A revision of the south-western Australian species of Micromyrtus (Myrtaceae) with five antisepalous ribs on the hypanthium
Among the species currently included in Micromyrtus Benth., two main categories are distinguished here on the basis of hypanthium ribbing, one characterised by having antipetalous ribs and usually also antisepalous ones, the other by having antisepalous ribs but no antipetalous ones. Most species belong to the latter category, including the lectotype selected here for the genus, Micromyrtus drummondii Benth. nom. superfl. [= M. obovata (Turcz.) J.W. Green]. A key is given to the 14 Western Australian members of this group, and the eight south-western species, including five new species, are revised. Micromyrtus erichsenii Hemsl. is reinstated and the new species M. monotaxis Rye, M. ninghanensis Rye, M. papillosa J.W. Green ex Rye, M. rogeri J.W. Green ex Rye and M. uniovula Rye are illustrated. Three of these new species have an ovule number of one, lower than any previously recorded for the genus, and four of them have conservation priority.