by Jean-Yves Hiro Meyer, Délégation à la Recherche (Tahiti, French Polynesia); Darko D. Cotoras, Pontificia Universidad Católica de Chile & California Academy of Sciences; Pedro Lazo Hucke, CONAF Provincial Easter Island; Sebastián Yancovic Pakarati, Manu Project, Koro Nui o te Vaikava, CAMN Rapa Nui
The flora of Motu Motiro Hiva is as scarce as it is fascinating, and understanding it starts with placing this island on the map. Motu Motiro Hiva is considered one of the most isolated islands in the world. It lies about 400 km east of Rapa Nui (Easter Island), 2,500 km west-northwest of the Juan Fernández Archipelago, and 3,400 km from Chile’s northern coast. This extremely remote, uninhabited island is considered the easternmost point of the “Polynesian Triangle,” a cultural and linguistic region comprising Hawai’i to the north, Aotearoa (New Zealand) to the southwest, and Rapa Nui to the southeast. The first Europeans to sight Motu Motiro Hiva were the Spanish navigators José Sálas Valdés in 1793 and José Manuel Gómez in 1805, which explains the name Salas y Gómez Island.
An island born from the ocean floor
The island is the summit of a large seamount that rose roughly 3,500 m from the ocean floor nearly two million years ago. It is very small, with a land area of about 15 ha and a maximum elevation of 30 m, shaped like a horseshoe formed by two small bare rock hills joined by a narrow isthmus, with a sandy depression roughly 70 m in diameter at the center of the westernmost sector. You can read more about its geological origin in Motu Motiro Hiva’s most beautiful secret.
A fauna far richer than its flora
Motu Motiro Hiva is well known among biologists for its large seabird colonies. A total of 20 species have been recorded, at least 10 of which have been observed breeding or nesting, including the Christmas shearwater Puffinus nativitatis, the brown noddy Anous stolidus, the sooty tern Onychoprion fuscatus, the black noddy Anous albivitta, and the polynesian storm petrel Nesofregetta fuliginosa, whose nearest colonies are 2,400 km away in Gambier and 3,400 km away in Rapa Iti (French Polynesia). The island is also recognized as an important area for shark conservation in this part of the Pacific.
Recent entomological studies on Motu Motiro Hiva have also shown the richness of its terrestrial arthropods, echoing what has already been documented about the endemic arthropods of Rapa Nui. At least 15 morphospecies were collected, including two moth species and two species of isopods (small terrestrial crustaceans). Among the arachnids, an endemic spider, Ariadna motumotirohiva, morphologically close to Ariadna perkinsi from Hawai’i and Ariadna lebronneci from the Marquesas, was recently described (Giroti et al., 2020). In addition, Hawaiioscia rapui, an isopod first described from caves in Rapa Nui and belonging to a genus known only from the Hawaiian Islands and a few localities on the Costa Rican coast, was found in 2016.
The flora of Motu Motiro Hiva: four species for science
The vascular flora remained known only from scattered mentions until the authors’ own publication in 2023 (Meyer et al., 2023). The first naturalists to land on Motu Motiro Hiva attributed its sparse vegetation to its small size and low elevation, exposed to partial flooding and sea spray during swells and storms. Swedish botanist Carl Skottsberg reported in 1956 that “a halophytic Asplenium is the only living thing observed on the distant reef of Sala y Gómez.” Based on photographs taken during several expeditions between 2011 and 2022, we were able to identify four different plant species.
A fern with Polynesian roots
First, the small fern with leathery fronds Asplenium obtusatum var. obtusatum (Aspleniaceae), known from the east coast of Australia, New Zealand, some islands of southeastern Polynesia (the Society, Gambier, and Austral Islands of French Polynesia, and the Pitcairn Islands), as well as Rapa Nui, the Juan Fernández Archipelago, and South America (Figure 1).
Two succulent herbs of tropical coastlines
The second species was the succulent herb Portulaca oleracea (Portulacaceae), with a thick, fleshy stem and small bright yellow flowers (Figure 2). It is a pantropical species, presumably native to the Old World (Africa, the Mediterranean, or southern Asia), and a modern introduction in western and eastern Polynesia. It is considered native or a doubtful native species on Rapa Nui.
The third plant species is the succulent herb Sesuvium portulacastrum (Aizoaceae), with stems ranging from red to green and red-pink-lavender-white flowers forming dense clusters (Figure 3). It is a pantropical coastal species found in South America, Caribbean islands, South Pacific islands including eastern Polynesia, and the Hawaiian Islands. It is one of the few flowering plants capable of growing in a habitat flooded with salt water at every high tide. We consider this species native to Motu Motiro Hiva.
A species new to science
Finally, we found a new island record that we consider new to science: a small succulent herb (< 20 cm) with fleshy square stems, fleshy sessile to subsessile obovate leaves with a pronounced midrib, and small corolla-less flowers borne in short axillary inflorescences (Figure 4). This species is related to, but clearly distinct from, Parietaria debilis (Urticaceae), an annual erect herb with non-fleshy stems and leaves, native to Australia, New Zealand, the Juan Fernández Archipelago, San Ambrosio Island (Desventuradas Islands), and the Galápagos Islands. In New Zealand, P. debilis has been reported on the Kermadec, Three Kings, and Chatham islands, typically found in coastal scrub and forest around petrel or shearwater burrows, sometimes growing on exposed rocks or sand dunes.
A unique ecosystem that deserves protection
Motu Motiro Hiva holds a surprisingly poor flora compared to its relatively diverse avifauna and arthropod fauna. Its terrestrial flora and fauna show connections to Rapa Nui, its nearest island, but also to other remote Pacific island groups such as the Marquesas or Hawai’i. The presence of an undescribed Parietaria points to floristic relationships with islands off the coast of South America, particularly the Juan Fernández Archipelago, the Desventuradas Islands, and the Galápagos. This unique island ecosystem deserves continued protection efforts, especially against the impacts of climate change, including sea level rise. This constant dynamic of species arriving, adapting, or disappearing is part of what we explore in everything is in motion: an island in the middle of the ocean, as well as in the case of newly arrived species such as Watersipora subtorquata.
Frequently asked questions about the flora of Motu Motiro Hiva
How many plant species have been identified on Motu Motiro Hiva?
Four species have been identified: the fern Asplenium obtusatum var. obtusatum, the succulent herbs Portulaca oleracea and Sesuvium portulacastrum, and a Parietaria species not yet described to science.
Why is the flora of Motu Motiro Hiva so poor?
Its small size, low elevation, and exposure to partial flooding and sea spray during swells and storms severely limit which plants can establish themselves, unlike its much more diverse avifauna and arthropod fauna.
What is Motu Motiro Hiva’s relationship to Rapa Nui?
Rapa Nui is Motu Motiro Hiva’s nearest island, about 400 km away, and shares floristic and faunistic connections with it, though Motu Motiro Hiva also shows links to the Marquesas, Hawai’i, and archipelagos off South America such as Juan Fernández and the Galápagos.
Where is Motu Motiro Hiva located?
It lies 400 km east of Rapa Nui, 2,500 km from the Juan Fernández Archipelago, and 3,400 km from Chile’s northern coast, at the easternmost point of the Polynesian Triangle.
