Look closely at a lily pad sometime and you'll see that its shape is different from virtually any other leaf.
With most leaves, the stem attaches to one edge of the leaf. You can see how lily pads are different from other leaves if you imagine an insect crawling up the leaf.
On most leaves, the insect could climb directly from the stem onto the upper surface of the leaf.
Not so with a lily pad. The stem of the lily pad - which connects the flower to the bottom of the pond meets the leaf in the middle of its underside.
An insect crawling up the stem of a lily pad would have to climb over the underside of the leaf before climbing out onto the top.
In a pond, this leaf shape helps the leaf to float flat on the surface with the stem hanging straight down to the bottom.
Cecropia Tree's Leaf Shape
In the central American rain forests, the Cecropia tree benefits in a very different way from the same shape of leaf. In a rain forest, most trees are covered with vines that climb up the trunk.
When the vines finally grow out into the sunlight above the trees, they become stronger and heavier until they eventually kill the tree.
But just like our imaginary insect climbing up the stem, the vines can't get past the leaves of the cecropia tree. Since the vines can't reach the sunlight, they don't do well and the Cecropia trees are some of the only trees in the rain forest not loaded down with vines.
Lily pads and Cecropia trees grow in two very different environments, but a similar leaf shape helps them cope with two very different problems.