Since ancient times, people have cultivated plants not just for simple utility as sources of food, medicine, fiber, dyes, and other materials, but also for their beauty and the pleasure it brings into our lives. In the course of selecting for plants that are ever more attractive in their growers’ eyes, people have promoted plants with bigger flowers, brighter colors, exaggerated patterns, and larger displays.

Although these changes arose naturally by genetic mutations, such oddities likely would not have persisted for long in the wild since the ability of the plants to survive and reproduce may be compromised. Fortunately for these mutants, humans and human-dominated environments have become an important part of the earth’s ecosystem, and organisms that are able to catch human fancy can increase in abundance and become successful through their human benefactors.

A prime example of a plant favored and propagated by humans can be seen on practically every block of Capitol Hill at this time of year: the rose.

Thousands of human-bred cultivars exist, and different ones are popular as garden shrubs, container plants, cut flowers, and sources of perfume. In addition to these human-created varieties, there are also roughly 100 species which can be found growing wild in forests, woodlands, and grasslands across Asia, Europe, North Africa, and North America. There are four species native to Washington state. Take a look at a wild rose and what you’ll notice are five big colorful petals. Sticking above them is a mass of pollen-producing stamens in a ring, and in the very center, a cluster of the female seed-producing pistils.

Many of the cultivated roses we see don’t look quite like this. They have many more petals, creating a fuller shape to the flower that many people prefer. This deviation from the wild form, with an increase in the number of petals, is known as a “double flower.” It is also commonly seen in cultivated carnations, peonies, and camellias, among other plants. The original form of all these flowers is much simpler, usually with only five petals.

What is the mechanism behind the production of double flowers? Each part of the flower is controlled by different genes, just like different parts of our body were determined by the action of different genes when we developed. Petals are controlled by one set of genes, stamens by another set, and so on. In double flowers, the genes producing petals expand the area where they are active, taking over some of the parts where stamen-producing genes are usually expressed. A portion of those parts that normally become stamens instead develop into additional petals, and you have a double rose.

Roses generously lend their elegance to the summer cityscape. Reflect for a moment, and we are reminded of the fine genetic controls behind each flower (and indeed all life) but also that aberrations and differences can be the source of great beauty.