Lysimachia nummularia has thicker leaves, kind of like Bacopa. The leaves are somewhat oval, elongated to a point at the end.
Cardamon lyrata is wispier overall. The stems and leaves are very thin and delicate, often with slender roots growing at the leaf nodes. The leaves are more rounded, kind of like a spider web. They're also wavy.
You should know soon enough as it grows.
C. lyrata puts out very small leaves that reach to the light and enlarge as they get older. There's more space between leaf nodes.
L. nummularia grows more compact, and even though the new leaves are smaller, the space between the new leaves and old ones is uniform through the plant.
Here are examples of the different plants: first one is
Lysimachia nummularia and the second one is
Cardamon lyrata.
The above picture is from davesgarden.com.