Santalum austrocaledonicum var. glabrum Huerl . emend. Butaud & P.Firmenich, 2015

Butaud, Jean-Francois, 2015, Reinstatement of the Loyalty Islands Sandalwood, Santalum austrocaledonicum var. glabrum (Santalaceae), in New Caledonia, PhytoKeys 56, pp. 111-126 : 113-116

Santalum austrocaledonicum var. glabrum Huerl. emend. Butaud & P.Firmenich mut. char.

Santalum austrocaledonicum var. glabrum Hürl., Mém. Mus. Hist. Nat., ser. B, Bot. 15(1): 15 (1964).

Type.

New Caledonia, Loyalty Islands, Maré, près de Rawa, arbre, 8 m, en fleurs et en fruits, forêt mésophile, 17 July 1951, M.G. Baumann-Bodenheim 14762 (holotype: P scan!; isotype: Z scan!).

Diagnosis.

Santalum austrocaledonicum var. glabrum is most similar to var. austrocaledonicum in its glabrous inflorescence and leaves wider than 1.5 cm, which differentiates them from the other New Caledonian Santalum austrocaledonicum varieties. Santalum austrocaledonicum var. glabrum differs from Santalum austrocaledonicum var. austrocaledonicum by the seed size, which is more than 7.5 mm wide for the former and less than 7.5 mm for the latter.

Description.

Shrub to small tree 2-10 m tall, trunk up to 30 cm dbh; bark rough, grey to reddish-brown, longitudinally fissured; heartwood fragrant, yellowish to brownish. Leaves glabrous; petiole canaliculate, 7-13 mm long; blades of the mature leaves 3.5-6.0 (-6.6) × (1.6-) 2.0-3.5 (-4.1) cm, usually elliptic or rarely obovate, apex obtuse to acute or apiculate, base acute, secondary veins mostly 7-9 pairs. Inflorescences glabrous, in axillary or terminal panicles, usually trichotomous and several times branched, with 10-40 flowers; peduncles 10-38 mm long. Flowers bisexual with outer surface of petal greenish and glabrous; pedicels 1.5-2 mm long. Petals 4, narrowly triangular, 2.5-3.0 × 1.5-2.0 mm, inner surface white when opening turning brownish later; petal internal margin glabrous. Stamens 4, surrounded by long hairs at the base; the outer ones reaching the anther apex, the inner ones reflexed in the cup-shaped disk; anthers 1.5-2.7 × 0.8-1.0 mm. Disk concave, more than 2 mm deep; disk lobes fleshy and erected between petals, 1.3-1.4 × 0.8-0.9 mm. Ovary unilocular, conic, acute, 1.1-1.7 × 0.6 mm; style free, 4 mm long; stigma 3 or 4 lobed. Fruit a globose fleshy drupe, 15-21 × 12-15 mm when fresh, topped by the petal scars 3-5 mm diameter, green turning red to deep purple and black at maturity. Seed globose, with a hard endocarp (8.5-) 9.0-11.5 × 7.5-10.0 (-10.5) mm.

Phenology.

Flowering and fruiting probably occurring throughout the year but with some peaks; herbarium samples provide the following data: flowers from December to August, fruits from January to August.

Distribution.

New Caledonia, endemic to Loyalty Islands; known only from Ouvéa, Lifou and Maré islands (Figure 1 ). Not recorded on the smaller islands of Beautemps-Beaupré, Tiga and Walpole.

Habitat and biology.

