Life in Technicolor
Indian paintbrush (Castilleja indivisa). PHOTO Wildflower Center
THE YELLOW OF SUNFLOWERS, the red of paintbrushes, the unmistakable blue of bluebonnets — behind every flower, there’s a story of how their color has evolved. Evolution has led 90 percent of all flowering species to rely on pollination by animals like birds and butterflies, and their flowers have perfectly adapted over a hundred million years to attract these critical helpers. You’ll find signs of pollinator-friendly adaptations in many flower traits: Some have landing pads for bees, while others hide their nectar deep within, rewarding only long-tongued moths. Some smell sweet to lure in butterflies, while others smell downright rotten, enticing flies to do the job. But it’s the colors of the rainbow that most often capture the attention of pollinators and we humans passing by a spring meadow.
FROM TOP Red buckeye (Aesculus pavia); trumpet vine (Campsis radicans); coral honeysuckle (Lonicera sempervirens). PHOTOS Wildflower Center
One of the most well-known evolutionary partnerships is between hummingbirds and red flowers. The birds’ long bills are perfectly suited for sipping nectar from tubular flowers like Indian paintbrush (Castilleja indivisa), red buckeye (Aesculus pavia), trumpet vine (Campsis radicans), cardinal flower (Lobelia cardinalis), and coral honeysuckle (Lonicera sempervirens). There’s a reason your hummingbird feeder is red like these flowers: Researchers have found that hummingbirds’ eyes are structured to accentuate reds, oranges, and yellows while muting blues. Red isn’t just their favorite color — it’s what stands out the most in their vision.
Meanwhile, blue flowers, like bluebonnets, owe their rare hue to pigment compounds that are modified by the plant’s cellular pH. It requires extra effort, but it’s worth it: Blue is a bee magnet. “Blue is one of the hardest colors for plants to produce,” says Dr. Sean Griffin, Director of Science and Conservation at the Lady Bird Johnson Wildflower Center. “It’s a great example of how evolution fine-tunes traits to attract specific pollinators.”
Other flowers attract attention by reflecting light. Active at night, moths and even bats are drawn to large, white flowers that shine in the moonlight. The poster child for nighttime blooms is the moonflower (Ipomoea alba), with its sweet scent and big milky blooms. The rain lilies (Cooperia pedunculata) that pop up after a springtime rain also open overnight, glowing bright to draw in nocturnal pollinators.
Many flowers even have colors outside of the spectrum of human vision. Birds and insects see the world differently than we do because their eyes detect wavelengths of light that ours can’t. Bees, for instance, can’t see red: Their eyes have receptors for the blues and greens we see, and for ultraviolet (UV) colors we can’t. Many flowers have UV patterns on their petals, invisible to humans, that guide pollinators like lights on a runway.
Biology doesn’t just tell us why these colors evolved, but also how. Pigments, chemical compounds in a plant’s petals, give each flower its characteristic hue. Carotenoids, for example, give flowers yellow color, while anthocyanins are responsible for many pinks and reds. You may have heard of these compounds before: Beta-carotene, the most famous carotenoid, gives carrots their orange color and sunflower petals their yellow. Anthocyanins, antioxidants famous for being in red wine and dark chocolate, are found in the petals of red natives like heartleaf hibiscus (Hibiscus martianus).
Even the absence of color tells a story. Some plants, like ghost pipe (Monotropa uniflora), are colorless, living their pale lives parasitizing fungi instead of photosynthesizing. It’s because they lack chlorophyll — the compound that allows plants to absorb energy from the sun — that ghost pipes don’t have the green typical of other plants.
The vibrant hues of flowers are more than just a pretty face — they reflect a hidden partnership between plants and their pollinators, forged over millennia. So, the next time you pause to admire a bright bloom, remember the extraordinary forces that led to the beauty before you. The diversity of colors we see in our native wildflowers is a reminder of the diversity of pollinators they rely on for survival, underscoring the importance of conserving both wildflowers and pollinators together, to ensure they persist — and we persist — for future generations.