A new species from the Fagaceae family, Castanopsis corallocarpus Tan & Strijk, is described from Royal Belum State Park in Peninsular Malaysia. Here, we provide technical illustrations, colour images and a description of its conservation status and the collecting locality, in addition to a comparative analysis with other species in the region. The solitary nut of C. corallocarpus has a morphologically unique cupule, lined with rows of thick coral-like spines not seen in other Castanopsis species.

Berangan, chinquapins, flora of Peninsular Malaysia, hill dipterocarp forest, Malayan chestnut

Castanopsis (D.Don) Spach, is the third largest genus in Fagaceae, comprising ca. 134 species (Phengklai 2008; Li et al. 2015; Strijk 2022). Apart from limestone formations, Castanopsis species can be found in various habitats, ranging from lowland rainforest to montane forest and even harsh environments, like acidic heaths and peat swamps (Soepadmo 1972). Many seem to have narrow ecological or habitat preferences though, with species often found on ridges or crests and along margins and riverbanks. All Castanopsis species are medium to large trees and, like other Fagaceae species, are co-dominant in the closed canopy layer (Soepadmo 1972). The wide geographical distribution of Castanopsis is restricted to (sub-)tropical Asia, ranging from north-eastern India (Nepal, Bhutan and Assam), parts of eastern Asia (southern China, Korea and Japan) and southeast Asia (Indochina and Malesia). The genus has two major biodiversity hotspots, namely Indochina and Malesia (Soepadmo 1972). New taxonomic discoveries of Castanopsis are skewed towards Indochina with eight new species having been described in the last few decades (Phengklai 2004; Chen et al. 2010; Chen et al. 2011; Vuong and Xie 2014; Hoang et al. 2018; Mitra et al. 2019). Interestingly, no new species of Castanopsis has been described in Malesia over the last two decades.

The dipterocarp-dominated tropical rainforests of Peninsular Malaysia are part of the megadiverse Sundaland forest range (Myers et al. 2000). It is estimated that Peninsular Malaysia has at least 9,030 vascular plant taxa comprising 248 families and 1,651 genera (Yong et al. 2021). The Fagaceae family is an important component of the rainforest in Peninsular Malaysia, with a total of 72 species comprising four genera (i.e. Castanopsis, Lithocarpus, Quercus and Trigonobalanus). Mast fruiting phenomena in the Sundaland occur on an irregular suprannual scale (2–10 years) for many plant families, resulting in long periods of crop scarcity (Medway 1972). Unlike most mast-fruiting families, tropical Fagaceae communities fruit annually at unsynchronised times throughout the year, providing an important food source for many animals during periods of low fruit availability (Kaul et al. 1986). Species in the genus are known as ‘Chinquapin’ (not to be confused with two species in the North American genus of Chrysolepis (Fagaceae), which are also often referred to as such). Locally, the genus is known as berangan in Malay or the Malayan chestnut (Corner 1988). There are 20 described Castanopsis species in Peninsular Malaysia and, of these, five species are endemic to Malaysia (Cockburn 1972; Soepadmo 1972; Strijk 2022).

Royal Belum State Park is in the State of Perak, in the north of Peninsular Malaysia. The rainforest of Belum consists of undisturbed and pristine lowland dipterocarp, hill dipterocarp and lower montane forests. Belum is part of the larger Belum-Temenggor Forest Complex (BTFC) which has an area of ca. 3,500 km². The BTFC is also part of a larger forest complex, as it shares a border with two adjacent protected areas in Thailand (Hala-Bala Wildlife Sanctuary and Bang La National Park) and forms part of the Central Forest Spine of Peninsular Malaysia. A product of the geological merger between the supercontinents of southern Gondwanaland and northern Laurasia, the landscape of BTFC is estimated to be more than 130 million years old, which is older than the Amazon and Congo Basins (Malaysian Nature Society 2005). Given its unique position within the Peninsula, the rich floristic composition of BTFC is a mixture of Thai-Burmese and Malayan flora with approximately 3000 species of flowering plants recorded, many of which are endemic to northern Peninsular Malaysia (Malaysian Nature Society 2005).

During a field expedition in Royal Belum State Park, Malaysia in July 2018, we came across a specimen with a large single nut and a unique burr that does not match any described taxa of Castanopsis. After examining the relevant literature on Malesian Fagaceae, we report this specimen as a new species, placed within the genus Castanopsis.

