Pacific Island Ecosystems at Risk (PIER)

Report on invasive plant species in American Samoa

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Dangerous species not known to be in American Samoa

Species that are invasive elsewhere and are likewise invasive or have the potential to become so in American Samoa

Species that are not known to be invasive elsewhere but have the potential to spread in American Samoa

Species that are mentioned or listed as weedy or invasive elsewhere and are common or weedy in American Samoa

Native and naturalized species exhibiting aggressive behavior

Strategies for dealing with invasive species


All islands


Manu‘a Islands




Appendix 1   References

Appendix 2   Species by category

Appendix 3   Invasive and potentially invasive species present on Tutuila

Appendix 4   Invasive and potentially invasive species present on Ofu

Appendix 5   Invasive and potentially invasive species present on Olosega

Appendix 6   Invasive and potentially invasive species present on Ta‘u


Observations on invasive plant species in American Samoa


James C Space and Tim Flynn


U.S.D.A. Forest Service

Pacific Southwest Research Station

Institute of Pacific Islands Forestry

Honolulu, Hawai‘i, USA


4 January 2000



4 January 2000

 Observations on invasive plant species in American Samoa

James C Space and Tim Flynn (1)

This is a continuation of the survey of islands in Micronesia and American Samoa for invasive plant species requested by the Pacific Islands Committee, Council of Western State Foresters. A survey of selected Micronesian islands was conducted in 1998 and was discussed in a previous report (2). This report is based on perceptions gained from a trip to American Samoa from 16 to 23 July 1999, including the islands of Tutuila, Ofu, Olosega and Ta‘u. The objectives were three-fold: (1) To identify plant species on the islands that are presently causing problems to natural and semi-natural ecosystems; (2) to identify species that, even though they are not presently a major problem, could spread more widely or spread to other islands where they are not present, potentially causing problems; and (3) to confirm the absence of species that are a problem elsewhere and, if introduced to American Samoa, could be a threat there.

During our visit local experts showed us sites of known infestations (3). We also had available copies of various botanical and weed surveys conducted in the past (see Appendix 1, References). A weeklong trip does not permit an exhaustive survey of the weed biota of the islands. However, the intent was to conduct an overall survey. Surveys of individual species or sensitive areas (such as the National Park of American Samoa) can and should be conducted as needed. This report summarizes our findings and makes some suggestions for further action.

For convenience and to be consistent with the Micronesia report, invasive species occurring in or of threat to the American Samoan islands have been grouped into five categories:

1.  Species that are invasive elsewhere in similar ecosystems but were not seen on our visit and are not reported in the literature as being present in American Samoa (174 species).
2.  Species that are invasive elsewhere and are also invasive or potentially invasive in American Samoa (20 species).
3.  Species that are not known to be particularly invasive elsewhere but have the potential to be invasive in American Samoa (5 species).
4.  Species that are invasive or weedy elsewhere and are common or weedy in American Samoa (80 species).
5.  Native species that exhibit aggressive behavior (7 species).

These species are listed in Appendix 2. In addition, species are listed by location within American Samoa in Appendix 3. Additional information about each species is located on a World Wide Web site, Copies of this web site are also available for installation on individual computers for rapid access.

There are numerous species that are invasive weeds in gardens, fields, and pastures and along roadsides but don’t seem to pose a particular threat to wildland ecosystems. These species are not included.

1. Dangerous species not known to be in American Samoa

While there are some serious or potentially serious weed species in American Samoa, some other major pests have not yet arrived. The worst of these include the following:

Cecropia obtusifolia and C. peltata, invasive tree species that are a problem in Hawai‘i and French Polynesia, respectively.

Chromolaena odorata (Siam weed), a highly invasive pan-tropical weed. It is present in a number of islands in the Marianas and Micronesia, as well as Papua New Guinea, the Philippines and Australia.

