In botany, a whorl is an arrangement of sepal

Sepal

A sepal is a part of the flower of angiosperms . Collectively the sepals form the calyx, which is the outermost whorl of parts that form a flower. Usually green, sepals have the typical function of protecting the petals when the flower is in bud...

s, petal

Petal

Petals are modified leaves that surround the reproductive parts of flowers. They often are brightly colored or unusually shaped to attract pollinators. Together, all of the petals of a flower are called a corolla. Petals are usually accompanied by another set of special leaves called sepals lying...

s, leaves

Phyllotaxis

In botany, phyllotaxis or phyllotaxy is the arrangement of leaves on a plant stem .- Pattern structure :...

, or branch

Branch

A branch or tree branch is a woody structural member connected to but not part of the central trunk of a tree...

es in which all the parts are attached at the same point and surround or wrap around the stem.There are four whorls in a general flower. They are calyx,corolla , androecium and gynecium.Calyx consists of sepals.Corolla consists of petals.Androecium consists of stamens(filaments and anther).Gynyecium consists of the female parts of a flower.They are stigma,style,ovary.A complete flower has all the whorls. If one or more floral structures are missing it is termed as an incomplete or imperfect flower.