Petal spurs, sacs, nectaries, and claws
Nectaries (glands that produce nectar) can be found on many plant parts. Many are found around the base of a pistil. Some are found on petals. These may be on relatively flat petals, or in spurs on petals.
A spur is a narrow, cone-like projection of a petal. There is generally a nectary at the end.
A sac is a more rounded pouch in a petal:
Some petals are clawed. Where an organ like a petal is narrow near the point of attachment and much broader distally (usually abruptly flaring out), the narrow proximal region is called the "claw" and the broader distal region is called the "limb". (Note that "limb" is also used to describe the distal, flared region of a corolla such as a salverform corolla.)
