Accessory nail of the fifth toe

The accessory nail of the fifth toe, also known as petaloid toenail, is a physical trait of the small toe, where a minuscule "sixth toenail" is present in the outer corner of the nail situated on the smallest toe.

Description
The trait can be observed on either one or both feet, where there is a separation of the toenail situated on the smallest toe. The separated part of the nail forms a smaller "sixth toenail" on the corner of the larger, or "main" section of the toenail, on the outermost side of the foot, which protrudes outwards from the corner of the larger nail. The additional "nail" can be cut with a nail clipper, just like any other nail.

Causes
The cause is poorly understood due to a lack of research, but genome-wide scans indicate that it is a heritable trait, and could be autosomal dominant. However, the wide variance in the size and structure of the accessory nail indicates that the trait may not follow a Mendelian pattern of inheritance, and may instead be a complex trait affected by multiple genes with minor genetic effects.

Treatment
Most people do not seek out treatment, because the accessory nail typically does not cause pain or other symptoms that interfere with everyday activities. For those who do choose treatment, one option is surgical or chemical matricectomy--complete removal or destruction of the nail matrix--which has been used for successful removal of the accessory toenail.

Prevalence
Stereotypically endemic to Han Chinese, it is observed in people from all ethnicities and races.

Legend
Chinese mythology has it that during the time of the Yellow Emperor, there were two types of people living in China: those who were the descendants of the Yellow Emperor, and those who were nomadic Qiang people. The Henan people, led by Yin Wang, attacked the Qiang and abducted a Qiang woman, who later tried to escape. Yin Wang stabbed her in the abdomen as she tried to escape, so she gave birth to two children with a scar on the small toe of the foot. The children were taken back by Yin Wang for adoption, and their descendants were born with double nails on their small toes.