Myrtaceae
Variation in Myrtaceae flowers and fruits. Photos: E. Lucas, G. Bramley, F. Forest.
The Myrtaceae (Eucalyptus, clove or guava family) is an ecologically important family of c. 140 genera and between 3,800 and 5,600 species. Centres of diversity for the family are in the wet tropics, notably South America, Australia and Tropical Asia. Little baseline knowledge exists for the family and that which is available is 150 years out of date for most tropical areas (except Australia). While resolution of the taxonomy of the family at tribal level is progressing, the need for further work within the largest tribe – the fleshy fruited and primarily Neotropical tribe Myrteae, is great. Due to high morphological variation at all taxonomic levels, Myrtaceae has a reputation in the Neotropics as being a ‘difficult’ family to identify even to genus. Taxonomic data is lacking on every front, the lack of taxonomic revisions matched by the lack of correctly named and curated collections in the world’s herbaria. The subtribal classification of Myrteae is unstable, as are generic boundaries within it, and the number of undescribed species is high because their description is often frustrated by the difficulty in confidently assigning a specimen to genus.
Neotropical Myrtaceae are particularly species rich in some of South America’s most threatened habitats. The two largest Neotropical genera are Eugenia and Myrcia comprising approximately >550 and 250-500 species respectively with species diversity reaching its peak in the Brazilian Atlantic rainforest and cerrado, habitats that are disappearing rapidly under human pressure. Only 4% of the Atlantic forest remains, with these fragments containing up to 90 species of Myrtaceae per ha., many of which are undescribed. Because of the importance of Myrtaceae and the degree of skill required to identify its species, a complete ecological description of the areas in which it is so diverse depends upon a taxonomic revision of the family. Such a revision must be undertaken as soon as possible as many of these habitats are disappearing at an unprecedented rate.
Myrtaceae is economically important in the spice, fruit, timber and pharmacology industries with other economic potential beginning to be realised (bioactive compounds, vitamin-rich soft fruits etc.). Eucalyptus is widely cultivated to provide shade and for the timber and pulp industries. Syzygium aromaticum (clove) and Pimenta dioica (allspice) are important in the spice industry. Pimenta racemosa (bay rum), Melaleuca (cajeput) and Eucalyptus provide oils for the perfume industry, while antiseptic oils are extracted from Eucalyptus, Melaleuca alternifolia (tea tree), Callistemon and Leptospermum. Almost all fleshy fruited Myrtaceae are edible; economically important fruits are Psidium guajava (guava) and Syzygium aqueum (rose apple), with many lesser known species locally important for juice, sweets and jams, such as Myrciaria cauliflora (jaboticaba) and Eugenia uniflora (pitanga).