The Flora of Samoa includes species of plants found in Samoa and American Samoa. The volcanic islands of Savaiʻi and Upolu comprise approximately 90% of the total land area of the country. The flora comprises about 550 native species of flowering plants, these species fall into 95 plant families and about 300 genera.^[1] In total, there are 833 native and naturalized flowering plants, and 225 ferns and allies. 177 are endemic.^[2] The diversity is approximately one-third the size of Fiji's flora, though the two regions share significant floristic affinities due to geographical proximity. In the islands, the largest family of flowering plants is Orchidaceae (orchids), which includes 101 native species. This represents the highest diversity of orchid flora among all Polynesian islands. The second largest family is Rubiaceae (the madder or coffee family), comprising 47 native and five naturalised species.^[3]

The Samoan Islands have many different vegetation zones, mainly composed of lowland rainforest, montane, and cloud forests. There are also swamp forests, mangrove forests, littoral scrub, and volcanic scrub.

The lowland rainforest is mostly supported by species such as Diospyros, Calophyllum, Dysoxylum, Pometia, Planchonella, Syzygium, and Myristica.^[4]

Lower mountain slopes support montane rain forests, which have a cooler and wetter climate than the lowlands. They support species in the genera Dysoxylum, Syzygium, Weinmannia, Canarium, and Astronidium.

Cloud forests typically grow at elevations higher than 650 metres (2,130 feet). These forests occurs at the highest elevations on the biggest islands of Savai'i and Upolu. They are filled with tree genera, such as Polyscias, Weinmannia, and Dysoxylum, as well as a few Cyathea plants.^[4]

The upland swamp forest is the rarest vegetation community in the country with only one area remaining.^[5] Upland swamp forests grow in wet, freshwater soil. They can be found near the coast and further inland. On the south coast of Upolu island, these forests are mostly made up of Inocarpus fagifer trees, while the west coast has scattered Erythrina fusca trees. Inland, swamps form in low basins and volcanic craters that do not drain well. The Fogalepolo crater in eastern Upolu has Pandanus tectorius trees in the middle and Barringtonia samoensis trees around the edge. There are other large swamp forests in eastern Upolu, but scientists have not yet studied their mix of plants.^[6]

Littoral scrub is a coastal vegetation type that grows on both sandy and rocky substrates, typically occurring between the herbaceous strand zone and littoral forest or Pandanus scrub. The community is generally dominated by Scaevola taccada, and Wollastonia biflora. Other characteristic species associated with this habitat include Clerodendrum inerme, Colubrina asiatica, Ficus scabra, and Premna serratifolia.^[6]

Mangrove forests are dominated by Bruguiera gymnorhiza that typically occur in sheltered coastal bays and estuaries featuring freshwater inflows. These habitats are subject to regular inundation by tidal saltwater or brackish water, as well as periodic freshwater flooding. The dense canopy heavily shades the understory, restricting regeneration primarily to Bruguiera seedlings, although canopy gaps host populations of the swamp fern (Acrostichum aureum) and Rhizophora samoensis. On the southern coast of Savai‘i, Bruguiera forests also associate with Xylocarpus moluccensis, a species considered rare within Samoa.^[6]

The volcanic scrub of Savaiʻi is a pioneer rainforest ecosystem found on historical lava surfaces formed between 1750 and 1911. The lowland subtype occurs at elevations of approximately 200 m (660 ft) and exists alongside a separate montane subtype. This lowland zone is characterized by emerging trees such as Fagraea berteroana and Glochidion ramiflorum, the shrub Morinda citrifolia, and fern species including Davallia solida and Nephrolepis hirsutula.^[6] The montane subtype of the volcanic scrub spans higher elevations with distinct vegetative zones. At 700 m (2,300 ft), the canopy includes the trees Metrosideros collina and Weinmannia samoensis alongside species from the genera Fagraea and Glochidion. A higher zone at 1,500 m (4,900 ft) is dominated by Samoan endemics such as Coprosma strigulosa, Spiraeanthemum samoense, and Vaccinium whitmeei. Localised ash plains also occur at this upper elevation, which lack shrub cover and are dominated exclusively by the grass and various lichens.^[6]

Since human arrival approximately 3,000 years ago, over 80 percent of the lowland rainforest has been destroyed. Unregulated logging and land clearing for subsistence and commercial agriculture have been the primary drivers of this ecological decline. On the heavily populated island of Upolu, nearly all accessible lowland, montane, and cloud forests have been entirely cleared. Environmental pressures were further aggravated by two severe cyclones in 1990 and 1991, which killed 53 percent of native forest trees.^[7] threats can also include cyclones, tsunamis, droughts, and barely fires. Little can be done to stop them since plants of the islands have endured this for many years, but they have gotten used to them and have always surrvived or at least have dealed with them.^[8] 15 species of plant endemic to Samoa are on the IUCN Red list that are considered endangered or threatened

About 40% of flowering plants in the country are introduced. Invasive plant species include the native Merremia peltata (fue lautetele) Castilla elastica (African Rubber tree), Cordia alliodora (salmwood) Spathodea campanulata (African tulip tree) and Hyptis pectinata. Some species are native to the country while others had been purposely introduced or accidental. 50% of all lowland rainforest in the country is dominated by the Merremia peltata. There are also feral goats, and Myna birds which cause impact in the forests.^[9] the Rattan palms are also invasive in the ecosystem, despite being native to the islands around the country. contributes to forest degradation and habitat loss by damaging surrounding vegetation and disrupting natural forest regeneration. They came in the 1990s as part of a cane furniture project. Additionally, the plant's sharp spines present a physical hazard to humans navigating the forest undergrowth, as they can easily snag clothing and skin.^[10]

Development of the Art Whistler Memorial Garden for rare and threatened plants began in 2019, and the facility was formally opened in 2021 by Samoan Prime Minister Fiamē Naomi Mata’afa. Established in memory of Arthur Whistler, an ethnobotanist who specialized in Samoan flora, the garden preserves more than 10 of the country's rare and threatened plant species. Many of these plants are endemic to the islands, such as the pau (Manilkara samoensis), which natively grows only on Savai'i.^[11] The Samoa Conservation Society collects plants on places such as Mount Le Pue, Mount Vaivai, and Malololelei on Upolu, alongside Mount Matavanu, Safotu, Falealupo, and Aopo on Savai'i. The initiative focuses on rare endemic species, as well as non-endemic plants, medicinal plants such as matalafi (Psychotria insularum), and butterfly-hosting species like talafalu (Micromelum minutum). These specimens are relocated to the Vailima Botanical Garden for preservation and public education. The project builds community capacity by supporting village-led nurseries in the villages, with plans to expand local propagation efforts to more villages in the future.^[12]

Many of the native flora came from Southeast Asia and New Guinea.^[13] There are some exceptions, such as the Vaccinium whitmeei, a species of the Ericaceae family, which is endemic to Savai'i, which may have origins from the temperate Americas, as well as Rhizophora mangle, Gyrocarpus americanus, and Abutilon whistleri.^[14][15][8]

• Samoan tropical moist forests
• List of endemic plants of Samoa
• List of Samoan plant common names

• Whistler, W. Arthur (2022). Lorence, David H.; Wagner, Warren L. (eds.). Flora of Samoa: Flowering Plants. Kauai, Hawaii: National Tropical Botanical Garden. ISBN 978-0-915809-04-2.

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