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Myrtaceae

The Myrtaceae (Eucalyptus, clove or guava family) is estimated to contain more than 5,500 species. It is the eighth largest family of flowering plants, of both economical and ecological importance.

A large number of Myrtaceae species are found in the wet tropics, particularly South America, Tropical Asia and Australia. Plants belonging to the family are often hard to identify and classify and it is estimated that a large number of species still remain undescribed. Baseline information on Myrtaceae taxonomy is becoming more readily available, in many cases with input from Kew. The need now, is to consolidate this data into usable taxonomic treatments with which to catalogue biodiversity.

Myrtaceae often occur in threatened habitats such as the Brazilian Atlantic rainforest or the wet forests of Indonesia, New Guinea and to a lesser extent, Africa.

Myrtaceae are economically important in the spice, fruit, timber and pharmacology industries: 

  • Eucalyptus is widely cultivated to provide shade and for the timber and pulp industries.
  • Clove (Syzygium aromaticum) and allspice (Pimenta dioica) are important in the spice industry.
  • Bay rum (Pimenta racemosa), cajeput (Melaleuca) and Eucalyptus provide oils for the perfume industry.
  • Antiseptic oils are extracted from Eucalyptus, tea tree (Melaleuca alternifolia), Callistemon and Leptospermum.
  • Almost all fleshy-fruited Myrtaceae are edible - economically important fruits are guava (Psidium guajava) and rose apple (Syzygium aqueum), with many lesser known species locally important for juice, sweets and jams, such as jaboticaba (Myrciaria cauliflora) and pitanga (Eugenia uniflora)

In addition to the economic use of the family, its ubiquity in threatened biomes suggests an ecological importance. This has been demonstrated in the Brazilian Atlantic forests where it has been shown to be a reliable indicator of patterns of total species richness within the biome.

Myrtaceae is furter remarkable in containing four large genera of over 500 species, an unusual occurrence that makes the family an interesting study group for those interested in the evolution of large taxa. Three of these are tropical and fleshy fruited, namely the two Neotropical genera, Eugenia and Myrcia s.l. and old world Syzygium. The fourth large genus is capsular-fruited Australasian Eucalyptus. Kew’s Myrtaceae research interest is focused primarily on the fleshy fruited tribes Myrteae and has strategically broadened in line with institutional priorities to include tribe Syzygieae in Africa.

Background

Work on Myrtaceae has been steady at Kew since the time of Bentham (generic overview), with a tropical Asian focus in the 1970s (A.J. Scott), a New World focus since the late 1980s, now expanded to include old and new world taxa with fleshy fruits (tribes Myrteae and Syzygieae). The current multi-disciplinary collaborative programme has been developed over the last 20 years, and has its foundations in:

  • Kew’s type-rich tropical collections
  • Strong cross-departmental links between the herbarium and the Micromorphology, Biological Interactions and Molecular Systematics sections in the Jodrell Laboratory
  • Nomenclatural expertise (essential in a family where the combined effects of biology and history have often resulted in nomenclatural disorder)

Kew staff have a broad generic view of the family, however, the overall focus of the team has been and continues to be, in resolving systematic relationships in the predominantly South American tribe Myrteae and promoting its conservation. At a lower taxonomic scale, the focus is on the large genus Myrcia s.l. (including Marlierea, Calyptranthes and Gomidesia), comprising c. 750 species and >1,000 binomials). The objectives are achieved by producing consistently high quality data within Kew and from collaboration with an established network of global Myrtaceae researchers.