The Blue Chameleon Fruit: no pigment in Fruit, no pigment in Chameleon

Abstract

Structural colouration, rather than pigment, is a rare phenomenon in biology. This article compares the metallic blue fruit of Elaeocarpus angustifolius (blue quandong) with the non‑pigmentary blue of chameleons (Chamaeleonidae). Both achieve their colour through nanoscale arrangements that manipulate light, yet they belong to evolutionary lineages separated by tens of millions of years. The comparison highlights convergent evolution in optical signalling and concludes with a humorous but precise designation of the blue quandong as a "chameleon plant."

The Blue Quandong

The blue quandong (Elaeocarpus angustifolius), native to Northern Australia and Southeast Asia, is the only known fruit that appears truly blue without pigment (Vignolini et al., 2012). Its skin contains ultra‑thin cellulose layers arranged in nanoscale stacks, which selectively reflect blue wavelengths of light (Jacobs et al., 2013). When pigment extraction was attempted, the sample turned grey, confirming the absence of chemical colouration (Vignolini et al., 2012).

Ecologically, the metallic blue sheen enhances visibility in shaded rainforest environments, aiding avian seed dispersal (Thomas et al., 2010). Angiosperms, the broader lineage of flowering plants, originated approximately 140 million years ago (Magallón et al., 2015), while the Elaeocarpaceae family is estimated to have diversified between 65–100 million years ago (Coode, 1984).

Chameleons and Structural Blue

Chameleons (Chamaeleonidae) are renowned for their dynamic colour changes. Their blue hues are not pigmentary but arise from refraction of light on guanine nanocrystals within dermal iridophores (Teyssier et al., 2015). The spacing of these crystals determines the reflected wavelength, producing vivid blues and, when combined with yellow pigments, greens.

Fossil evidence places the origin of chameleons in the Paleocene–Eocene, approximately 60–100 million years ago (Raxworthy et al., 2002). Their colouration serves multiple functions: camouflage, thermoregulation, and social signalling (Stuart‑Fox & Moussalli, 2008).

Comparative Analysis

Conclusion

Both the blue quandong and chameleons achieve their striking blue through nanoscale manipulation of light, not pigments. Yet the plant lineage predates the reptile lineage by tens of millions of years. In a playful but scientifically grounded conclusion, we may declare:

The blue quandong is the true "chameleon plant" — the reptile merely copied the botanical trick, arriving late to the evolutionary masquerade.

References

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Jacobs, M., Vignolini, S., Wightman, R., et al. (2013). Structural colouration of fruits in Elaeocarpaceae. Proceedings of the Royal Society B, 280(1764), 20122788.

Magallón, S., Gómez‑Acevedo, S., Sánchez‑Reyes, L. L., & Hernández‑Hernández, T. (2015). A metacalibrated time‑tree documents the early rise of flowering plant phylogenetic diversity. New Phytologist, 207(2), 437–453.

Raxworthy, C. J., et al. (2002). Chameleon fossils and biogeography. Journal of Vertebrate Paleontology, 22(3), 770–776.

Stuart‑Fox, D., & Moussalli, A. (2008). Camouflage, communication and thermoregulation: The role of colour change in chameleons. Biological Reviews, 83(4), 547–569.

Teyssier, J., Saenko, S. V., van der Marel, D., & Milinkovitch, M. C. (2015). Photonic crystals cause active colour change in chameleons. Nature Communications, 6, 6368.

Thomas, D. B., et al. (2010). Structural colour in plants: Ecological and evolutionary perspectives. Annals of Botany, 105(4), 505–511.

Vignolini, S., Thomas, D. B., Kolle, M., et al. (2012). Structural colour in fruits. PNAS, 109(39), 15712–15715.