Oceania: Antidepressant Medicinal Plants

Abstract

Despite having the smallest land mass of the World Wildlife Fund (WWF)-declared ecozones, Oceania is amongst the most diverse floral regions of the world. Geographically, the region consists of Australia and New Guinea as the largest land masses, as well as the islands of Melanesia, Micronesia and Polynesia. Due to the island nature of the region, the flora has developed in isolation in various climatic conditions within the region, resulting in an extremely high degree of endemism. Furthermore, the harsh climatic conditions in some regions have resulted in a wealth of unique phytochemicals not found in plants from other regions globally. Coupled with possibly the world’s oldest continuous human inhabitation on the Australian mainland and a diversity of cultures in other Oceania regions, this has led to complex and sophisticated ethnopharmacological systems. Medicinal plants with unique properties have long been recognised by indigenous Oceania populations, and this lore has been passed from generation to generation. Whilst often not well recorded, there is a wealth of knowledge of the medicinal value of the regions’ floral species for all types of therapeutic purposes. This chapter focuses on the plants of the region with known antidepressant uses and/or those plants which have phytochemistry consistent with antidepressant properties. This is by no means an exhaustive list, but instead serves to highlight some of the best known examples (e.g. kava-kava) and discuss examples of plants with established antidepressant mechanisms. For example, whilst we discuss the calmative properties of the Australian plant Backhousia citriodora, many other aromatic plants with similar essential oil components and thus similar therapeutic properties exist in the region and are not discussed here for the sake of brevity. Furthermore, despite the high degree of endemism of Oceania flora, several well-known species (e.g. Areca catechu L. and Nelumbo nucifera Gaertn.) have wide geographic ranges. Indeed, whilst native to Oceania, A. catechu is better known as a component of the pharmacopoeias of other regions (e.g. India). However, these species also make an important contribution to Oceanic antidepressant medicinal plants and are therefore discussed in this chapter.