Cotyledons are the first pair of leaves to emerge. The shape of the cotyledon is a way to initially identify different broad leaf plants. Plants can have linear, oblong, oval, round or butterfly-shaped cotyledons and different extremes of each. The next step in the identification of broadleaves is to notice other features of the plant. A single taproot, tuber, or rhizome can help distinguish between two similar plants.
Grasses can sometimes be a little more difficult to identify.
The characteristics that make each different can be very hard to see with the naked eye. Nearly all of the characteristics for grasses are found in the collar region. This is the area of the blade that bends off of the stem. In this area, you need to look for ligules and whether they are absent, smooth, jagged, small or large. Whether or not the area is hairy and how long, and how much and where the hair is found are all important.