   als, male parts, and female parts—and their typical sub-structures, they vary greatly between flowering plants. This variation encompasses all aspects of flowers, including size, shape, and colour. Flowers range in size from 0.1 mm (1⁄250 in) (duckweed) to 1 m (3.3 ft) in diameter (corpse flower). Additionally, the four main parts of a flower are generally defined by their positions and not by their function. Many flowers lack some parts, have parts that are modified for other functions, or contain parts that look like what is typically another part. In some flowers, organs such as stamens, stigmas, and sepals are modified to resemble petals. This is most common in cultivation (such as of roses), where flowers with many additional "petals" are found to be more attractive. Most flowers have symmetry. When the flower is bisected through the central axis from any point and symmetrical halves are produced, the flower is said to be regular (as in sedges). This is an example of radial symmetry. If there is only one plane of symmetry (as in orchids), the flower is said to be irregular. If, in very rare cases, they have no symmetry at all they are called asymmetric. Floral symmetry is a key driver of diversity in flower morphology, because it is one of the main features derived through flower-plant coevolution. Irregular flowers often coevolve with specific pollinators, while radially symmetric flowers tend to attract a wider range of pollinators.[note 3] In the majority of sp |