We report the first description of a new species, C. corallocarpus from BTFC, Perak, Malaysia. Peninsular Malaysia has a total of 20 species of Castanopsis and C. corallocarpus is easily distinguished by the unique rows of basally reinforced, blunt coral-like spines on the cupule. At least 10 species of Castanopsis species have a single nut and out of these, only two have a non-spiny cupule (i.e. Castanopsis curtisii King and Castanopsis nephelioides King ex Hook.f.). All others have either short-dense spines (Castanopsis megacarpa Gamble; Castanopsis malaccensis Gamble; Castanopsis johorensis Soepadmo; Castanopsis javanica (Blume) A.DC.; Castanopsis tungurrut (Blume) A.DC.; Castanopsis ridleyi Gamble) or thick thorns (Castanopsis rhamnifolia (Miq.) A.DC. and Castanopsis acuminatissima (Blume) A.DC.) as their main defence against seed predation.

Peninsular Malaysia and Borneo together have an estimated 103 species of Fagaceae in four genera (Castanopsis: 22; Lithocarpus: 62; Quercus: 18; Trigonobalanus: 1; Royal Botanic Gardens Kew (2021)). Numbers for the individual Bornean regions (Sabah, Sarawak, Brunei and Indonesian Kalimantan) fluctuate, depending on source and species-data considered, but it is estimated that, for the two major areas (PM and Borneo s.l.), endemism in Peninsular Malaysia is highest for Castanopsis only, whereas on Borneo, all three main genera have significant levels of endemicity (Peninsular Malaysia: C: 22%; L: 1%; Q: 0 (no endemics); Borneo s.l.: C: 46%; L: 91%; Q: 100% (all species endemic)). Many species in Lithocarpus and Quercus have ranges restricted to mid- or higher elevation habitat (> 600 m), which is more prevalent in Borneo (Soepadmo 1972), while occurrence and diversity of Castanopsis species seem to be less extremely governed by elevation, but more by the prevalence of ridges, crests, forest- and river-margins (Cockburn 1972; Soepadmo 1972).

Of the five Castanopsis species endemic to Peninsular Malaysia, four are found mostly in mid- to upland habitats, all first described from Perak (Larut and surrounding areas). A fifth endemic (C. selangorensis A.Camus) was primarily found in the lowlands, but is presumed extinct (Cockburn 1972). Castanopsis corallocarpus, a sixth endemic species of Castanopsis for Peninsular Malaysia, differs distinctly in its distribution by occurring only in the north in the lowland and hillside forest (< 450 m). Within Malaysia and the wider region, C. corallocarpus is unique in its combination of properties and we further outline some of the defining differences with other species in Table 1.

During our field survey, we encountered additional Fagaceae species, for example, Lithocarpus elegans (Blume) Hatus. ex Soepadmo, Lithocarpus wrayi (King) A.Camus, Lithocarpus cf. kingianus (Gamble) A.Camus, Lithocarpus hendersonianus A.Camus., Lithocarpus macphailii (M.R.Hend.) Barnett, Lithocarpus sundaicus (Blume) Rehder, Castanopsis inermis (Lindl.) Benth. & Hook.f., Castanopsis malaccensis and two (as of yet) unidentified species of Quercus.

Few studies have been done on Fagaceae in Peninsular Malaysia in the last decade. The discovery of C. corallocarpus in Peninsular Malaysia highlights the continued potential of new findings for this family in the region. Moreover, with only two recorded individuals of C. corallocarpus in BTFC, further assessment is needed to determine the extent of the species distribution for its conservation. This also extends to other Fagaceae species from Castanopsis and Lithocarpus in which many are data-defficient on the IUCN Red List (IUCN 2022).

This discovery was part of fieldwork conducted under LO’s Ph.D. that was funded by Yayasan Sime Darby (grant M0005.54.04) and the University of Nottingham Malaysia and subsequent work by the Southeast Asia Biodiversity Research Institute (SEABRI; grant #Y4ZK111B01). We are grateful to the Perak State Park Corporation for allowing us to carry out the collection and Tang Fook Leong from RIMAU for accommodating us in Sungai Papan. We are especially grateful to the Orang Asli field staff, Param bin Pura, Muhamad Tauhid bin Tunil and Sudin bin Tunil for their assistance when sampling. We are grateful to Forest Research Institute Malaysia for housing the Type specimen. We would also like to thank the subject editor Dr. Norbert Holstein and the two reviewers for their constructive comments.