Science Fair Project Encyclopedia
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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. The plants are mostly woody, with essential oils, and most flower parts in multiples of five. The most distinctive feature of the family is that phloem is found in the pith inside the xylem as well as outside of it, not just outside as in all other plants. The leaves are evergreen, alternate (rarely 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, and in others, reduced to four in number. The stamens are usually very conspicuous, brightly coloured and very numerous.
The family Myrtaceae has approximately 3000 species in 130 genera. They have a wide distribution in warm-climate regions of the world, with the greatest concentration of species in Australasia and the Neotropics. Eucalyptus is the predominant tree genus in most of Australia, and the Mountain-ash (Eucalyptus regnans) is the tallest flowering plant in the world. Other important Australian genera are Callistemon (bottlebrushes) and Melaleuca (paperbarks). The genus Osbornia , native to Australasia, are mangroves.
The genera Heteropyxis and Psiloxylon, which some authorities include in Myrtaceae, are here placed as separate families, based on evidence of their divergence before the origin of the common ancestor of the Myrtaceae.
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