Climb for long enough in the Hengduan Mountains near Yulong, China, and you’ll probably spot Fritillaria delavayi. The small, charming plants have elegant green leaves and bell-shaped yellow flowers. Each one pops against the gray scree like a statement brooch.
Trek in the same mountain range just 65 miles away, and you’ll have to work much harder to see plants of the same species. There, F. delavayi plants are a dull tan, like the rocks they live on. Near Muli, they’re dark gray instead, and in Pujin, reddish-brown.
Why does this one species come in so many different colors? It might be hiding from you.
According to a paper published last month in Current Biology, F. delavayi has evolved several distinct color types because people harvest its bulbs. The finding suggests that the plant is the latest example in a growing list of species that humans appear to have inadvertently influenced into evolving new traits.
The impressive tricks animals use to disguise themselves are familiar to most people, but plant camouflage gets less attention. Yang Niu, a researcher at the Kunming Institute of Botany at the Chinese Academy of Sciences and lead author of the new paper, has spent years documenting possible examples of how plants conceal themselves. The mottled leaves of some forest plants may make it harder for herbivores to spot them. Lithops, also known as “living stone plants,” seem to be masquerading as pebbles.
These plants are generally trying to fool something in particular. Corydalis benecincta, another alpine plant Dr. Niu studies, has “a specialist enemy,” he said — a butterfly that nibbles its leaves. Possibly in response, the normally green plant has evolved a subtler gray morph.
“Other such kinds of camouflaged plants reported in other places all over the world — they also have enemies,” he said. The divergent coloration of F. delavayi was initially puzzling because no animals seemed to eat it.
But the bulbs of this and other Fritillaria plants are common medicinal ingredients, used to treat coughs. People have been harvesting them for over 2,000 years. What if this plant’s enemy is us? If so, F. delavayi plants in areas that experience more intense collection should be better camouflaged than those in places where people pick them less.
To test this, the researchers focused on eight plant populations. To judge the harvest pressure at each site, they asked for records from herb dealers and used those to figure out what proportion of each F. delavayi population had been picked annually for six years. They also estimated how difficult it was to collect the plants at different sites.
To determine how closely the plants matched their backgrounds, they took rock and leaf samples from each site, and compared the color and intensity of the light they reflected.
And to establish whether a closer match actually makes the plants more difficult to see, they created an online game called “Spot the Plant” — which shows players photographs of F. delavayi plants in different locations, with instructions to click on them as fast as they can. Local collectors also told the researchers that they had noticed plants in certain places were better camouflaged, Dr. Niu said.
When they put these metrics together, they matched up as expected. For F. delavayi populations that are largely left alone, it’s easy enough being green. But those under high harvest pressure now fade into the background, whether that’s tan, reddish-brown or gray.
The study makes “a fairly convincing case” that humans are driving the camouflage of this plant, said Ilik Saccheri, a professor of ecological genetics at the University of Liverpool who studies color change in moths and butterflies and was not involved in this work. However, he added, more experiments would bolster the evidence.
As people continue to manipulate other species, it’s good to remember that other species have moves to make in response.
“Humans have been artificially selecting all sorts of plants, animals and yeasts for thousands of years,” Dr. Saccheri said. “This is a nice example of unintentional selection.”