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The plant

Xanthorrhoea is a genus of about 30 species of succulent flowering plants in the family Asphodelaceae. All of them are endemic to Australia. Grass trees grow in coastal heaths and in wet and dry forests of Australia. Fires burn the leaves and blacken the trunk, but the plant survives because the dead leaves around the stem serve as insulation against the heat of a wildfire. The dead trunk is a hollow ring of accumulated leaf bases. The name Xanthorrhoea means yellow flowing and refers to the yellow resin typical of the genus.

The resin

The resin is known as gum acaroides, Botany Bay resin and grass-tree resin. Two resins are produced by the genus, one yellow and one red. The yellow variety resembles gamboge in appearance and is reddish yellow outside and lighter yellow inside. The red variety resembles dragon's blood in appearance and is deep brown-red outside and bright red inside.

Chemistry

The yellow resin consists essentially of resin, cinnamic acid, a small quantity of benzoic acid and a trace of volatile oil. The free acid of the oil distilled from the yellow resin was identified as cinnamic acid. The oil from the red acaroid resin contained cinnamic acid, both free and as an ester, and also styrene. The resin is soluble in alcohols and alkalis but insoluble in water and hydrocarbons.

Uses

Resin collected from the plant was used in Australia until the mid-twentieth century. It was burnt as incense in churches and served as a base component of a varnish used on furniture and in dwellings. It was also used as a polish and coating on metal surfaces, including stoves and brass instruments. It served as well in industrial processes such as sizing paper and making soap and early gramophone records. The resin has been used chiefly as a substitute for shellac and for making coloured varnishes.

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