A Revision of Xanthomyrtus (Myrtaceae)

Abstract

Xanthomyrtus was described by Diels (1922) with thirteen species in New Guinea, one in Sabah and one in New Caledonia. In addition Myrtus metrosideros Bailey, from northern Queensland, was suggested by Diels as possibly belonging to Xanthomyrtus. Diels distinguished Xanthomyrtus from Myrtus and related genera by the 4-merous flowers with thick triangular calyx lobes, the yellow, clawed petals, the few (I-2-)-seriate stamens and the 3-flowered dichasia with sessile flowers. Diels described eight new species of Xanthomyrtus, the remaining species were transferred by him from Eugenia or Myrtus; three of these were described by Ridley (1916) from West New Guinea, three described by Gibbs (1917) from the Arfak Mountains and one based on Myrtusflavida Stapf from Borneo. Diels (1924) later added one more species from New Guinea and cited further collections. However, in some of the species that he transferred to Xanthomyrtus the original collections had not been seen by him and were only known to him by the descriptions or by collections matched with descriptions. Many species were known only from a single or a few specimens and Diels (1922) cited only 24 collections. Merrill (1926) transferred Eugenia aurea Elmer and E. diplicosifolia C. B. Robinson, both from the Philippines, to Xanthomyrtus and later (1928) transferred two further Bornean species, Myrtus taxifolia Ridl. and M. moultonii Merr. Guillaumin (i939) recognized two species in New Caledonia, X. hienghenensis Guillaumin, with one variety, and X. sarasinii (Guillaumin) Guillaumin, including X. pergracilis Diels as a synonym of the latter. Merrill and Perry (1942) reviewed the species of Xanthomyrtus in New Guinea and described seven new species. Unfortunately many of the species previously recognized by Diels were known to them only through descriptions and specimens matched with the descriptions; several of the species described by them were incompletely known and they cite only 37 collections. Myrtus metrosideros, which tentatively was included in Xanthomyrtus by Diels (1922), is based on a leaf collection from northern Queensland. However, further collections matched with the type belong to Myrtus sect. Austromyrtus and no collections of Xanthomyrtus have been seen from Australia, although the genus may be expected to occur there. Xanthomyrtus pergracilis has been examined and is a species of Eugenia sens. str., and only a single species, X. hienghenensis, is recognized from New Caledonia; this species appears to be closely related to species in New Guinea.