ORIGIN AND DISTRIBUTION OF ADmAmm~GPLANTS IN HAWAICI Lyndon Wester ABSTRACT Hawai'i has more than 800 known species of alien plants that are reproducing without direct human assistance. During this century, new plant species have been arriving at the rate of about five per year. Patterns of plant collecting in time and space suggest that other species await discovery and that data on the ranges of known species are far from satisfactory. The New and Old World tropics have supplied most of the adventive alien plants in Hawai'i, although other places, particularly those with which Hawai'i has close economic and cultural ties, have contributed significant numbers in recent years. INTRODUCTION The nature and derivation of native floras have long attracted the attention of biologists, but the rearrangement and wholesale homogenization of the world's biota caused by humans in the last 10,000 years has aroused comparatively little interest until recently. Contributing reasons for this are that alien plant invasions are generally short-lived, and that populations depend upon continued disturbance, are unstable, and are determined to a large extent on chance dispersal. Furthermore, there is a built-in preference for what is natural and rare and a prejudice against the commonplace and alien among biologists, except perhaps where economic factors are involved. To protect natural ecosystems, agriculture, and even urban areas from undesirable invasion from alien plants, reliable data about the alien species resent are needed. Information about how plants were introduced is help& 1 to plan means to limit further additions to the alien flora. Understanding generalized patterns of establishment and spread is also useful in managing problems that already exist. Wester \ Origin and Distribution ofAIien Plants DEFINITIONS AND DATA SOURCES Considerable confusion exists about terminology applied to introduced plants and weeds (Frenkel 1984; Smith 1985), so it is important from the outset to define, in exact terms, the subject of this study. The focus of the work here will be plants introduced to Hawai'i that have shown the ability to reproduce themselves, either sexually or ve etatively, and to spread without direct human assistance. Excluded, tt erefore, are the introduced plants cultivated as crops or ornamentals, although it must be recognized that new recruits for the naturalized alien flora often come from the plants cultivated intentionally by humans. Weeds may be categorized accordin to the degree of human disturbance they require for survival (Harlan ancf de Wet 1965; Hart 1976). Slight disturbance, such as a small opening in the canopy of a forest, may be sufficient to ensure the establishment of some species. However, ruderals, the plants of waste places, or the weeds of crops depend upon continual disturbance. Some species ma depend for their survival on humans to supply water, to act as local crispersal agents, to set or extinguish fires, or to eliminate competitors by mowing, trampling, or spraying. All alien plants that are reproducing and actively spreading, or that have done so in the past, were considered in this survey. The de ree of direct or indirect dependence on humans for the survival of the popuf ations was not taken into account. Excluded, however, were plants confined to cultivation or persisting without showing any tendency to s read after abandonment. Opinions as to whether species are disliked, we Pcomed as valued additions to the flora, or simply tolerated were not taken into consideration. There is no infallible way to determine whether a plant is indigenous or alien by its external characteristics. However, if a plant was not recorded in early botanical surveys, has no closely related indigenous relatives, seems incapable of dispersin over great stretches of open ocean without human assistance, and favors fisturbed habitats created by humans, it seems reasonably safe to assume the species is an alien. There is substantial agreement of opinion about the provenance of most species in Hawai'i; however, there is some disagreement about a small number of species that might be indigenous, Polynesian introductions, or very earl European introductions. Because many of these species h,ave spread we I'1 beyond cultivation, this question must be addressed in more detail. Exact and reliable information on the time and circumstances of an introduction is rarely available. Furthermore, many adventive aliens were first introduced as crop or ornamental species and only later did they escape from cultivation. It is rare for escapes to be recorded. In fact, a plant may spread for many years and build up a large population before it is noticed. For exam le, Oxyspora paniculata was observed growing as a planted species in