Why Does This Flower Make Red Nectar?

Illustration for article titled Why Does This Flower Make Red Nectar?

Flowers usually expend their energy on making themselves bright and colorful. They bleach themselves white to stand out against dark leaves, or they deck themselves out in colorful patterns, but the overwhelming majority keep the nectar they offer clear. So, where did this flower’s red nectar come from?


For almost all flowers, the flower itself is the signal; the nectar is the reward. On Mauritius, though, there are certain flowers that change the pattern. Trochetia boutoniana shows off dark red nectar against a blue background and Trochetia blackburniana produces yellow nectar, which it shows off at the center of a yellow flower. Scientists on the island noticed the colored nectar right away, and searched for the cause. They found two causes—what one animal did, and what another animal didn’t do.

Right away, through casual observation, researchers found that a native bird species regularly visited the flower, sipping nectar and going from blossom to blossom. When they looked a little closer, they found that the bird was taking cruel advantage of the flower. While it sipped the nectar, it did so without taking on any pollen to brush on to the next flower. The bird was a nectar thief.

It took a little while longer to figure out which animal was willing to help the flower mate in exchange for a drink. Instead of birds being the primary pollinators of these plants, geckos carry the pollen from flower to flower. They prefer flowers with colored nectar. Just to be sure, a research team in 2006 tempted geckos with fake flowers that had either clear or colored nectar. The geckos preferred the red and yellow nectar every time.

It’s possible that the geckos expend more energy or take more of a risk to get from flower to flower than birds, and so require a definite signal that the flower they’re crawling to contains nectar. It’s also possible that the geckos, which are brightly colored with deeply contrasting flecks and stripes, might have an innate liking for bright colors and deep contrast. Whatever the reason, the flowers need a pollinator they can rely on and it seems they are catering to the only species that will make an honest deal with them.

[Source: The Royal Society Biology Letters]

Image: Klein Benjamin, Second Image: Biology Letters



You do not have to travel to Madagascar to see such. The invasive plant called purple loose-strife (Lythrum salicaria), which chokes wet ground in Minnesota, has a nectar that is faintly green in color. (It makes honey gathered by local bees the same color as motor oil.)