Whorl in the context of "Concentric objects"

In mathematics, a spiral is a curve which emanates from a point, moving further away as it revolves around the point. It is a subtype of whorled patterns, a broad group that also includes concentric objects.

In botany, a whorl or verticil is a whorled arrangement of leaves, sepals, petals, stamens, or carpels that 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 of opposite leaves is not called a whorl.

For leaves to grow in whorls is fairly rare except in plant species with very short internodes. Genera with species having whorled leaves include Galium, Nerium, Elodea, and Lilium. Leaf-like bracts may also be whorled (as in Trillium, e.g.). Leaf whorls occur in some trees such as Brabejum stellatifolium and other species in the family Proteaceae (e.g., in the genus Banksia). In plants such as these, crowded internodes within the leaf whorls alternate with long internodes between the whorls.