a forest reserve in 1958 when a collector commented, "this plant does not spread, does not seem to be a pest" (B.P. Bishop Museum herbarium specimen 58128). Only in 1984 was a serious infestation found in the same area (Obata 1985). In the course of the present study, the earliest record of each alien species was sought, regardless of the situation where it was first found. Sources for this information included Wester \ Origin and Distribution ofAlien Plants 101 published floras, checklists, other written accounts, accession records of arboreta or botanical ardens, and botanical specimens. The ma'ority of first records (72%) are from herbarium specimens. The B.P. Bishop huseum herbarium was the most important source. However, other herbaria containing the collections of 19th century botanists were also searched for plants believed to be early introductions to Hawai'i. The collections consulted were U.S. National Herbarium, Gray Herbarium of Harvard University, British Museum of Natural History, Royal Botanical Gardens at Kew, Museum National d'Histoire Naturelle, Paris, Universitatis florentinae, Institute Botanico, Academy of Sciences of the U.S.S.R. in Leningrad, Harold L Lyon Arboretum at University of Hawaii, and Department of Botany, University of Hawaii. EARLY ALIEN INTRODUCTIONS Most of the main food and fiber crops used by the Hawaiians lack mechanisms of dispersal that would enable them to reach Hawai'i by natural processes. Handy and Handy (1972) believed that only 14 species were actually introduced by the Polynesians (Table I), whereas St. John (1973, 1978) and Nagata (1985) have a rather longer list of candidates. Included are weedy species, which may have been introduced accidentally, and strand trees of widespread distribution in the Indo-Pacific (Merrill 1946). The status of several other plants, conventionally considered aliens introduced by Europeans, must be reconsidered in the light of the rediscovery of collections made by the first botanists to visit Hawai'i. As there is considerable controversy surrounding these species, each will be discussed separately. 'Ahu'awa, (Mariscus javanicus) The first record of ahu'awa in Hawai'i comes from the collection by Lay and Collie, botanists on the Beechey voyage, in 1827 (Hooker and Arnott 1965). The plant is commonly found on sandy beaches, in taro (Colocasia esculenta) patches, and in marshes and may be one of the indigenous, pan- tropical wetland species whose seeds were widely dispersed by waterbirds; or rt could have been carried as an accidental passenger on taro corms. Kili'o'opu (K llinga nemoralis) Mam (186' 6) was apparently the first botanist to collect kili'o'opu, which was regarded as indi enous by Hillebrand (1965) and "long established" by St. John (19735 It was reported in Tahit~in 1769 by Banks and Solander (Merrill i954) and, l~keMoricw javanicw, may either be indigenous or one of those species spread accidentally by the Polynesians. Kiikae ua'a (Digitaria setigera) The !otanist David Nelson, who accompanied Cook to Hawai'i, was the first to collect botanical specimens of this plant in 1779 (St. John 1978). Since it is frequently found growing around pig pens and its Hawaiian name, kiikaepua'a, implies an association with pigs, it may have been carried alon accidentally when the Polynesians brought the pig to Hawai'i (Degener 19t? 2). Wester \ Origin and Distribution of Alien Plants Table 1. Plants associated with Hawaiian culture and land use. Handy & St. John St. John Nagata Handy 1972 1973 1978 1985 MAIN ECONOMIC PLANTS Aleurites moluccana * Alocasia macrorrhiza * Adocarpus altilis * Broussonetia papyrifera * Cocos nucifera ? Colocasia esculenta * Cordyline fnrticosa * Curcuma longa * Dioscorea alata * Dioscorea bulbifera * Dioscorea pentaphylla * Ipomoea batatas * Lagenaria siceraria * Musa spp. Nusthum sannentosum * Piper methysticum * Saccharum oficinarum * Schiwstachyum glaucifolium * S'%mmalaccense * Tacca leontopetaloides * Tephrosiapurpurea * Zingiber zerumbet * STRAND TREES AND SHRUBS Calophyllum inophyllum Cordia subcordata Morinda citifolia Thespesia populnea ACCIDENTAL INTRODUCTIONS Digitananasetigera Indigofera suf@ticosa Ludwigia octovalvis Merremia aegyptia Oxulis comiculata Urena lobata Waltheria indica OTHER POSSIBLE POLYNESIAN INTRODUCTIONS Kyllinga nemoralis Lycopersicon pimpinellifolium Lythrum maritimum Mariscus javanicus Solanum americanum Wgna adenantha Wester \ Origin and Distibution ofAlien Plants 103 'Inik6 (Indi o era su.ticosa) Hillebranf(f965) noted that 'inik6 was one of the most common weeds in the Islands but believed that it had been introduced in 1836 for the production of indigo. Nelson, the botanist with Cook, listed "Indigo era, Indigo" in a report, which Bea lehole's informant assumed was &&ofera