From what I gather, many of the species of Sarracenia evolved a lid to keep rain out of the pitchers. Rain would not only topple the pitchers over because of the weight making them less effective, it would also dilute the enzymes within the leaves and inhibit the uptake of nutrition. Yet here it is! Weird.
Interesting plant however, its extremely slow growing and not very willing to divide. I’ve had mine for three years now, and its still a single growth point. I think this is partially due to its decreased ability to capture prey, if my thoughts above are correct. I know that so far, mine is doing very well in the prey department. Its been very dry here this summer, and unlike most years, the pitchers are still standing. Normally by now they’ve been knocked to the ground because they’ve filled up with water.
So… I guess the question remains, why would this mutation happen? The only thing I can think of is that its a throw back to ancestor much like heliamphora that shows up from time time. As far as I’m aware there is a lidless form of leucophylla as well.