Nusakambangan is a small island of 210 km² on the southern coast of Cilacap Regency, Central Java Province, Indonesia, with high flora diversity and various types of forests from mangrove to limestone hill forests. There are > 750 plant species known from the island, including two endemic species Lagerstroemia vanosii W.J.de Wilde & Duyfjes (Lythraceae) and Piper mucronulatum Blume (Piperaceae). Lagerstroemia vanosii is a tree species known only from herbarium specimens, last collected by Koorders on 4 March 1902. Piper mucronulatum is a woody climber known from a single herbarium specimen collected before 1826. To our knowledge, these two endemic plants have not been observed for more than a century, are not known to be present in any ex situ conservation areas, and their conservation status has not been assessed.

In January 2022, we surveyed the only two protected areas in Nusakambangan Island, West and East Nusakambangan Nature Reserves, and one unprotected area between the Reserves. We attempted to survey a wide range of vegetation types, including mangrove, coastal, lowland and limestone hill forests across altitudes of 0–190 m. Despite intensive searches, we were unable to locate either species.

Habitat conversion and invasive plants are potentially the two main threats to these endemic species and the most likely reasons for our failure to relocate them. Many forested areas on the island have been converted into settlements, agriculture fields and limestone mines. The invasive palm, langkap Arenga obtusifolia Mart., is a serious threat to the island ecosystem in general. Once it dominates a forest stand, other plants struggle to survive because of both vertical and horizontal constraints related to canopy shade, roots and competition.

We recommend that both endemic species should be categorized as Critically Endangered on the IUCN Red List under criteria A2c; i.e. a population decline of > 80% in the last three generations (A2) based on a decline in area of occupancy, extent of occurrence, and habitat quality (c). We recommend additional surveys for these two species in other locations on Nusakambangan. Conservation interventions are required to halt the ongoing conversion of forest and the domination of the invasive palm.