Vatica pentandra (Dipterocarpaceae) is an endemic tree found only in Kutai Kartanegara Regency, East Kalimantan Province, Indonesia. The species is categorized as Critically Endangered on the IUCN Red List using criteria A1c, C2a, D, which focus on population size and reduction (P. Ashton, 1998, dx.doi.org/10.2305/IUCN.UK.1998.RLTS.T33455A9785565.en). The tree is known from only a single collection, made in 1955 along the Belayan River near Tabang District (P. Ashton, 1978, Gardens’ Bulletin, Singapore, XXXI, 5–48). There has been no further record of this tree, and it is not known to be present in any ex situ conservation collections (BGCI, 2020, PlantSearch database).

To provide information for an updated assessment of this threatened species, we conducted a survey in February 2020 in a total of 14 localities along the Belayan River, within the villages of Sungai Lunuk, Umaq Dian and Gunung Sari in Tabang District and Long Beleh Village in Kembang Janggut District. We tried to survey as wide a range of habitats as possible: from hilly, upstream areas of Sungai Lunuk Village to flat, downstream areas of Long Beleh Village. The elevation range of the surveyed areas was 12–123 m. Despite these searches, which included the likely type locality described on herbarium specimens, we did not locate V. pentandra.

We believe that extensive loss of forests, to oil palm plantations and coal mining, is the most likely reason for our failure to relocate V. pentandra. In addition, forestry companies are extracting timber from forests along the Belayan River. With these forests greatly reduced and fragmented, the areas we surveyed are some of the last remaining forested areas along this river.

Although we recommend further surveys for V. pentandra, especially in upstream areas of Belayan River, in the northern Tabang Regency where forests are still in relatively good condition, we are able to update the conservation assessment of this species. Based on the findings of our survey, we reassess V. pentandra as Critically Endangered based on criteria A2cd; i.e. with more than 80% suspected population reduction in the last three generations (A2) based on a decline in area of occupancy, extent of occurrence and/or habitat quality (c), and potential level of exploitation (d). The forests of Kalimantan continue to be affected by conversion and degradation, and our updated assessment of this endemic tree species is an urgent call for the conservation of this and the other species of these forests.