Plants come in a wide variety of colors, ranging from greens to reds, oranges, purples, blues, and more. The colors serve important functions for the plants related to photosynthesis, attracting pollinators, environmental adaptation, and protection. Understanding why plants have different pigments that result in varying colors can provide insight into plant biology, evolution, and ecology.
Photosynthesis and Chlorophyll
The most common color in plants is green. This is due to the presence of chlorophyll, the green pigment necessary for photosynthesis. Chlorophyll absorbs blue and red light from sunlight while reflecting green light, giving plants their verdant hue. The chemical structure of chlorophyll makes it an extremely efficient photosynthetic pigment, allowing plants to convert sunlight into energy and fuel plant growth. Nearly all plants contain chlorophyll, making green the predominant plant color.
Other Photosynthetic Pigments
While chlorophyll is the primary photosynthetic pigment, plants also contain various other pigments that aid in photosynthesis by absorbing different wavelengths of light. These accessory pigments include carotenoids, anthocyanins, betalains, and phycobilins.
Carotenoids are red, orange, and yellow pigments that absorb blue and green light. They are present in the leaves and fruits of many plants and also provide some photoprotection. Anthocyanins are water-soluble purple, red, and blue pigments located in cell vacuoles that may help leaves absorb light in shaded conditions. Betalains are red and yellow pigments substituted for anthocyanins in some plant families. Finally, phycobilins are red and blue pigments present in red algae and cyanobacteria that aid photosynthesis.
The combination of all these pigments allows plants to absorb light energy across the visible spectrum for use in photosynthesis. The particular mix of pigments present influences the final color of a plant.
Attracting Pollinators
Flowers utilize specific colors to attract pollinators and advertise the presence of nectar and pollen as a food source. Bees have color vision tuned to greens, blues, and ultraviolets. Butterflies can see reds, oranges, and yellows. Birds discern reds, oranges, blues, and greens. Flowers have evolved to produce colorful pigments that are visually salient to their pollinators.
For example, red flowers are prized by hummingbirds, while bees prefer purple and yellow flowers. The types of pigments present are optimized to appeal to pollinator color perception. This mutualistic relationship benefits both the pollinators that obtain food and the plants that are reproduced.
| Pollinator | Favorite Flower Colors |
|---|---|
| Bees | Purple, yellow |
| Butterflies | Red, orange, yellow |
| Birds | Red, orange, blue, green |
Environmental Adaptation
Plant colors can also evolve as adaptations to environmental conditions. In some cases, pigments act as sunscreens to protect leaves from damage by ultraviolet light or excessive solar radiation. The waxy bloom on some leaves and fruits filters intense sunlight. Red pigments in leaves attract blue and green light for photosynthesis while shaded from extreme red/orange light. Some alpine plants are hairy or red to absorb heat in cold climates.
Anthocyanins may defend cold-climate plants during autumn by blocking photo-oxidative damage as green chlorophyll breaks down. The particular combination of pigments can be optimized for the ambient light conditions and temperatures where plants grow. This tunes plant colors to local environments.
Defense and Signaling
Pigments serve numerous defensive and signaling functions in plants. Some plant colors camouflage or blend leaves against herbivores. Other colors signal toxicity or poor taste to deter herbivores and fungi. Redleafed plants invest heavily in anthocyanins as feeding deterrents. Some purple or black fruits use pigments to defend ripening fruits. Additional uses include sunscreen, free radical scavenging, and anti-fungal/anti-bacterial activity.
Pigments also facilitate plant-plant signaling. Growth of competitor neighbor plants causes some species to upregulate red pigments. Red coloration in leaves or stems may signal carpets of dense growth where red light prevails. In fall, red colors warn aphids to migrate off leaves before leaf drop. Thus, plant colors communicate and coordinate important ecological interactions.
Differences Between Plant Groups
The diversity of plant color is further expanded by structural differences in pigments between plant groups. Flowering plants primarily use anthocyanins to generate red, purple and blue colors. Non-flowering plants like ferns and mosses employ phlobaphenes instead. Red algae solely possess phycoerythrin resulting in characteristic red hues.
Within flowering plants, monocots like orchids use cyanidin pigments for reddish-purple flowers, while dicots like roses achieve similar colors from pelargonidin. These variations in pigment chemistry expand the color palette among different plants. Evolutionary divergences in pigment pathways lead to unique specialization in color.
Conclusion
In summary, plants exhibit a wide range of colors due to specialized pigments tailored to their functional roles. Chlorophyll enables photosynthesis across all plants. Additional pigments expand light absorption for photosynthesis. Colors attract mutualistic pollinators and deter pests. Adaptive purposes include heat absorption, light filtering, anti-oxidation, and anti-microbial defense. Structural differences in pigment biochemistry extend color diversity across plant groups. This multiplicity of functions is why plants have evolved so many distinctive colors. Understanding the reasons behind plant color variation provides insight into the biology, ecology and evolution of different species and environments.
