Double-flowered

[4] Double flowers are the earliest documented form of floral abnormality, first recognized more than two thousand years ago.

A double-flowered variety of Marsh Marigold was discovered and cultivated in Austria in the late 16th century, becoming a valued garden plant.

[6] The first documented double-flowered mutant of Arabidopsis, a model organism for plant development and genetics, was recorded in 1873.

[7] The mutated gene likely responsible for the phenotype, AGAMOUS, was cloned and characterized in 1990 in Elliot Meyerowitz's lab as part of his study of molecular mechanisms of pattern formation in flowers.

When both copies of the gene are deleted or otherwise damaged, developing flowers lack the signals to form stamen and carpel segments.