Edge or boundary.
The edge of the leaf blade.
The perimeter, or edge, of a leaf structure.
The edge; in the case of the cap, the area away from the disc toward and including the edge.
The edge of a leaf or petal.
The edge of any flat organ such as a leaf or petal. Features of the leaf margin such as teeth are important in plant identification.
A border or boundary such as the edge of a structure, or of a pathological specimen removed from the body surgically.