Cloves, guava, allspice and the world's tallest flowering plant are all myrtle relatives
The myrtle family ranges from spice-rack staples like clove and allspice to fruit such as guava and feijoa, and to Eucalyptus regnans, the tallest flowering plant on Earth. Every one of its roughly 5,950 species is woody and packed with essential oils, a lineage whose story was shaped by the breakup of Gondwana.
Myrtaceae belongs to the order Myrtales. Its members bear evergreen, simple leaves, usually smooth-edged and often opposite, and flower parts in fours or fives. Petals are sometimes tiny or missing, but the stamens are typically numerous, brightly coloured and eye-catching, as in the bottlebrushes. A 2016 estimate put the family at about 5,950 species in some 132 genera.
The family probably arose 60 to 56 million years ago in the Paleocene, and fossil pollen points to Gondwana. As the southern supercontinent split apart, isolated populations evolved separately, a process called vicariance that explains much of the family's diversity. Leptospermum on New Zealand and New Caledonia is a possible exception, since those islands may have been underwater when that group diverged.
Distribution follows fruit type. Genera with dry capsules, including Eucalyptus, Melaleuca and Leptospermum, are missing from the Americas except for Metrosideros in Chile and Argentina. Fleshy-fruited genera cluster in eastern Australia, Malesia and the American tropics, where Eugenia and Myrcia are large groups. Eucalyptus dominates the wetter parts of Australia and reaches north as far as the Philippines, and the Australasian genus Osbornia includes mangroves.
Classification has been reworked. Botanists long split the family into fleshy-fruited Myrtoideae and capsule-bearing Leptospermoideae. Johnson and Briggs challenged this in 1984, and by 2008 molecular studies had shown that fleshy fruits evolved twice from capsules, so the old split did not reflect ancestry. Many researchers now build on work by Wilson and colleagues from 2001. Two genera once given their own families, Heteropyxis and Psiloxylon, are now seen as the oldest surviving branches, and the latest scheme recognises 17 tribes in two subfamilies based on plastid DNA.
Source: Myrtaceae
