Novitates neocaledonicae III: A new species of Citronella (Cardiopteridaceae) endemic to New Caledonia

A new species of Cardiopteridaceae, Citronella hirsuta, endemic to the east-central part of New Caledonia’s main island, Grande Terre , distinguished on the basis of morphological evidence, is described and illustrated. This new species is distinguished by its densely hirsute leaves, while the two others species of Citronella occurring in New Caledonia have glabrous leaves. Citronella hirsuta is restricted to ultramafic substrate, and only known from areas that are situated within mining concessions. A preliminarily IUCN conservation status of Endangered (EN) is proposed.


Introduction
Icacinaceae were treated in the Flore de la Nouvelle-Calédonie et Dépendances by Villiers (1980), with a total of three genera and four species recognized. More recently the family has been shown to be polyphyletic (Kårehed 2001;Stull et al. 2015) and as a consequence all the New Caledonian representatives were assigned to different families. Firstly, Apodytes E.Mey ex Arn. (1841: 155), a genus of ~15 species of the Old World tropics, ranging from Africa to Queensland (Mabberley 2008), was recently placed in Metteniusaceae, and is represented by a single species in New Caledonia, A. clusiifolia (Baill.) Villiers (1980: 160). Secondly, Gastrolepis Tiegh. (1897: 115), endemic to New Caledonia, is now placed in Stemonuraceae, where it comprises two species, G. austrocaledonica (Baill.) R.A. Howard. (1940: 481) and G. alticola Munzinger, McPherson & Lowry (2008: 776). Finally, Citronella D. Don (1832: 243) belongs to Cardiopteridaceae and has two species in New Caledonia, viz. C. macrocarpa Hürl. (in Guillaumin 1964: 60) and C. sarmentosa (Baill.) R.A. Howard (1940: 475). Mabberley (2008) indicates that Citronella has a total of twenty-one species and is distributed from Malesia across the Pacific to tropical America, and that its members exhibit the Nozeran architectural model of (Hallé et al. 1978), which is uncommon.
Although Citronella is said to have glabrous leaves and petioles in New Caledonia according to the Flore (Villiers 1980), material with a distinct indument on the leaves and petioles was collected for the first time in 2004, suggesting that it represented an entity that was not seen by Villiers. Additional collections and morphological studies conducted over the last decade have clearly confirmed that this material represents a distinct entity. As well, all known Pacific species of Citronella are trees, except C. sarmentosa (Howard 1942); thus this shrubby taxon cannot be confused with any species outside the archipelago and is therefore considered as a new species, which we describe and illustrate here. An identification key of Citronella in New Caledonia is provided, and a preliminary IUCN status is proposed.

Materials and Methods
All material of Citronella with an indument on the leaves and petioles was received on loan from NOU and P, and was studied at MPU (herbarium acronyms follow Thiers 2015). It was compared with 13 specimens of C. macrocarpa and 40 specimens of C. sarmentosa from P and MPU, as well as with information presented in key publications dealing with the taxonomy of the genus (Howard 1940;Howard 1942;Villiers 1980;Smith 1985). Measurements and shapes of various features are based on the examination of herbarium material, while colours were observed in the field by the first author. For the preparation of the description provided below, material was examined using a Leica S6D binocular microscope and photos were taken in the field with a Nikon D70 camera mounted with a 60 mm macro lens. The risk of extinction assessment was conducted using the IUCN Red List criteria (IUCN 2012); AOO value was calculated by using the online "geocat" software "http://geocat.kew.org" (Bachman et al. 2011).

