Bidens meyeri (Asteraceae/Compositae) is described and illustrated from Rapa, Austral Islands, (French Polynesia). This new species is presumed to be most closely related to Bidens saint-johniana from nearby Marotiri Island. Bidens meyeri may be distinguished from B. saint-johniana based on the length of the peduncle (3 cm versus 10 cm), apex of the inner involucral bracts (glabrous vs. puberulent), smaller leaves (2.0–2.3 cm vs. 5–6 cm), and the general smaller size of the new species. Known from less than 50 individuals and restricted to one remote location, Bidens meyeri falls into the IUCN Critically Endangered (CR) category. The new species is named in honor of Dr. Jean-Yves Meyer, Délégation à la Recherche, Polynésie Française,

Asteraceae , Austral Islands, Bidens , Coreopsideae , Compositae , conservation, endemic, French Polynesia, IUCN Red List Category, Oceania, Rapa Iti.

The Austral Islands are situated in the Southern Pacific and are part of French Polynesia. The Archipelago lies south of the Society Islands and consists of seven main islands of volcanic origin, and one atoll (Maria). The high islands include Rurutu, Tubuai, Rimatara, and Ra’ivavae as well as Rapa (27°36'00"S; 144°17'00"W), the second largest island (i.e., 40 km²). Rapa is about 5 million years old and it is very rugged, characterized by steep central ridges, mist shrouded spires, and towering black basalt sea-cliffs (Clarke 1971, Clouard and Bonneville 2005, Appelhans et al. 2014). The highest peak, Mont Perau (ca. 650 m), is covered by a small area of cloud forest (Meyer 2010).

Rapa is a high volcanic island and its climate is considered to be wet subtropical / subtemperate with a mean annual temperature of 20.6°C, a minimum at 8.5°C, and mean annual rainfall of 2500 mm at sea level (Barsczus 1980; Meyer 2011). Levels of endemism have been reported as very high among certain organisms, such as weevils (Paulay 1985). Area, altitude, and nearest land mass all have an effect on the evolution of the biota in these islands with Rapa being the second largest, highest, and most distant of all of the Austral islands. It is nearly 1200 km southeast of Tahiti, 3700 km northeast of the north island of New Zealand, and 8500 km southwest of the Baja Peninsula in Mexico. Threats to the biodiversity are primarily a result of burning, grazing (in particular goats and cattle), and invasive alien plant species.

Rapa has 238 native taxa of flowering plants and ferns including infraspecific categories, 85 of these are endemic to the Austral islands (35%), 73 of these are single island endemic taxa (30%) including this new species of Bidens. Considering only flowering plants, Rapa has 152 native flowering plant taxa, of these 65 (43%) are endemic to the Austral islands and 53 (35%) are endemic to Rapa (Meyer 2002, Wood 2002, Wood pers. com.). Two island endemic genera in the Compositae have been reported: Apostates N.S. Lander in the Madieae tribe, part of the Heliantheae Alliance, and Pacifigeron G.L. Nesom in the Astereae. Also, there are endemic Compositae species on Rapa that belong to two ‘endemic to Polynesia’ genera, namely Fitchia Hook. f. and Oparanthus Sherff both in the Coreopsideae tribe which is also part of the Heliantheae Alliance (Florence 1997, Shannon and Wagner 1997, Wagner and Lorence 2011).

In March – April 2002, during an expedition supported by the National Geographic Society, a group of scientists from the New York Botanical Garden (NYBG); the Délégation à la Recherche, Polynésie Française; and the National Tropical Botanical Garden (NTBG), Kaua`i, Hawai`i, conducted a botanical survey of the island of Rapa. They expected to stay there for a month. In fact, because of a logistic problem that delayed the supply ship (their means of transportation), several of them stayed for two months. During this Rapa expedition a number of very interesting taxa were discovered, one of which was a Bidens that could not be placed into any existing species (Fig. 1; Meyer 2002, Wood 2010).

Describing this taxon was unusually difficult because of the scant material (Fig. 2a, b). Other samples were collected during the expedition but are inaccessible. The collector of the holotype specimen gathered several isotypes that would have been sufficient, however, all except the small one he retained (the type) have evidently been misplaced and with the untimely death of the expeditions team leader, Dr. Timothy Motley (NY followed by ODU), the specimens have not been available for study. On a subsequent expedition in December of 2002, an additional collection was made by Jean-Yves Meyer close to the original location (Meyer 2315; Fig. 1). Meyer’s collection was sent to the Paris herbarium (P) but cannot now be located (Meyer, pers. com.). After waiting for over ten years we have decided to go forward with the description of this new taxon as it is being included in a forthcoming molecular analysis and needs to be recognized for future conservation efforts. The leaf sample for the molecular analysis was taken from the holotype, prior to its designation as a holotype, with permission from the National Tropical Botanical Garden.

Figure 1. 

