Myrtle Family (Myrtaceae)

In a broader taxonomic sense, the Myrtaceae is a dicot family in the class Rosidae, which also includes the rose and mallow families. The Myrtaceae falls into the order Mytrales, along with the families Lythraceae, Punicaceae (pomegranates), and Onagraceae (evening primroses).

An unusual and taxonomically useful trait found in the Myrtaceae involves the vascular system of the stem. In most dicotyledonous plants the food conducting cells of the vascular system, the sieve elements of the phloem, surround the water conducting cells, or xylem. In young stems there is usually another group of large cells that appear open in sections viewed under a light microscope. This group of cells is called the pith, inside the xylem. Unusually, some phloem occurs inside the pith in species of the Myrtaceae.

Species of the Myrtaceae are noted for leaf dimorphism: the leaves produced when the plants are young tend to be round and held closely to the branch, while leaves produced when the plants are mature are much longer and thinner. Whether juvenile or adult, the leaves of plants in the myrtle family are opposite. Whenever a leaf is found on one side of the stem, another leaf is found on the opposite side.

The term myrtle, a common name for some species in the genus Myrtus, is also used as a common name for numerous other plants. These are not to be confused with species from the Myrtaceae. The best known plant called a myrtle, which is not a member of the Myrtaceae, may be the popular garden plant, crepe myrtle, (Lagerstroemia indica), of the Lythraceae or loosestrife family.

The Myrtaceae is commonly subdivided into two subfamilies, the Leptospermoideae, which is distributed mostly in Asia and Africa, and the Myrtoideae, found in tropical America, Asia, Australia, and the Pacific. The myrtle family is best known from Australia. Many species in the genera Eucalyptus, Calliostemon, and Verticordia, among others, are found in Australia. However, many genera such as Psidium are present in the Americas, and Myrtus of the Mediterranean and Northern Africa. The genus Eucalyptus is probably the best known representative of the Myrtaceae.