This variety is restricted to the calcareous soils of uplifted atolls between 5 and 80 m elevation and is closely linked with traditional agriculture which consists of shifting cultivation. Regeneration by seeds occurs mainly in the open cultivated areas and young fallow lands. Loyalty sandalwood is therefore characteristic of fallows, shrublands and secondary forests, and rarely occurs in mature forests. It is also commonly found along roads and close to villages in open areas where it is generally protected and managed by inhabitants. The surrounding vegetation is often composed of trees and shrubs, such as Acacia spirorbis Labill., Acalypha spp., Acronychia laevis J.R.Forst. & G.Forst., Dodonaea viscosa (L.) Jacq., Elattostachys apetala (Labill.) Radlk., Glochidion billardierei Baill., Melochia odorata L.f., Morinda citrifolia L., Pandanus macrocarpus (Brongn.) Solms, Podonephelium homei (Seem.) Radlk., Polyscias bracteata (R.Vig.) Lowry subsp. bracteata ., Psidium guajava L., and Schinus terebenthifolius Raddi. Loyalty sandalwood is a hemiparasitic tree like all Santalum species; its pollination is insect-mediated whereas its fleshy fruits are dispersed mainly by doves and pigeons ( Bottin et al. 2005).

Conservation status.

Using the categories and criteria of IUCN (2001), we propose for Santalum austrocaledonicum var. glabrum the IUCN Red List Category Vulnerable (VU): B (1+2) ab (iii,v). Its population size is estimated at more than 10,000 mature individuals (excluding criteria C and D) with an extent of occurrence around 8,000 km² and an area of occupancy around 1,000 km². Criteria A can not be used due to lack of knowledge of generation length and magnitude of population size reduction. Three locations (one per island) can be distinguished without any fragmentation. A continuing decline is observed and projected in terms of habitat quality and number of mature individuals due to harvest, competition with invasive plant species ( Schinus terebenthifolius Raddi, Pluchea odorata (L.) Cass., Lantana camara L.), hybridization with other Santalum austrocaledonicum varieties used in plantations, and changes in the traditional agricultural system (less cultivated fields, short fallows...). Indeed, despite provincial regulations establishing quota and exploitability criteria, illegal logging is still occurring ( Butaud et al. 2013) whereas hybridization is suspected due to sandalwood interspecific crossability ( Tamla et al. 2012).

Common names.

The common names recorded for Santalum austrocaledonicum var. glabrum are “tapakae” (pers. obs. 2014) or “tapakai” ( Lenormand 1968) on Lifou, “wekesi” ( Lormée et al. 2011) on Maré and “wahata” ( Ozanne-Rivierre 1984) on Ouvéa.

Discussion.

Santalum austrocaledonicum var. glabrum is the sole native sandalwood in the Loyalty Islands. Nevertheless, two other varieties have been introduced for plantation purposes, mainly in Maré and Lifou: var. pilosulum from Ouen Toro in Nouméa, and var. austrocaledonicum from Isle of Pines. These plantations can be considered a risk for the Loyalty variety because of hybridization and subsequent introgression. Plantations with exotic varieties should be discouraged to preserve the Loyalty sandalwood’s morphological, genetic, sylvicultural and chemical specificities ( Bottin 2006, Bottin et al. 2007, Butaud et al. 2013, Ehrhart 1998). On the other hand, the sustainable exploitation of natural stands of Loyalty Islands sandalwood is becoming increasingly difficult with the lack of regeneration and the increasing international demand for sandalwood essential oil. Well-managed plantations with variety glabrum could be promoted to preserve the natural stands, to develop the Loyalty sandalwood sector, and to increase the production of heartwood and essential oil ( Butaud 2011, Butaud et al. 2013).

The taxonomy of Santalum austrocaledonicum still needs to be further investigated. Indeed, the study of herbarium samples of var. austrocaledonicum and previous molecular and morphometric studies ( Bottin 2006, Bouvet et al. 2005) showed significant variability. It is expected that future work supported by increased surveys and sampling of northern Grande-Terre sandalwood could reveal one or two new varieties, including one on Isle of Pines (taxon previously described as Santalum homei Seem.). Moreover, two new endemic varieties of Santalum austrocaledonicum are expected based on the recent study of Millet et al. (2012) on the genetic structure of Vanuatu sandalwood, one for the northern islands and one for the southern islands.

Figures

Figure 1. Distribution map of New Caledonian varieties of Santalum austrocaledonicum based on the specimens examined.