Question

how can you identify a dicot and a monocot plant looking at their leaves?

Answer 1

The difference is more than the leaves. Angiosperms (flowering plants) are a classification of plants. A cotyledon is a leaf embryo in a seed-bearing plant. So, by extension Monocotyledonae and dicotyledon vary by one or two embryonic leaves. You will notice this when the seeds germinate and poke through the soil. Green beans are a good example of a dicot as two leaves appear shortly after breaking through. Grasses are a good example of a monocot.

There are many other differences other than the typical parallel leaf veins found in monocots and netted leaf veins found in dicots. Here is a nice link with good pictures denoting some of the other differences in characteristics.

Answer 2

Leaf venation in monocot is parallel and in dicot is reticulate