The Bastard Hogberry is a tree native to Mexico, Central and South America and the West Indies. Its fruit start out green but ripen to a brilliant iridescent blue when they fall to the forest floor. It is likely that the plant has evolved this unusual colouration because it helps foraging animals see the fruit, which they eat and disperse.
Similar to Blue Oil Fern leaves, plywood-packed fibres of cellulose within the cell walls of the fruit’s skin reflect light. Cellulose is not usually iridescent: it is the same material used to make cotton T-shirts and paper. It is not yet known how plant lays down these cellulose fibres, which is why we are growing it here. When it eventually flowers and fruits, researchers will be able to analyse the ripening fruits to follow the development of the colouration.
Fabrics using cellulose fibres similar to those found in the Blue Oil Fern and Bastard Hogberry can change colour as they stretch. These fabrics could be used for tension sensors or cutting-edge camouflage.
The story of how we acquired the seeds of this plant is rather amusing. Professor Beverley Glover, the Director of the Botanic Garden, had seen one fruit and wished to study it further, but no other fruit were available. A colleague from the Department of Plant Sciences was undertaking an expedition to Central America, where the tree can be found, and Prof. Glover asked him if he might keep an eye out for any Margaritaria, with the hope that he could bring back some fruit to study.
The Plant Sciences researchers were staying on an island, and every morning had to take a small motor boat to the river bank to conduct their experiments. Despite their best efforts, they were unable to find any Margaritaria trees in the areas they were studying, and had given up hope of finding any. However, after one windy day, they returned to find that their boat was full of the fruit. Closer inspection revealed that the tree to which they had been tying their boat every morning was actually exactly what they had been looking for!