The term broadleaf weed usually pertains to weeds with broad or wide leaves and a pair of cotyledons, or seed leaves. Seed leaves or cotyledons are usually the first pair of leaves to appear as the plant emerges through the soil. Some broadleaf weeds have large square seed leaves. Other broadleaf weeds have seed leaves of another shape.
Seed leaves are normally thicker and more fleshy than leaves that develop later.
The size, shape and sometimes the odor of seed leaves can be used to distinguish some broadleaf weeds from one another. One key that aids in the identification of broadleaf weeds is the arrangement of the leaves. The arrangement of the leaves on a plant will vary for different species. Some broadleaf weeds have leaves arranged alternately on the stem, some have leaves arranged opposite each other, and some have leaves arranged in a whorl about the stem.