Dendrobium sect. Ceratobium (Orchidaceae) in the Pacific Islands

Abstract

Summary. A key is provided for the identification of the 11 species of sect. Ceratobium found in the Pacific from the Solomon Islands eastwards. Three of these are newly described here. Some of the earliest species of Dendrobium sect. Ceratobium to be described were collected in the Pacific Islands and yet the confusion which surrounds their identification is considerable. A good account of the Orchidaceae exists for only one group of islands in the area, namely New Caledonia (Halle 1977). Groups such as the Solomon Islands and Vanuatu with possibly richer orchid floras are still comparatively unknown. In this account species of sect. Ceratobium from Bougainville and the Solomon Islands east to Samoa and south to New Caledonia are considered and a key is provided for their identification. This is the second paper in a series leading to a revision of the whole section, the first covering the Australian species (Lavarack & Cribb, in press). Plants of Dendrobium sect. Ceratobium such as D. tokai and D. gouldii from the Pacific Islands are frequently found in cultivation and several have been used to produce hybrids worthy of registration. However, they have never been easy to identify and names have frequently been misapplied. With the increased use of these species in hybridisation programmes in recent years it has become desirable to stabilise their nomenclature and to provide a key for their easier identification. The major problems for the taxonomist with these orchids are similar to those presented by New Guinea species summarised by Woods & Reeve (1980) being essentially those of location and interpretation of type specimens, assessing intraspecific variability and the recognition of the widespread range of some species. A further complication in sect. Ceratobium is provided by the probably not infrequent occurrence of natural hybridisation. This is difficult to identify from herbarium material and can only satisfactorily be proven by observations on living material.