Flower shape in orchids is determined by two competing groups of proteins, reports a study published online this week in Nature Plants. This finding greatly extends our understanding of the mechanisms leading to the diverse beauty of orchid flowers.

Apart from normal petals, most orchid flowers have a large and irregular modified petal, called the lip. Lips attract insect pollinators and serve as a landing platform, which is thought to have given orchids a great evolutionary advantage by promoting reproduction.

Chang-Hsien Yang and colleagues examine the expression of a class of genes known to be associated with petal development. In their mature orchid flowers the expression pattern suggests that two protein complexes, the ‘L’ complex and the ‘SP’ complex, compete to promote the formation of the lip and standard petals, respectively. They call this mechanism the Perianth code, referring to petals and sepals.

The authors found that orchid species from many subfamilies with different types of lips and petals all obey this Perianth code. They were also able to convert lips into petals in two orchid species by reducing the activity of the L complex using gene silencing.

In an accompanying News & Views, Barbara Gravendeel writes that the discovery of the protein complexes provides “an important step towards fully understanding how orchids continue to lure pollinators despite the lack of [a material benefit].”