Vatica najibiana Ummul-Nazrah (Dipterocarpaceae), from the Relai Forest Reserve, Gua Musang, Kelantan and Gua Tanggang, Merapoh, Pahang, is described and illustrated. This species is Endangered and known from small populations restricted to two isolated karst limestone hills. The type locality, Relai Forest Reserve limestone, is currently under threat from encroaching oil palm plantations and ongoing logging, which, if it continues, will threaten the Kelantan population with extinction. The morphology of V. najibiana and the similar V. odorata subsp. odorata and V. harmandiana is compared.

Dipterocarpaceae , Vatica , Kelantan, Pahang, limestone hills, oil palm, logging

In Peninsular Malaysia, Vatica L., known in Malay as resak, includes 32 species (Saw 2002; Ashton and Appanah 2004; El-Taguri and Latiff 2010, 2012; Tan et al. 2014; Chua et al. 2015). It is a genus of understorey and main canopy trees from lowland forest to hill dipterocarp forest but it also occurs in coastal peat swamp and other swampy areas with only V. harmandiana Pierre and V. kanthanensis Saw restricted to limestone habitats. In Ashton and Appanah (2004) and Chua et al. (2015), V. harmandiana was called V. cinerea King that Pooma et al. (2017, p. 670) argued was a synonym of V. harmandiana. The genus Vatica is distinctly different from other Malayan genera of Dipterocarpaceae. Most Vatica species are small or medium-sized trees, unbuttressed with smooth bark and leaves with reticulate tertiary venation. There are two sections in Vatica: sect. Vatica with equal fruit calyx lobes and sect. Sunaptea with unequal fruit calyx lobes. This new Vatica species belongs to sect. Sunaptea, which now includes ten species.

This new Vatica species was discovered on the summit of a karst limestone hill within the Relai Forest Reserve, Gua Musang District, Kelantan, during the biodiversity survey of the flora of five sizeable limestone hills scattered within the FELDA Chiku oil palm plantation (Kiew et al. in prep.). The impetus for the survey was the issuing of a licence to quarry the largest hills named FELDA Chiku 7 and FELDA Chiku 8 to supply limestone to a new cement factory reputed to be the largest in SE Asia (Utusan Online 2015). The aim of the survey was to document the flora of the two hills scheduled for quarrying, which were previously hardly known botanically and to test the assertion by the cement company that protecting another nearby hill, FELDA Chiku 4, would compensate for biodiversity lost from the two larger hills. None of the limestone hills within the FELDA Chiku plantation is legally protected and all are currently under threat from disturbance associated with the oil palm plantation (clearing and burning the limestone forest around the base of the hills, grazing by free ranging cattle, hunting of the protected serow, Capricornis sumatraensis, collecting orchids etc.). Due to these threats, one species, Impatiens chikuensis, that is a strict endemic known only from FELDA Chiku 5 and 8, faces extinction (Kiew 2016).

The limestone hill flora in Peninsular Malaysia is being exploited and disturbed by quarrying, clearing the surrounding forest for agricultural plantations or burning limestone vegetation during land clearing, disturbance associated with caves, the establishment of temples and resorts, as well as from recreational and tourism activities (Kiew 1997). Kiew et al. 2017 demonstrated that no single hill has more than a fraction of limestone flora and that 192 species are endangered being known from less than five localities limestone hills, for example Monophyllaea musangensis A. Weber (Weber 1998), Gymnostachyum kanthanense Kiew, Meiogyne kanthanensis Ummul-Nazrah & J.P.C.Tan and Vatica kanthanensis Saw (Tan et al. 2014), Impatiens glaricola Kiew and Impatiens vinosa Kiew (Kiew 2016). Therefore, limestone hills are one of the most threatened vegetation types in Peninsular Malaysia and are recognised nationally as Environmentally Sensitive Areas because of their high biodiversity and vulnerability (73 of the 445 hills are the sites of active or former quarries, Liew et al. 2016). In addition, many karsts are still incompletely known botanically meaning that new species await discovery. For example, during the botanical survey of the Chiku limestone (Kiew et al. in prep.), several rare and endangered species were discovered, including this new species.

In determining the identity of the specimens, we discovered that the species had in fact already been collected from Gua Tanggang (a.k.a. Tagang) in Merapoh, Pahang, a limestone hill about 40 km south of the Relai Forest Reserve limestone but that it had been incorrectly identified as Vatica cinerea King (now V. harmandiana), a species restricted to NW Malaysia (Chua et al. 2010).

The new Vatica species was discovered on a limestone hill (5.024478 N, 102.114360 E, Ktn 50, numbering follows Price 2014) in the Relai Forest Reserve (Ktn 50), Gua Musang District, Kelantan. Herbarium specimens were collected and a photographic record was made. The population was in mature fruit but a few old dried flowers were obtained. The extensive collection of Dipterocarpaceae in the Kepong Herbarium (KEP) was used for comparison and for measurements of similar species and the other specimen of this new taxon (FRI 44774), previously collected from Gua Tanggang (a.k.a. Tagang), Merapoh, Pahang was examined in detail. The description of the new species was compared with similar species in standard texts (Saw 2002; Ashton and Appanah 2004; El-Taguri and Latiff 2010, 2012; Tan et al. 2014; Chua et al. 2015). The description is based on field observations and comparison by using KEP herbarium specimens. The provisional conservation assessment is based on the IUCN Red List Categories and Criteria Version 3.1 (IUCN 2012).

We wish to express our gratitude for the support and encouragement given by the Director-General of Forest Research Institute Malaysia (FRIM). The research was carried out as part of the Flora of Peninsular Malaysia Project at the Forest Research Institute Malaysia, funded by the Ministry of Natural Resources and Environment (NRE) of Malaysia under the 11^th Malaysian Plan (SPPII No. P23085100018003); and “Towards conservation strategy/policy for limestone hills in Peninsular Malaysia: Understanding and documenting plant biodiversity focus on Kelantan and Perlis limestone hill (Phase 1)” under National Conservation Trust Fund for Natural Resources (NCTF). The authors thank Dr L.G. Saw and Dr R.C.K. Chung for their support and comments on the manuscript; the KEP field and herbarium team for their invaluable support, the local resident guide in FELDA and to N. Mohamad-Aidil for the botanical illustration. We would also like to thank the editor and two reviewers, Dr P.S. Ashton and Dr M.R. Cheek for their useful comments on the paper.