Bidens meyeri (Asteraceae, Coreopsideae): a new critically endangered species from Rapa, Austral Islands

Abstract 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 Bidens 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,


Introduction
Th e Austral Islands are situated in the Southern Pacifi c and are part of French Polynesia. Th e Archipelago lies south of the Society Islands and consists of seven main islands of volcanic origin, and one atoll (Maria). Th e 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 km 2 ). Rapa is about 5 million years old and it is very rugged, char-acterized by steep central ridges, mist shrouded spires, and towering black basalt seacliff s (Clarke 1971, Clouard and Bonneville 2005, Appelhans et al. 2014. Th e 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 eff ect 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. Th reats 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 fl owering plants and ferns including infraspecifi c 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 fl owering plants, Rapa has 152 native fl owering plant taxa, of these 65 (43%) are endemic to the Austral islands and 53 (35%) are endemic to Rapa (Meyer 2002, Wood 2002. Two island endemic genera in the Compositae have been reported: Apostates N.S. Lander in the Madieae tribe, part of the Heliantheae Alliance, and Pacifi geron 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 2014.
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. Th ey 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 diffi cult because of the scant material ( Fig.  2 a, b). Other samples were collected during the expedition but are inaccessible. Th e collector of the holotype specimen gathered several isotypes that would have been suffi cient, 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 eff orts. Th e 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.

Taxonomic treatment
Bidens meyeri V.A. Funk & K.R. Wood, sp. nov. urn:lsid:ipni.org:names:77142603-1 Fig. 2A Description. Sub-shrub with 3-4 branches growing on cliff faces, ca. 25 cm tall, small side branches ca. 8 cm tall; stems brown, glabrous, lower portion smooth, upper portion striated, ca. 1 mm wide (when dry), glabrous, older nodes with the remains of leaf bases. Leaves opposite, simple, somewhat fl eshy, glabrous, without true petioles but looking petiolate because of narrowed blade bases, 2.1-2.3 cm long; broad part of leaf ovate, glossy green above, dull green below, 1.1-1.5 cm long × 1.0-1.2 cm wide; margins of broad part of leaf dentate with teeth curved toward apex and with mucronate tips, 6-9 teeth per side; apex mucronate or apiculate; venation pinnate usually with one lateral vein for each tooth; narrow portion of leaf ca. 1 cm long decurrent with leaf bases wrapping around stem and nearly touching one another. Heads solitary, ~ 1 cm in diameter (excluding rays), peduncle 3 cm long, glabrous with prominent ribs (when dried); involucral bracts in 2-3 rows, outer two rows bright green, purple tipped in some, slightly fl eshy, glabrous with 3 prominent veins (when dried), arched outward, ca. 5 mm × 1.3 mm (at the broadest point near the apex), apex rounded with a small acute tip; innermost row (may also be outer row of receptacular bracts) lanceolate, brownish with lighter hyaline margins, glabrous, 5.5 mm × 1.1 mm (at widest point near the base). Ray fl owers yellow with many veins, 8-9 per head, sterile, ca. 9 mm long (including 2 mm tube) × 1.5-2.0 mm wide; disk fl owers ca. 30-40, perfect; corollas yellow, glabrous; anther thecae dark, pollen yellow; style branches yellow. Pappus of 2 very short irregular awns with scattered hairs but without barbs. Achenes immature but apparently dark colored and glabrous, at least near the apex.  Distribution and ecology. Th e type of Bidens meyeri was discovered during a rappel utilizing ropes and climbing-saddle around the windswept mesic cliff s above Maitua, Rapa, French Polynesia. Th e holotype location is the only population of any size; the second collecting site had only two individuals. Th e type locality can be described as a windswept mesic cliff habitat with small ledges and pockets of granular Etymology. Th e new species is named in honor of Dr. Jean-Yves Meyer, friend and conservation biologist at the Délégation à la Recherche, Polynésie Française, in recognition of his research of this species and his eff orts in exploring and conserving the unique biota of Rapa (e.g., Meyer 2011).

Discussion
Th e 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 fi rst collected at the Southeast Islet, 22 July 1934, by Harold St. John (Fosberg 1972St. 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 fi t any of the descriptions. It does, however, have some superfi cial resemblance to B. molokaiensis Sherff and B. mauiensis Sherff from Hawaii, as Sherff (1937) observed.
Rapa's fl ora 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 fl ora and fauna still puzzle many scientists because of the island's relatively small size. Th ere are 53 fl owering plant species (35%) that are single island endemics to Rapa, including three endemic plant genera, namely Apostates (Asteraceae: Bahieae), Pacifi geron (Asteraceae: Astereae) and Metatrophis F. Br. (Urticaceae). Th e new species is clearly related to the Pacifi c Bidens radiation (Hawaii & French Polynesia) rather than taxa found on Rapa's neighbors to the South.

Conservation status
Utilizing the World Conservation Union (IUCN) criteria for endangerment (IUCN 2001), we fi nd that Bidens meyeri easily falls into the Critically Endangered (CR) category, and faces a very high risk of extinction in the wild. Th e IUCN alphanumeric summary of our evaluation of criteria and subcriteria is: B1ab(v); B2a, B2b(i-iii); D. Th ese criteria are defi ned as: B1, extent of occurrence less than 100 km 2 ; 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 km 2 ; B2a, one population known; B2b(i-iii), habitat continuing decline inferred; D, population estimated to number fewer than 50 individuals. Th reats to B. meyeri include possible fi res, habitat degradation and destruction by feral goats (Capra hircus L.), along with competition with nonnative plant taxa especially Psidium cattleianum Sabine and, of course, climate change.