...I'll design myself a lip to try and attract things to eat".