Melicope balgooyi Appelhans, W.L. Wagner & K.R. Wood, a new species and new record in Melicope section Melicope (Rutaceae) for the Austral Islands

Abstract Melicope balgooyi, a new species of Melicope (Rutaceae) is described. It is known only from the Austral Islands in the South Pacific (French Polynesia). However, it is not closely related to the other two species previously known from the Austral Islands, which are part of Melicope section Vitiflorae. The new species belongs to Melicope section Melicope and is most closely related to species from New Zealand, the Kermadec Islands, and the Society Islands. The new species has alternate to sub-opposite leaves, which is a very rare arrangement in Melicope and has only been described for two other species of the genus so far.


Introduction
In the course of phylogenetic and revisionary studies in Melicope J.R. Forst. & G. Forst., a new species was found, and along with its description, we discuss its biogeography and sectional placement. Melicope is the largest genus in Rutaceae, consisting of about 235 species divided into the four sections Lepta (Lour.) T.G. Hartley, Melicope, Pelea (A. Gray) Hook. f., and Vitifl orae T.G. Hartley (Hartley 2001). Molecular phylogenetic work (Appelhans et al. 2014a) supported Hartley´s (Hartley 1981, Hartley and Stone 1989, Hartley 2001) revisionary work in many ways, however, some of the taxa that were described at the genus level, namely Comptonella Baker f., Dutaillyea Baill., Picrella Baill., Platydesma H. Mann, and Sarcomelicope Engl., have been shown to belong in Melicope (Harbaugh et al. 2009, Appelhans et al. 2014a, 2014b. Also, Melicope section Melicope has been inferred as non-monophyletic (Appelhans et al. 2014a; Fig. 1). Melicope section Melicope sensu Hartley (2001) consists of 38 species with a distribution that ranges from India to the Society Islands in the South Pacifi c (Fig. 2). Th e section occurs on several Pacifi c island groups among which are the Bismarck Archipelago, the Salomon Islands, Vanuatu, Fiji, the Society Islands, Lord Howe Island, the Kermadec Islands, and New Zealand. Appelhans et al. (2014a) have found that species in section Melicope from Australia, New Guinea, and Borneo do not cluster together with the clade that contains the type species M. ternata J.R. Forst. & G. Forst. from New Zealand (Fig. 1). Instead, the species from Australia, New Guinea, and Borneo are the closest relatives of Melicope section Pelea (Appelhans et al. 2014a;Fig. 1). Th e few species from India, the Malay Peninsula, and Hainan Island (China) were not sampled by Appelhans et al. (2014a), but Hartley (2001) regarded these species as close relatives of the Bornean species. Species from the Bismarck Archipelago, the Salomon Islands, Vanuatu, and Fiji were also not sampled in the study of Appelhans et al. (2014a). Hartley (2001) regarded these species as a closely related group with affi nities to species from New Guinea. According to the phylogenetic study by Appelhans et al. (2014a) and the relationships that can be inferred from Hartley´s (2001) revisionary work, the abovementioned taxa have to be excluded from Melicope section Melicope. A monophyletic section Melicope consists only of two species from New Zealand (M. mantellii Buchanan, M. simplex A. Cunn.), one species from New Zealand and the Kermadec Islands (M. ternata), two species from Tahiti (Society Islands; M. lucida (A. Gray) A.C. Sm., M. tahitiensis Nadeaud), and the new species described here. All except one of these species were sampled by Appelhans et al. (2014a) and they formed a clade together with two specimens of an undescribed species from Rapa (Rapa Iti, Austral Islands; French Polynesia). Melicope section Melicope is thus reduced from 38 to six species (Figs 1 and 2). Th is new species of Melicope diff ers from other species in that genus by the combination of alternate to sub-opposite leaves and oblanceolate leaves with a cordate base.
Additional specimens (    Etymology. Th e species is named in honor of Dr. Max M.J. van Balgooy, a specialist of the SE Asian fl ora. Dr. van Balgooy has annotated the herbarium sheets of this new species stating that it is an "unusual Rutaceae near Platydesma". Phylogenetic studies (Harbaugh et al. 2009;Appelhans et al. 2014aAppelhans et al. , 2014b have shown that Platydesma is included within Melicope, proving Dr. van Balgooy´s assumptions to be true. In addition to M. maxii T.G. Hartley, which is endemic to Sulawesi (Indonesia), M. balgooyi is the second species of Melicope named after Dr. van Balgooy.