Coccinia grandis (ivy or scarlet gourd), a smothering vine that is showing potential for serious damage to the forests of Saipan. The vines climb over trees and form such dense cover that the forest underneath is completely shaded out and destroyed. It is also invasive in Guam and Hawai‘i and recorded in the literature as being present in Fiji, Tonga and Vanuatu. Whistler reports that it is present in Samoa, and this close proximity makes this species a special threat to American Samoa.

A rubber tree, Funtumia elastica (African rubber tree, pulu vao), has been reported by Whistler (1988) as being present and invasive in Samoa. As far as is known, this species is not yet in American Samoa, although another rubber tree (Castilla elastica, Panama rubber tree or pulu mamoe) is present (see below). F. elastica should be a priority species for exclusion or, if found, eradication.

Miconia calvescens (the purple plague), which has caused serious damage to the ecosystem of Tahiti in French Polynesia. It has also escaped in Hawaii and is the subject of an intensive and costly eradication effort there. Recently it was discovered in Queensland, Australia, and has spread to other islands in French Polynesia.

Melinis minutiflora (molasses grass), a species that is both invasive and causes a serious fire hazard. It has fostered the establishment of fire regimes on many islands where it has been introduced. It is cited in the literature as being present but not weedy in Samoa, and is present on a number of other Polynesian islands. It is not recorded from American Samoa, but even though it may not be causing problems in Samoa, it is a species that it would be desirable to exclude, given its reputation.

Passiflora tarminiana (banana poka, formerly known as P. mollissima), a smothering vine that is a problem in Hawai‘i and New Zealand.

Pennisetum setaceum (fountain grass), another grass that is a major problem in Hawai’i. It is recorded as being present in Fiji.

Psidium cattleianum (strawberry guava), a small tree that forms dense thickets and is a major problem species in Hawai‘i, Tahiti and elsewhere.

Rubus species (blackberries and raspberries), many of which are pests.

Tibouchina herbacea (glorybush or cane ti), another species that is a major problem in Hawai‘i.

And the above are just the worst of the lot. In addition, all grasses, all members of the Melastomataceae family, and all Ligustrum, Passiflora or Rubus species not already present should be highly suspect and should be proven benign before they are allowed to be introduced.

The best indicator that a species might be invasive is the fact that it is invasive elsewhere. However, each island ecosystem is unique, and invasiveness cannot be predicted with certainty. A good strategy is to be extremely cautious and exclude those species known to be invasive or weedy elsewhere (although an even better strategy, now being adopted by countries such as Australia and New Zealand, is to exclude all species not shown by risk analysis to be of negligible risk). Known problem species that have the potential to cause problems in tropical island ecosystems are listed in Appendix 2, Table 1. These species should be excluded through plant quarantine and, if establishment is detected, promptly evaluated for eradication.

In addition, there are a number of species that are present on Tutuila that are not present on Ofu, Olosega, or Ta‘u (see Appendix 3). Measures that limit the spread of invasive species to these islands, or prompt eradication, may keep these islands free from some pests already on Tutuila.

2. Species that are invasive elsewhere and are likewise invasive or have the potential to become so in American Samoa

Some known invasive plants that are causing trouble in similar ecosystems have been introduced into American Samoa (see Appendix 2, Table 2). Some of them are already causing problems while others are not. Some are cultivated plants that have not (yet) escaped and their potential for causing damage is so far unknown. However, one of the best predictors of invasiveness is the behavior of the species elsewhere, and these are known troublemakers.

Adenanthera pavonina (the coral bean tree, lopa) is invasive in secondary forests, but also has the ability to become much more widely established, both on Tutuila and the Manu‘as. On Ofu it was invading relatively intact forest margins, producing what seemed to be an overwhelming number of seedlings. It has probably spread too widely for anything but local control in sensitive areas but this should certainly be explored. Unfortunately, many people roast and eat the seeds, refering to them as "Samoan peanuts", and don't view the tree's presence as a problem.