Photos of Bidens meyeri: A Close up of a flowering plant, note the gloved finger holding the plant B J-Y Meyer climbing with Bidens in his teeth, note yellow flowering plant on the cliff face just above his left hand. [Photo credits: A by J-Y Meyer; B by R Englund; both taken 16 Dec 2002].

Figure 2. 

Photos of Bidens type specimens: A–C Bidens meyeri holotype (PTBG): A–B Specimen before mounting A Side with the involucral bracts and (mostly) upper surface of the leaves showing B Side with the flowers and (mostly) the undersurface of leaves showing C Holotype of Bidens meyeri, housed at PTBG D Holotype of Bidens saint-johniana, housed at BISH. [Photo credits: A–C by Jesse Adams, PTBG; D sent by BISH].

The only other native species of Bidens from the Austral Islands is B. saint-johniana Sherff (1937) found on Marotiri, a group of small rocky islets located ca. 80 km southeast of Rapa. Marotiri has been surveyed only twice by botanists: St. John and Forges. Bidens saint-johniana was first collected at the Southeast Islet, 22 July 1934, by Harold St. John (Fosberg 1972; St. John 1982) and his assistant at the time, Ray Fosberg (St. John 15683; holotype: BISH; isotype F, http://plants.jstor.org/specimen/f0075334f?history=true; images of both were examined; Fig. 2D), and again in 1979 by B. Richer de Forges (Nicolas Hallé 6860, P; Hallé 1980). Bidens saint-johniana is a much more robust plant than B. meyeri, its leaves are larger (total length 5–6 cm, width at the widest part 3.5–4.0 cm) and peduncle longer (10 cm vs. 3 cm), and the apex of the inner involucral bracts is puberulent (vs. glabrous). Based on the images of the holotype (BISH; Fig. 2D) and isotype (F) the leaves are not thickened and the teeth are larger and not as curved and do not have a mucronate tip. Finally the length of the side branches was 14–15 cm as opposed to those of B. meyeri which are less than 8 cm.

When the new species was run through the key in the Bidens treatment written by Welsh (1998) covering the Society Islands, it did not key out to anything remotely similar and it did not fit any of the descriptions. It does, however, have some superficial resemblance to B. molokaiensis Sherff and B. mauiensis Sherff from Hawaii, as Sherff (1937) observed.

Rapa’s flora is usually mentioned as being closely allied to that of New Zealand and Australia. However, after evaluating the results of numerous exceptions, some botanists (e.g., van Balgooy 1971) consider Rapa to be an ‘anomalous district’ in the SE Polynesian Province, and the high levels of endemic biological diversity in both the flora and fauna still puzzle many scientists because of the island’s relatively small size. There are 53 flowering plant species (35%) that are single island endemics to Rapa, including three endemic plant genera, namely Apostates (Asteraceae: Bahieae), Pacifigeron (Asteraceae: Astereae) and Metatrophis F. Br. (Urticaceae). The new species is clearly related to the Pacific Bidens radiation (Hawaii & French Polynesia) rather than taxa found on Rapa’s neighbors to the South.

Utilizing the World Conservation Union (IUCN) criteria for endangerment (IUCN 2001), we find that Bidens meyeri easily falls into the Critically Endangered (CR) category, and faces a very high risk of extinction in the wild. The IUCN alphanumeric summary of our evaluation of criteria and subcriteria is: B1ab(v); B2a, B2b(i–iii); D. These criteria are defined as: B1, extent of occurrence less than 100 km²; B1a, known to exist at only a single location; B1b(v) continuing decline inferred in number of mature individuals; B2, total area of occupancy less than 10 km²; B2a, one population known; B2b(i–iii), habitat continuing decline inferred; D, population estimated to number fewer than 50 individuals. Threats to B. meyeri include possible fires, habitat degradation and destruction by feral goats (Capra hircus L.), along with competition with non-native plant taxa especially Psidium cattleianum Sabine and, of course, climate change.

We would like to thank Jean-Yves Meyer and Priscille Frogier of the Délégation à la Recherche de la Polynésie Française, for their support of research in French Polynesia; Staff at the National Tropical Botanical Garden for continued support and assistance at the PTBG herbarium, especially Tim Flynn, Dave Lorence, and Jesse Adams; Timothy J. Motley† (NYBG at the time of the expedition), organizer of the 2002 Rapa Expedition, and the National Geographic Society for partial funding; Steve Perlman (NTBG), Jean-Francois Butaud (Service du Développement Rural, Tahiti), Cerdan and Heimoana Faraire (Rapa) for field assistance. We also thank Jean-Yves Meyer, Ron Englund, and Jessie Adams for the photographs, Alice Tangerini (US) for helping assemble Fig. 2, Shelly James (BISH) who kindly made available a high-resolution image of the holotype of B. saint-johniana, and the herbarium of the Field Museum (F), and JSTOR Global Plants Initiative for putting the image of the isotype online.