Peacock begonia (Begonia pavonina): why its leaves are blue, and how to grow it

Daniel Platteau

A blue leaf… without blue pigment

A reader asked us on Facebook how to grow the peacock begonia. Good question, because it is one of the most astonishing plants you can grow at home. Seen from a certain angle, in soft light, its dark green leaf takes on electric blue reflections, like a peacock feather. Change the angle or put it in full sun, and the blue fades away.

This blue is not a colour in the usual sense: it does not come from any pigment. It is an effect of light reflected by a microscopic structure, as on a soap bubble or the wing of a morpho butterfly. And this structure sits where nobody expected it: in the chloroplasts, the tiny factories of photosynthesis.

Plant profile

The British botanist Henry Ridley described it in 1909, from plants collected in 1888 by Leonard Wray in the Telôm valley, along streams at altitude. Gardens by the Bay in Singapore, which displays it in its mountain conservatory, describes it as a plant of the humid, cool and shady understorey of the montane forests of Peninsular Malaysia.

The secret of the blue: chloroplasts as a “photonic crystal”

A 1996 discovery

In 1996, the botanists Kevin Gould and David Lee examined under the microscope the blue leaves of several Malaysian understorey plants, including the peacock begonia. In the upper layer of the leaf they found plastids (relatives of chloroplasts) with membranes stacked in very regular layers. Each layer reflects a little light, and the reflections add up to a single colour: blue. This is called interference, the same principle as the sheen on an oil puddle.

2016: these plastids help capture light better

Twenty years later, a team from the University of Bristol showed that these plastids, named iridoplasts, work like a photonic crystal. The layers that reflect blue are the very membranes where photosynthesis takes place. Their spacing slows down and traps green light, the light that dominates under the tree canopy after the leaves above have absorbed the red and the blue.

The result measured by the researchers: 5 to 10% more photosynthesis in low light. In a tropical understorey, where only a tiny fraction of the light reaches the ground, this small bonus matters. The researchers observed that the leaves only developed their blue sheen when they grew in near darkness, and that it slowly faded under strong light. The viewing angle matters too: seen head-on, the leaf can look simply dark green.

Other blue shade plants

The peacock begonia is not alone. Phyllagathis rotundifolia, a Malaysian member of the Melastomataceae studied alongside it in 1996, uses the same type of plastids. Some spikemosses (Selaginella willdenowii, S. uncinata) are also blue, but by a different means: a thin layer in their cell walls.

Growing it at home

A word of warning straight away: this is a collector's plant, rarely sold, that needs a controlled environment. The advice below is based on its native habitat and on the experience of hobbyists: no scientific growing guide exists for this species.

What it needs

Mistakes that make it decline

• Dry air: the leaf edges turn brown and dry out. This is the main cause of failure outside a terrarium.
• Too much light: the leaves lose their sheen and may turn pale or scorch.
• Excess water in a poorly ventilated terrarium: the rhizome rots. Open the terrarium for a few minutes from time to time.

Propagating it

It is propagated by rhizome division or by leaf cuttings with their petiole, laid on a moist substrate in a closed atmosphere. Malaysian researchers also propagate it in vitro, in the laboratory, for conservation: more than half of the 54 begonias native to Peninsular Malaysia are considered threatened.

Test yourself

Sources

Ab Aziz, R., Kandasamy, K. I., Zaman, F. Q., & Namasivayam, P. (2021). In vitro shoot proliferation of Begonia pavonina: A comparison of semisolid, liquid, and temporary immersion medium system. Journal of Academia, 9(1), 39–48. https://journal.uitm.edu.my/index.php/JOA/article/download/5181/2744/18960

ASPCA. (n.d.). Begonia. https://www.aspca.org/pet-care/aspca-poison-control/toxic-and-non-toxic-plants/begonia

Chareyron, D., & Combemorel, P. (2017, May 16). Les iridoplastes, ces chloroplastes iridescents. Planet-Vie (ENS). https://planet-vie.ens.fr/node/1495

Collection de Bégonias. (2016, May 15). Begonia pavonina. https://collectiondebegonias.wordpress.com/2016/05/15/begonia-pavonina/

Gardens by the Bay. (n.d.). Peacock begonia (Begonia pavonina). https://www.gardensbythebay.com.sg/en/learn-with-us/explore-resources/whats-blooming/begonia-pavonina.html

Gould, K. S., & Lee, D. W. (1996). Physical and ultrastructural basis of blue leaf iridescence in four Malaysian understory plants. American Journal of Botany, 83(1), 45–50. https://digitalcommons.fiu.edu/cas_bio/5

Hébant, C., & Lee, D. W. (1984). Ultrastructural basis and developmental control of blue iridescence in Selaginella leaves. American Journal of Botany, 71(2), 216–219. https://doi.org/10.2307/2443748

Jacobs, M., Lopez-Garcia, M., Phrathep, O.-P., Lawson, T., Oulton, R., & Whitney, H. M. (2016). Photonic multilayer structure of Begonia chloroplasts enhances photosynthetic efficiency. Nature Plants, 2, 16162. https://doi.org/10.1038/nplants.2016.162

Pao, S.-H., Tsai, P.-Y., Peng, C.-I., Chen, P.-J., Tsai, C.-C., Yang, E.-C., Shih, M.-C., Chen, J., Yang, J.-Y., Chesson, P., & Sheue, C.-R. (2018). Lamelloplasts and minichloroplasts in Begoniaceae: Iridescence and photosynthetic functioning. Journal of Plant Research, 131(4), 655–670. https://doi.org/10.1007/s10265-018-1020-2

POWO. (n.d.). Begonia pavonina Ridl. Plants of the World Online, Royal Botanic Gardens, Kew. https://powo.science.kew.org/taxon/105382-1

ScienceDaily. (2016, October 24). [University of Bristol press release on begonia iridoplasts]. https://www.sciencedaily.com/releases/2016/10/161024133913.htm