Antigonon leptopus (chain of hearts) is reported to be present on Tutuila. This climbing vine has become a widespread pest on Guam. It has not yet escaped cultivation in American Samoa. It should be observed for invasive behavior on Tutuila and excluded from the outer islands.

Bryophyllum pinnatum (life plant), probably also an escape from cultivation, was seen on both Tutuila and Olosega. It reproduces vegetatively and may be invasive on the forest floor.

The Panama rubber tree (Castilla elastica, pulu mamoe), previously reported to be highly invasive in Samoa, has become established on Tutuila near Maloata. It is also reported to be found near 'Ili'ili. This species has the ability to become established in intact forests, posing a threat to the native forests. It presently doesn't seem to be too widespread and might be a good candidate for eradication or control.

Cinnamomum verum (cinnamon, tinamoni) is actively naturalizing in secondary forests in several locations on Tutuila. It shows great potential for becoming a major invasive species. It should be evaluated for control measures and should be excluded from the Manu‘a islands.

Clerodendrum chinense (Honolulu rose, losa Honolulu) is prevalent on both Tutuila and the Manu‘a Islands. This shade-tolerant species reproduces from root suckers.

Clidemia hirta (Koster’s curse) is present on Tutuila and the Manu‘a Islands (particularly on Ofu and Ta‘u). It is scattered and localized on Olosega. This species is a serious problem species in Hawai‘i. The thrips Liothrips urichi was introduced as a biological control agent on Tutuila about 25 years ago and seems to be giving a reasonable level of control. It was recently introduced to Ta‘u. The agent could also be introduced to Ofu/Olosega. Work is under way on additional bio-control agents in Hawai‘i.

Costus speciosus (crepe or wild ginger) was seen naturalizing on Tutuila. This is a potentially troublesome species that reproduces vegetatively and can grow in either full sun or shaded forest understories. At least in the A'oloau area of Tutuila it seemed to thrive in areas of disturbance (in this case an abandoned orchard that was being turned into pasture). It is a weedy species in French Polynesia.

Dieffenbachia seguine (spotted Dieffenbachia or dumb cane), which probably escaped from cultivation as an ornamental, was seen in a number of locations on Tutuila, including the National Park of American Samoa. This is potentially a very bothersome species, as it reproduces vegetatively and can thrive in the dense shade of an intact native forest canopy.

An isolated infestation of a Hedychium sp. (ginger) was seen on Ta‘u that should be promptly eradicated.

Imperata cylindrica (cogon grass) has been reported to be present in American Samoa. We did not see it, and it may not be a problem in American Samoan ecosystems, but this is a very invasive species elsewhere and, if found to be present, should be closely monitored for spread.

Lantana camara (lantana, latana) was observed being grown as an ornamental on Tutuila and Ta‘u. Although a serious pest elsewhere in the Pacific (and throughout the tropics), it does not seem be a problem here, at least yet.

Leucaena leucocephala (fua pepe), as is the case throughout most of the Pacific, is prevalent on all the islands.

A Ligustrum (L. sinense?) was noted in cultivation on Tutuila. Privets are notorious invaders and it would be desirable to eradicate any examples and exclude them in the future.

Lonicera japonica (Japanese honeysuckle) was also seen in cultivation on Tutuila and Ta‘u. This is another well-known invader. If possible, it should be eradicated or at least further plantings discouraged and the present ones monitored for spread.

Merremia peltata (fue lautetele) is quite invasive on Tutuila and is also found on Ta‘u. According to local sources, it was introduced about 1970, although this may just have been the time it became a noticeable problem. It is apparently a native or an early introduction throughout much of Melanesia, Polynesia and Micronesia, but its aggressive behavior has been noted elsewhere. Not seen on Ofu and Olosega.

Mikania micrantha (mile-a-minute weed, fue saina) has become well established as a major pest of disturbed areas on all the major American Samoan Islands.

