round shape a shape that is curved and without sharp angles
corolla (botany) the whorl of petals of a flower that collectively form an inner floral envelope or layer of the perianth; "we cultivate the flower for its corolla"
calyx (botany) the whorl of sepals of a flower collectively forming the outer floral envelope or layer of the perianth enclosing and supporting the developing bud; usually green
structure,
construction a thing constructed; a complex entity constructed of many parts; "the structure consisted of a series of arches"; "she wore her hair in an amazing construction of whirls and ribbons"