Characteristics of the new species and its sectional placement in Melicope
Th e new species from Rapa diff ers from most Melicope species by its alternate to sub-opposite phyllotaxis. While most Melicope species are typically opposite-leaved, some species from all sections except Vitifl orae can have whorled leaves. Th is character state is most common on the Hawaiian Islands, where eight of the 52 species (incl. four species of Platydesma; Wagner et al. 1990) can have whorled leaves with mainly three to four leaves per node (up to eight leaves per node in M. clusiifolia (A.Gray) T.G.Hartley & B.C.Stone). Only two Melicope species are reported to have sub-opposite or alternate leaves. Th e New Caledonian M. lasioneura (Baill.) Baill. ex Guillaumin usually has opposite leaves, but can have leaves in whorls of three or an alternate phyllotaxis. Melicope rubra (Lauterb. & K. Schum.) T.G. Hartley from New Guinea and northeastern Australia has opposite or rarely sub-opposite leaves. Th e alternate to sub-opposite leaves of the new taxon from Rapa therefore represent a rare condition in Melicope.
Th e placement of the new taxon in Melicope is assured by molecular phylogenetic data (Appelhans et al. 2014a), which places it close to the type M. ternata in Melicope section Melicope (Fig. 1).
Two other species of Melicope [M. bracteata (Nadeaud) S.L. Welsh and M. margaretae (F. Br.) T.G. Hartley] have been described previously from the Austral Islands, but they are both members of Melicope section Vitifl orae (Fig. 1). Among other features, the new species diff ers most distinctly from M. bracteata and M. margaretae in stamen number (8) and oblanceolate leaves with a cordate base. Melicope bracteata and M. margaretae each have 4 stamens and usually elliptic leaves with a rounded or acute base.
Th e new taxon is connected to its closest relatives within Melicope section Melicope by its 8 stamens. Morphologically, and also phylogenetically, the new taxon mostly resembles the Tahitian M. lucida and M. tahitiensis. Th e often auriculate leaf base of many specimens of M. lucida and M. tahitiensis is similar to the cordate leaf base of the new taxon. Th e leaf shape among the three taxa is also similar; however, M. lucida and M. tahitiensis have acuminate to acute apexes as opposed to a rounded or slightly obtuse apex in the new taxon. Leaves of M. lucida and M. tahitiensis are petiolate, while those of the new taxon are sessile or subsessile. Th e new species further shares unisexual fl owers and peltate stigmas with M. lucida and M. tahitiensis. Th e holotype specimen has pistillate fl owers, while the paratype has staminate fl owers, indicating the species may be dioecious like its closest relatives M. lucida and M. tahitiensis. However, it is important to note that the description of the new taxon is based on only two collections with a very low number of fl owers, so that a defi nite statement about the sexual system of the species is not possible with the data at hand.
In order to diff erentiate between Melicope and several of its closely related genera on a morphological basis, fruit and seed characters are needed (Hartley 2001, Kubitzki et al. 2011. With fruits lacking on the only known specimens of the new taxon, its position is not absolutely confi rmed from a morphological point of view. Consistent with the phylogenetic evidence, further support for the placement of the new taxon in Melicope is supported by its distribution. Out of the genera that resemble the fl owering and vegetative characters of Melicope, most taxa are distributed in Australasia and Malesia (Kubitzki et al. 2011). Only the distribution of Euodia J.R. Forst. & G. Forst. reaches deep into the Pacifi c so that one could expect to fi nd Euodia on the Austral Islands. However, the New Caledonian endemic E. tietaensis (Guillaumin) T.G. Hartley is the only Euodia species with eight stamens (like the new species) and all species that occur further eastward in the Pacifi c have four stamens (Hartley 2001).

Geology and biogeography
Th e Austral Islands are part of French Polynesia and are situated in the Southern Pacifi c. Th e Archipelago lies south of the Society Islands and consists of seven main islands of volcanic origin. Rapa is the second largest of these islands (i.e. 40 km 2 ) and is about 5 million years old. Th e island is very rugged and is characterized by its steep central ridges, mist shrouded spires, and towering black basalt sea-cliff s. Th e highest peak is Mont Perau at about 650 m (Gates Clarke 1971, Clouard and Bonneville 2005, Meyer 2010.
Th e affi nities of Rapa's fl ora are closely allied to New Zealand and Australia, yet with numerous exceptions. Th e high levels of endemic biological diversity in both the fl ora and fauna still puzzle many scientists because of the islands relatively small square area (Wood 2002). Concerning Rapa's fl oristic relationships, van Balgooy (1971) stated "I think it best to place Rapa in the SE Polynesian Province, as an anomalous district". More than 75 plant taxa are single island endemics to Rapa, including three endemic plant genera, namely Apostates N. S. Lander (Asteraceae) Pacifi geron Nesom (Asteraceae) and Metatrophis F. Br. (Urticaceae) (Wood 2002(Wood , 2010.
Th ree species of Melicope occur on the Austral Islands, which are the result of two independent colonization events. Th e newly described species is part of section Melicope and its closest relatives stem from Tahiti, the Kermadec Islands, and New Zealand. Th e two other species, M. bracteata and M. margaretae, are part of section Vitifl orae with an origin probably in the area of New Caledonia, Vanuatu, and Fiji based on the distributions of their closest relatives (Hartley 2001, Appelhans et al. 2014a. Th e new species described here is a new record within section Melicope for the Austral Islands and an updated distribution map for the newly revised section is provided in Fig. 2.

Conservation status
IUCN Red List Category. When evaluated using the World Conservation Union (IUCN) criteria for endangerment (IUCN 2001), Melicope balgooyi falls into the Critically Endangered (CR) category, which designates this species as facing the highest risk of extinction in the wild. Our evaluation can be summarized by the following IUCN hierarchical alphanumeric numbering system of criteria and subcriteria: 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 M. balgooyi include habitat degradation and destruction by feral goats (Capra hircus L.), competition with non-native plant taxa especially Psidium cattleianum Sabine, possible landslides and fi re, and the potential for inbreeding depression from small population.