Taxonomy
Key to the species of Citronella in New Caledonia 1.
Leaves and petioles with dense orange/golden hirsute indument; inflorescence densely hirsute with orange/golden trichomes ~0.5 mm in length (Fig. 1A)   Note:-Three sheets in P (P04468794, P04468795 & P04468796) that clearly belong to Citronella sarmentosa bear labels for MacKee 12882 indicating a tree 15 m tall. However, the specimen at NOU (NOU050651) of this same number is a species of Cunoniaceae, Geissois polyphylla Lécard ex Guillaumin (Guillaumin 1940: 244), as confirmed by Hopkins et al. (2014), and examination of MacKee's fieldbook reveals that the specimens at P were wrongly labeled and in fact correspond to MacKee 12881 (originally identified as "Sarcanthidion Baill."=Citronella), which is a 3 m tall shrub, corresponding to the habit of C. sarmentosa. Note:-Lasianthera austrocaledonica Baill. (1873-1876: 193) was designated as the type species in the description of the genus Gastrolepis Tiegh. (1897: 116), but van Tieghem only implied the new combination and didn't clearly associated the final epithet with the new generic name; thus the combination is not valid following art. 35.2 (McNeill et al. 2012), and the correct citation is Gastrolepis austrocaledonica (Baill.) R.A. Howard (1940: 481). Diagnosis:-The new species resembles Citronella sarmentosa in lacking domatia on the abaxial surface of its leaves, in forming small shrubs, and in having terminal, erect inflorescences, but can be distinguished by the dense, persistent hirsute indument on its leaves, petioles and inflorescences axes, versus glabrous leaves and petioles, and short, appressed trichomes on the inflorescences axes in C. sarmentosa.
Phenology:-Flowers of Citronella hirsuta have been observed in December and February, and immature fruits have been collected in April.
Distribution and Ecology:-This new species is only known from the east-central part of New Caledonia's main island, Grande Terre, in North Province (Fig. 3), where it occurs in thalweg (gully) forest and dense maquis vegetation on ultramafic substrate, at around 200 meters elevation. Only five adult individuals are known but intensive field prospection in the area could potentially locate other individuals.
Etymology:-The plant is named based on the unique nature of its indumentum among New Caledonian Citronella species.
Species recognition:-Even sterile, individuals of Citronella hirsuta can easily be distinguished from its New Caledonian congeners by its unique hirsute indument of orange/golden trichomes found on the leaves, including both the petiole and blade, as well as the inflorescence. Citronella hirsuta also differs from C. macrocarpa by lacking domatia on the abaxial surface of its leaves, and the fact that it is a small shrub, rather than always having at least one domatium in the axil of a secondary vein where it joins the midvein (and sometime also between secondary and tertiary veins), and in being a large tree up to 40 cm in diameter that has been exploited for its wood (in Sarlin 1954, confused with C. sarmentosa at that time; C. macrocarpa was published 10 years later). All three New Caledonian species of Citronella have indument on their inflorescences but in C. sarmentosa and C. macrocarpa the trichomes are scattered and appressed (Fig. 1B, C), whereas in C. hirsuta they are numerous and erect (Fig. 1A). Moreover, C. sarmentosa and C. hirsuta have erect, terminal inflorescences (in addition to accessory axillary inflorescences) with orange/golden trichomes, whereas C. macrocarpa has long, pendant, ramiflorous inflorescence with white/grey trichomes. The petiole of C. hirsuta also differs in generally not exceeding 1 cm long, whereas C. sarmentosa and C. macrocarpa have a petiole that measures 1-2 cm long. The subglobose to ellipsoid ovary with its very short style distinguishes C. macrocarpa from C. hirsuta and C. sarmentosa, which have an ovary and style forming a slender structure whose parts are difficult to distinguish. Two stigmas can be distinguished on the styles of C. hirsuta and C. macrocarpa, whereas there is only a single stigma in C. sarmentosa. Conservation status:-The plant is only known from 2 subpopulations, both located within mining concessions (Fig. 3) belonging to two different mining companies. Thus, the two subpopulations are considered as two distinct locations (sensu IUCN). The AOO calculated is 27 km². In the case of the Bota Mere specimen, the area was the focus of a botanical inventory for possible future mining activities. Citronella hirsuta is assigned a preliminary conservation status of Endangered (EN B2 a,b(iii)) using the IUCN Red List criteria (IUCN 2012).