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

round shape - a shape that is curved and without sharp angles

verticil - a whorl of leaves growing around a stem

line - a mark that is long relative to its width; "He drew a line on the chart"; "The substance produced characteristic lines on the spectroscope"