Mimosa diplotricha [=invisa] (giant sensitive plant, vao fefe palagi) is established on Tutuila and Ofu, although not widespread. Given its limited extent on Ofu, it is a prime candidate for eradication there. It should be excluded from Olosega and Ta‘u and promptly eradicated if found. A biological control agent is available that might also be employed if M. invisa becomes more widespread. However, this agent (Heteropsylla spinulosa) will not eradicate the plant and is most effective in open areas, such as pastures.

Paraserianthes falcataria [Falcataria moluccana] (tamaligi palagi) is widespread on Tutuila. However, it may be a candidate for exclusion or control on the Manu‘a Islands.

Spathodea campanulata (African tulip tree) is present in cultivation on Tutuila. This tree has become a major problem in Fiji, the Hawaiian Islands and some other places. It is a problem species in Samoa and thus should be closely monitored for spread from its present locations in American Samoa. It was not observed on the Manu‘a Islands and it would be good to exclude it from there.

Syngonium angustatum, a climbing aroid, was seen spreading in the National Park of American Samoa along the Mount 'Alava trail. It was also noted in many areas bordering habitation sites (e.g. the Government housing area). This is an especially aggressive plant that has the ability to tolerate low light conditions such as those found in relatively intact forest settings. Along one area of the Mount 'Alava trail it completely dominated the groundcover layer, seemingly to the exclusion of all other species. It also has a tendency to climb and in fact was covering the trunks of most of the mature trees in the area. This species would probably require hand or mechanical removal, followed by periodic checks, for eradication. Syngonium is able to reproduce from a single node and almost certainly bits and pieces of the stems would be overlooked.

3. Species that are not known to be invasive elsewhere but have the potential to spread in American Samoa

A few species that have not been particularly invasive elsewhere have the potential to become problems in American Samoa (Appendix 2, Table 3).

Clerodendrum quadriloculare is suspicious because it appears to have the ability to invade intact or relatively intact native forests. This species is notorious for being a prolific producer of root suckers and in fact the plant is easily propagated by means of root cuttings. A dense, monospecific understory of this species was seen growing in full shade beneath the forest canopy on Pohnpei, making it a likely candidate to invade intact or only slightly disturbed native forest stands. Specimens observed on Tutuila and Ta‘u were cultivated ones in yards, but this species should be monitored for possible naturalization. If so, naturalized populations should be promptly eradicated.

Desmodium nicaraguense (synonym D. rensonii) has been distributed as a forestry tree but shows signs of naturalizing. It should be closely monitored and, if necessary, naturalizing populations controlled.

Flemingia macrophylla has likewise been distributed as a forestry tree and may naturalize. Again, close monitoring and, if necessary, control is in order. Another Flemingia species, F. strobilifera, is invasive on Tahaa and Raiatea (Society Islands) and naturalizes along roadsides on Nuku Hiva (Marquesas), French Polynesia, as well as in the Hawaiian Islands.

Sambucus mexicana (Mexican elder) is fairly common on Tutuila, both as an ornamental and naturalized in open areas. It is also present on Ta‘u.

The white-flowered form of Sesbania grandiflora (hummingbird tree) has naturalized in localities where it has been planted on Tutuila. It was originally introduced as a possible fuelwood tree, but it is not resistant to hurricanes. If not too widespread, it may be a candidate for control or eradication.

4. Species that are mentioned or listed as weedy or invasive elsewhere and are common or weedy in American Samoa

A large number of other common or weedy introduced species were noted. Many of these species, which might best be termed aggressive weeds, are mostly prevalent along roadsides or on disturbed sites, although some species, particularly alien trees, can gradually spread into forested ecosystems. In the case of vines and plants that form dense ground cover, the regeneration of native species can be inhibited.

Some of these species could become a problem in the future, since there is often a long lag time between introduction and when a species begins to cause serious impacts. These species (listed in Appendix 2, Table 4) should be seriously evaluated for inter-island quarantine to confine them to the islands where they are presently located or to eradicate them if they become established elsewhere.

