Myrtaceae

The Myrtaceae or Myrtle family are a family of dicotyledon plants, placed within the order Myrtales. Myrtle, clove, guava, feijoa, allspice, and eucalyptus belong here. All species are woody, with essential oils, and flower parts in multiples of four or five. One notable character of the family is that the phloem is located on both sides of the xylem, not just outside as in most other plants. The leaves are evergreen, alternate to mostly opposite, simple, and usually with an entire (not toothed) margin. The flowers have a base number of five petals, though in several genera the petals are minute or absent. The stamens are usually very conspicuous, brightly coloured and numerous.

The family Myrtaceae has at least 3000 species distributed in 130-150 genera. They have a wide distribution in tropical and warm-temperate regions of the world, and are typically common in many of the world's biodiversity hotspots. Genera with capsular fruits such as Eucalyptus, Corymbia, Angophora, Leptospermum, Melaleuca, Metrosideros are absent from the Americas, apart from the monotypic genus Tepualia in Chile. Genera with fleshy fruits have their greatest concentrations in eastern Australia and Malesia (the Australasia ecozone) and the Neotropics. Eucalyptus is a dominant, nearly ubiquitous genus in the more mesic parts of Australia and extends north sporadically to the Philippines. Eucalyptus regnans is the tallest flowering plant in the world. Other important Australian genera are Callistemon (bottlebrushes), Syzygium, and Melaleuca (paperbarks). The genus Osbornia, native to Australasia, are mangroves. Eugenia, Myrcia, and Calyptranthes are among the larger genera in the neotropics.

Historically, the Myrtaceae were divided into two subfamilies.
 * Subfamily Myrtoideae have fleshy fruits and opposite, entire leaves. Most genera in this subfamily have one of three easily recognized types of embryos. The genera of Myrtoideae can be very difficult to distinguish in the absence of mature fruits. The Myrtoideae are found worldwide in subtropical and tropical regions, with centres of diversity in the Neotropics, northeastern Australia, and Malesia.
 * Subfamily Leptospermoideae has dry, indehiscent fruits (capsules) and leaves arranged spirally or alternate. The Leptospermoideae are found mostly in Australasia, with a centre of diversity in Australia. Many genera in Western Australia have greatly reduced leaves and flowers typical of more xeric habitats.

The division of the Myrtaceae into the Leptospermoideae and Myrtoideae was challenged by a number of authors, including Johnson and Briggs (1984), who identified 14 tribes or clades within the Myrtaceae, and found the Myrtoideae to be polyphyletic. A molecular analysis by Wilson, O'Brien et al. (2001) found eleven strong groupings within the family, including many of the groupings identified by Johnson and Briggs. Further molecular analysis by Sytsma and Litt (2002) found that the Neotropic Myrtoideae grouping fit within the paraphyletic Leptopermoideae.

The genera Heteropyxis and Psiloxylon, which some authorities include in Myrtaceae, are here placed as separate families by most authors, based on evidence of their divergence before the origin of the common ancestor of the Myrtaceae.