Elaeocarpus angustifolius

Family / Families: Elaeocarpaceae
Scientific Name(s): Elaeocarpus angustifolius Blume
Institution(s): Fairchild Tropical Botanic Garden and Ho'omaluhia Botanical Garden
Location(s): Coral Gables, Florida, USA and Kāne'ohe, Oahu, Hawaii. USA
Entry Author(s): Tamara Bonnemaison
Copyright Holder(s): Susan Ford Collins aka jungle mama@Flickr and Drew Avery@Flickr
Image Permissions: Please contact the copyright holder for permission to use.
Photographer(s) Appreciation: Clearly I love seeds and fruits; I could not resist writing about the unusual blue fruit of Eleocarpus angustifolius when Susan Collins (aka jungle mama@Flickr) posted this stunning photo of the fallen fruit on a bed of leaves. I am also featuring a photo by Drew Avery@Flickr that illustrates the leaves and some of the growth habit of this tree species. Thanks Susan and Drew!
Tags: Elaeocarpaceae, Fairchild Tropical Botanic Garden, Ho'omaluhia Botanical Garden, Oxalidales, via Flickr

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Elaeocarpus angustifolius, or blue quandong, is a rainforest tree found in eastern Australia. It is quick to grow, reaching a height of 50 meters, and performs a key role in regenerating the rainforest after disturbance. In addition to the intriguing qualities shown in the photographs, this species also has beautiful fringed white flowers and stately buttressed roots.

The fruits of Elaeocarpus angustifolius, writes David W. Lee in a paper (PDF) published in Nature (Ultrastructural basis and function of iridescent blue colour of fruits in Elaeocarpus), achieve their colour in a very unusual way. While nearly all blue plant parts contain a pigment, the fruit of the nearly 60 species of the Elaeocarpus appear blue because their cuticles reflect blue light, in much the same way that peacocks (Pavo cristatus L.) and some beetles appear blue. Key to the iridescent blue qualities of Elaeocarpus fruit is the iridosome, a layer beneath the fruit’s outer cell wall that consists of parallel rows of translucent strands of just the right thickness and spacing to reflect only blue light. Lee posits that the evolutionary advantage of iridescent colour (as opposed to pigmented colour) are twofold: first, the brilliant blue colour is highly visible against a backdrop of green foliage, even persisting after the carbohydrate-rich mesocarp has been consumed. Second, most fruits are only able to photosynthesize when green, but by achieving colour through iridescence, the fruit of Elaeocarpus are able to continue to contribute to the plant’s carbon economy even when fully ripe.

Another, unrelated species that has iridescent blue berries is Pollia condensata. This article in Wired explains how the “natural world’s most intense colour” is produced. It seems the principles behind Pollia condensata‘s fruit colour are similar to the blue quandong.