STUDIES OF PACIFIC ISLAND PLANTS. XXVI. METROSIDEROS COLLINA (MYRTACEAE) AND ITS RELATIVES IN THE SOUTHERN PACIFIC

The genus Metrosideros (Myrtaceae) is an abundant and taxonomically confusing component of the vegetation throughout much of its range. In the southern Pacific, from the New Hebrides eastward to the Society and Tuamotu Islands, the genus is represented by one variable species, M. collina (J. R. & G. Forst.) A. Gray, in which three widespread varieties seem to merit recognition. An attempt is here made to clarify the nomenclature and inter-relationships of these varieties. Additionally, two local endemics are related to the M. collina group-M. gregoryi Christophersen in Samoa and M. ochr antha A. C. Sm. (sp. nov.) in Fiji. THROUGHOUT ITS RANGE the genus Metrosideros has puzzled taxonomists who have required names for its component taxa. In Hawaii in particular, the genus is a strikingly abundant element of the vegetation, and to many floristic students it seems complex beyond current solution. The reference of all but a few Hawaiian forms to M. polymorpha Gaud. (Hillebrand, 1888) or to M. collina subsp. polymorpha (Gaud.) Rock (Rock, 1917) is a frequently adopted course, but detailed reconsideration would seem imperative. Research now in progress on the Metrosideros collina complex is especially welcome; in an initial paper Dawson (1970) has clarified the terminology and probable limits of the complex. The high degree of vagility of M. collina (sens. lat.) has recently been discussed by Carlquist (1972), quoting research by Carolyn Corn. The small seeds of this complex readily become airborne and can survive both the low temperatures of high air currents and soaking in sea water. Constant interchange of '-Received for publication 22 September 1972. This paper is based on research partially supported by a grant from the National Science Foundation. Number XXV in this series was published in J. Arnold Arboretum 54 (1973). Dr. J. W. Dawson, of Victoria University of Wellington, has kindly read a draft of the present treatment and has made valuable suggestions; the conclusions here expressed as to taxonomy and nomenclature, however, are the sole responsibility of the author. The author is indebted to the administrators of the following herbaria for making available their collections, which are cited as follows: Arnold Arboretum of Harvard University (A); Bernice P. Bishop Museum (BISH); British Museum (Natural History) (Bm); Gray Herbarium of Harvard University (GH); Royal Botanic Gardens, Kew (K); Department of Botany, University of Massachusetts (MAss); New York Botanical Garden (NY); Departments of Agriculture and Forestry, Suva, Fiji (suvA); and U. S. National Herbarium (-Ls). populations among the Pacific archipelagoes, therefore, has seemed to circumvent the isolation that accounts for the archipelagic endemism so frequent in other Pacific taxa. In an effort to understand the Fijian components of Metrosideros preliminary to a proposed floristic treatment of Fijian spermatophytes, I have reviewed some of the available herbarium material from the archipelagoes between the New Hebrides on the west and the Society and Tuamotu Islands on the east. As clarification of the Fijian taxa is the present objective, neither Hawaiian nor Marquesan forms have been studied; the latter (Brown, 1935) seem to approach the Hawaiian elements in their complexity and must be left for other students. The nomenclatural complications in this complex seem to rival the biological complications. Competing names had been used by botanists of the late eighteenth century concerned with Polynesian plants, but Asa Gray (1854) correctly appreciated the nomenclatural priority of Leptospermum collinum J. R. & G. Forst. (1775) and first made the appropriate binominal combination in Metrosideros. Gray's concept of the species included three varieties, vars. villosa, glaberrima, and vitiensis, but he referred the Forsters' epithet to none of them. The division of the complex into a number of infraspecific taxa appears to have some biological validity, but of course modern nomenclatural practice demands that the epithet collina be used for one of them. The populations of Metrosideros occurring from Fiji to the Tuamotus seem to me to be referable to a single species, M. collina, with the exception of two local endemics, the Samoan M. gregoryi and the Fijian M. ochrantha, which are discussed in this treatment.