Iridescent plants are different colors, depending on the viewing angle. While you may be unfamiliar with iridescence in plants, you’ve seen it in soap bubbles, peacock feathers, CDs, and butterfly wings. Iridescence results from diffraction or when two or more semi-transparent surfaces reflect light and produce an interference pattern. Both iridescent leaves and iridescent flowers exist in nature, but most of the flowers don’t display a vivid color shift because the underlying pigment masks the change. Here is a list of iridescent house plants (iridescent leaves) and iridescent flowers and a look at why plants produce color shifts.
Why Plants Have Iridescent Leaves
Only a few plant species have iridescent leaves and these tend to be tropical rainforest specimens that spend their lives in the shade beneath the tree canopy. Scientists examining leaves with an electron microscope found the plants use modified chloroplasts (iridophores) to extract as much light as possible from their dim environment. Specifically, the chloroplasts have specialized thylakoids in their chloroplasts. In most plants, these thylakoids appear randomly organized. In iridescent plants, the thylakoids are precisely arranged, more like a crystal. The structure reflects away blue light, producing a blue iridescence. In exchange, the thylakoids are 10% better at absorbing the red and green light that plants need to perform photosynthesis and make food. If the plant gets more light, it adapts and uses regular chloroplasts to make food. So, when you grow these plants in sunlight, they cease to be iridescent.
List of Iridescent House Plants
Here is a list of iridescent house plants. Some of these plants are quite rare, but peacock begonia and peacock fern are often available and Persian shield is a relatively common bedding plant. Peacock begonia and peacock fern require filtered light and high humidity, while Persian shield tolerates some sunlight.
- Coral bells (Heuchera sp.) – The iridescence depends on the species. Silver, red, and purple are example colors. Heuchera “Silver Gumdrop” is a noteworthy cultivar.
- Elaphoglossum wurdackii – Fern that displays blue iridescence. Not commonly available for sale, except from nurseries specializing in rare ferns.
- Mopania caudata – A shade-loving sedge with a blue iridescence.
- Peacock begonia (Begonia pavonina) – Dark bronze leaves that display blue iridescence when grown in low light, high humidity, and cool temperatures.
- Peacock fern or peacock spikemoss (Selaginella willdenovii, S. uncinata, and other species) – Delicate green fronds with electric blue to turquoise shimmer when viewed from certain angles. Sometimes displays pink iridescence. Requires filtered light and high humidity.
- Peperomia – Some species of this common houseplant are iridescent.
- Persian shield (Strobilanthes dyeranus) – Green leaves with purple and silver iridescence. Commonly available and suitable as an outdoor annual.
- Scarab fern (Microsorum thailandicum) – Striking blue iridescence, but only if grown in warm temperatures with indirect light.
- Stegolepis hitchcockii (and some other species) – Strap-shaped yellow-green to emerald green leaves that flash electric blue. This plant grows and displays iridescence in sunlight.
Iridescent Flowers
Flower color is a bit more complicated than leaf color. While iridescent leaves use iridophores, flowers shift color by combining the surface structure of petals with pigment molecules. A region of a petal with a flat surface might act as a mirror, while cone-shaped projections can diffuse light, and striations can act as a diffraction grating. Pigments and vacuoles beneath surfaces moderate the resulting color.
The color shifts displayed by most iridescent flowers often aren’t very noticeable to human eyes. You’ll never see a flower as brightly iridescent as a peacock feather or beetle. Arguably the most vibrant iridescent flower is the sea holly (Eryngium sp.) The sea holly has spiny leaves and umbrels of iridescent blue and silver flowers.
Here is a list of iridescent flowers that can be grow as houseplants or garden plants:
- Black bat flower (Tacca chantrieri) – black, whiskered flower with rainbow iridescence
- Blue sea holly (Eryngium sp.) – blue-violet iridescence
- Hydrangea – some species display blue-violet iridescence when grown in acidic soil (e.g., Hydrangea serrata “Blue Billow”)
- Peacock iris (Moorea aristata) – White petals with iridescent blue eye.
Why Some Flowers Are Iridescent
Flowers are colored to attract insects for pollination. Insects, such as bees, tend to seek flowers of a particular color that are known to produce a lot of nectar. Scientists wondered whether the color change caused by iridescence might, therefore, confuse pollinators. A study using bumblebees indicates bees do get confused by perfect iridescence from artificial diffraction gratings, but actually have no trouble at all identifying natural (imperfect) iridescent flowers. In fact, flowers may use iridescence as a sort of billboard, where the color shifts advertise tasty flowers and help them stand out from a sea of green.
Iridescent Fruit
Iridescence isn’t limited to leaves and flowers. For example, Pollia condensata yields berries so colorfully iridescent that plant is nicknamed the marble berry. The berries are mostly blue, but display a rainbow of colors depending on the viewing angle and ripeness. The berry surface is smooth and reflective, like a mirror. Special stacked cells beneath the surface cause Bragg reflection, making the berry appear rather pixelated.
Where to Buy Iridescent Plants
Your local garden store may sell some iridescent plants, but your best bet is to search online to find a nursery or seed supplier that ships to your country. Search under both the common name and scientific name. Sea holly seeds are readily available, as are hydrangea and Persian shield plants. For more exotic plants, I found the best selection from growers on Etsy. Use caution with eBay and Amazon. Not every seller is reputable, so check ratings and reviews before making a purchase.
Do you own an iridescent plant, know of one I’ve missed, or have a recommendation for a supplier? If so, please post your experience.
References
- Funk, V. A., et al. (2007). Checklist of the Plants of the Guiana Shield (Venezuela: Amazonas, Bolivar, Delta Amacuro; Guyana, Surinam, French Guiana). Contributions from the United States National Herbarium 55: 1–584.
- Glover, Beverley J.; Whitney, Heather M. (April 2010). “Structural colour and iridescence in plants: the poorly studied relations of pigment colour.” Annals of Botany. 105 (4): 505–511. doi:10.1093/aob/mcq007
- Graham, Rita M.; Lee, David W.; Norstog, Knut (1993). “Physical and Ultrastructural Basis of Blue Leaf Iridescence in Two Neotropical Ferns.” American Journal of Botany. 80 (2): 198–203. doi:10.2307/2445040
- Jacobs, Matthew; et al. (2016). “Photonic multilayer structure of Begonia chloroplasts enhances photosynthetic efficiency.” Nature Plants. 2, 16162. doi:10.1038/nplants.2016.162
- Whitney, Heather M.; et al. (2016). “Flower Iridescence Increases Object Detection in the Insect Visual System without Compromising Object Identity.” Curr Biol. 26(6): 802-808. doi:10.1016/j.cub.2016.01.026
- van der Kooi, Casper J., et al. (2014). “Iridescent flowers? Contribution of surface structures to optical signaling.” New Phytologist. 23(2): 667-673. doi:10.1111/nph.12808