I had planted quite a few lettuces - and they grew really well - and I think I'm the only one who eats salads relatively regularly. Hence I could not keep up with the lettuce growth. I did keep cutting the leaves from the bottom, but they kept growing taller and taller until eventually they flowered. At this point I've cut them right back and have given the little ladies some nice treats.
So, this first photo is the flower that eventually forms on the top of a lettuce when it is left to grow to its full capacity.