Acriopsis ridleyi Hook.f. (Orchidaceae): Re-encounter of an orchid thought extinct since its 1889 holotype collection in Singapore

This paper reports the rediscovery of a Presumed Nationally Extinct species, Acriopsis ridleyi. The only other previous collection of this orchid in Singapore was the holotype, collected at ‘Bukit Mandi’ (Bukit Mandai) by J. S. Goodenough (one of H. N. Ridley’s collectors of forest trees) in 1889. It was presumed to be locally extinct as there were no further collections until 2017, when a clump was found growing on a branch some 18 m up a Dillenia grandifolia tree growing on a steep slope in Bukit Timah Nature Reserve. A portion of this was collected for propagation and future reintroduction. This species is thus documented as a re-discovery and classified as nationally Critically Endangered owing to its rarity in Singapore.