Whorl (botany)

Photograph and axial plane floral diagram ofFriesodielsia desmoides,showing thewhorledpattern of multipleconcentric objects.

Leaf whorls on aherbaceousLilium michiganense

Leaf whorls on a woody tree,Brabejum stellatifolium

In botany, awhorlorverticilis awhorledarrangement ofleaves,sepals,petals,stamens,orcarpelsthat radiate from a single point and surround or wrap around the stem or stalk.A leaf whorl consists of at least three elements; a pair ofopposite leavesis not called a whorl.

For leaves to grow in whorls is fairly rare except in plant species with very shortinternodesand some other genera (Galium,Nerium,Elodeaetc.). Leaf whorls occur in some trees such asBrabejum stellatifoliumand other species in the familyProteaceae(e.g., in the genusBanksia). In plants such as these, crowded internodes within the leaf whorls alternate with long internodes between the whorls.

Themorphologyof mostflowers(calledcyclic flowers) is based on four types of whorls:

1. Thecalyx:zero or more whorls of sepals at the base
2. Thecorolla:zero or more whorls of petals above the calyx
3. Theandroecium:zero or more whorls of stamens, each comprising a filament and an anther
4. Thegynoecium:zero or more whorls of carpels, each consisting of anovary,astyle,and astigma

A flower lacking any of these floral structures is said to beincompleteorimperfect.Not all flowers consist of whorls since the parts may instead be spirally arranged, as in the familyMagnoliaceae.

See also

• Cyclic flower
• Merosity
• Phyllotaxis