Potentially invasive tree species include Acacia auriculiformis (earleaf acacia), A. mangium, Ceiba pentandra (kapok, vavae), Schefflera actinophylla (octopus tree), Syzygium jambos (malabar plum), Samanea saman (monkeypod), Tabebuia heterophylla (pink trumpet tree) and Tecoma stans (yellow bells).

Passiflora maliformis (pasio) is reported to be in American Samoa (not seen). This species is on the French Polynesia noxious weed list.

An isolated infestation of Solanum torvum (prickly solanum) is located on Tutuila and should be eradicated.

Likewise, an infestation of Ipomoea alba on Tutuila should be eradicated.

A wide variety of introduced grasses have become established, the most aggressive of which include Cenchrus echinatus (bur grass, vao tuitui); Cynodon dactylon (Bermuda grass); Paspalum spp., including P. conjugatum (Hilo grass, vao lima), P. dilatatum (Dallis grass), P. fimbriatum, and P. urvillei (Vasey grass); Pennisetum pupureum (elephant or napier grass) and Sorghum halepense (Johnson grass) (although there is some question as to the identify of this last species – Whistler (1988) classifies it as S. sudanense, a less aggressive species).

Other widespread weedy species include Indigofera suffruticosa (indigo), Mimosa pudica (sensitive plant, vao fefe), Passiflora foetida (love-in-a-mist, pasio vao), Psidium guajava (guava, ku'ava), Stachytarpheta cayennensis [urticifolia] (blue rat's tail, mautofu tala) and Wedelia [Spagneticola] trilobata (Singapore daisy, ateate). Derris malaccensis (New Guinea creeper, 'ava niukini) is present and invading lowland coastal forests on Tutuila, Aunu'u, Ofu and Olosega.

A number of other species present to some degree in American Samoa have bad reputations elsewhere. These should be monitored for invasive behavior and evaluated for quarantine. They include bamboos (Bambusa and other bamboo species), Cestrum diurnum (day cestrum) and C. nocturnum (night-flowering cestrum, queen of the night, teine o le po, ali'i o le po), Duranta repens (golden dewdrop), Hedychium spp. (gingers), Hemigraphis alternata, Hyptis pectinata (comb hyptis or mint weed), Ricinus communis (castor bean) and Schinus terebinthifolius (Christmasberry).

5. Native and naturalized species exhibiting aggressive behavior

Some native species (or early introductions) exhibit characteristics that could make them problem species if they are introduced to islands where they are not present. These species are listed in Appendix 2, Table 5.

Strategies for dealing with invasive species

The first line of defense against invasive species is to keep them out. Control at ports of entry is essential, and land management officials should work closely with plant protection and quarantine officials to make them aware of known and potential invasive plant species. Plant quarantine officers are familiar with most agricultural pests, but they may not be aware of some of the pests that threaten wildland ecosystems. In cooperation with the plant quarantine organization, a list of noxious species to be excluded should be developed and exclusion of these species should be backed by the force of law and regulation. Better yet is to go to the approach recently adopted by Australia and under serious consideration by a number of other counties. That is to exclude all alien species not shown to be of negligible risk. Risk assessment and management techniques can be used to assess the likelihood and effects of possible introductions and to develop exclusion and eradication strategies.

Other exclusion measures that would be desirable to put in place include:

Education of the public about the danger of introductions and encouraging the use of native species can be helpful. What may just be a pretty flower to be planted in a yard or garden can turn out to be an invasive species. It is particularly important to work with local nurseries and botanical gardens, as these are often sources of new introductions. A positive approach is to work together to develop a "white list" of both native and non-native species that the public can be encouraged to plant.

The public also needs to understand that the immediate eradication of a small area of a problem species, even if it involves the use of herbicides, may be better than living with a problem species forever. There are many instances where you hear people say "I wish we'd taken action when this pest was first noticed". It may even be worthwhile to take people to a place where they can be shown the full extent of the problem if the infestation is allowed to spread so that they will accept and support eradication. For example, anyone visiting Tahiti would very likely come away convinced that Miconia calvescens is an ecological disaster and that it should be prevented from becoming established on other Pacific islands.

The public should also be encouraged to report suspicious plants. Public service announcements on television or radio or newspaper articles can encourage this. Funding can be requested to prepare PSA's or "wanted" posters. Prompt follow-up to public reports is essential to maintain the credibility of such a program.

Land managers and extension agents should be alert to new species that exhibit invasive behavior. Often, these species first show up in urban or farm areas because they are usually introduced by people and tend to become established in disturbed areas. Suspicious plant species should be promptly reported. A scouting program should be established where scheduled surveys are made for new or expanding infestations. A formal evaluation should be requested for any new species that appears to be invasive or is known to be invasive elsewhere. This evaluation should be by an expert who is familiar with the species and methods for its eradication or control and can recommend further action. Prompt action is essential, since once a species becomes widespread, control or eradication can be extremely costly or impossible.

It is also very helpful to have laws and regulations in place to aid in dealing with new introductions. This includes the ability of government to require the control of noxious species on private lands or to take action on private lands if the landowner cannot be located or does not take prompt action. Provision for emergency funds to deal with immediate problems should also be in place. Model laws and regulations can be obtained from states and countries that have implemented them.

The American Samoan government is encouraged to take advantage of the Federal assistance programs in dealing with invasive plant species. American Samoa is already utilizing cost-share funding to provide locally available expertise in forest health protection. Experts are also on call from the Forest Service’s Forest Health Protection staff, or they can arrange for expert consultation. Finally, cost-share funding can be requested to deal with forest health problems, including plant pests, under the Cooperative Forestry and Hawaii Tropical Forestry Recovery acts. Funding is subject to recommendations resulting from a professional evaluation of the problem and the overall availability of funds. Funding also tends to be prioritized based on an economic evaluation of cost-effectiveness, so rapid eradication of a pest species while it is still confined to a small area would undoubtedly take precedence over the chronic problem of a species that has escaped control.


In addition to the above strategies, we offer the following specific recommendations.

All islands:


Manu‘a Islands:

Probably because of their isolation, these islands have fewer weed species than Tutuila. For example, Mimosa diplotrichais apparently not present on Ta‘u. While inter-island quarantine inspection is probably not realistic, some measures could be instituted to reduce the risk of introduction or establishment of weed species not already present. These include cleaning road construction equipment before it is moved between Tutuila (or other locations) and these islands, public education and reporting of problem species, scouting expeditions to discover incipient infestations, and prompt eradication of new infestations.

Recommendations for the individual islands follow.




Appendix 1   References

Appendix 2   Species by category

Appendix 3   Invasive and potentially invasive species present on Tutuila

Appendix 4   Invasive and potentially invasive species present on Ofu

Appendix 5   Invasive and potentially invasive species present on Olosega

Appendix 6   Invasive and potentially invasive species present on Ta‘u

(1)  Former Director, Pacific Southwest Research Station, USDA Forest Service (now retired) and Curator of the Herbarium, National Tropical Botanical Garden, respectively.

(2)  Space, James C. and Marjorie Falanruw (1999). Observations on invasive plant species in Micronesia. Report prepared for the meeting of the Pacific Islands Committee, Council of Western State Foresters, Majuro, Republic of the Marshall Islands, February 22-26, 1999.

(3)  We would like to thank Colin Steele,  Acting Forestry Program Manager, and Manu Tuiono'ula, Forest Health Coordinator, American Samoa Community College Land Grant, for their generous assistance in the conduct of the survey. We would also like to thank Pa'u Young for his assistance in our survey of Ta‘u.

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This page updated 11 March  2000.