Nepenthes Gracilis

Nepenthes gracilis ( /nɨˈpɛnθiːz ˈɡræsɨlɪs/; from Latin: gracilis "slender"), or the Slender Pitcher-Plant, is a common lowland pitcher plant that is widespread in the Sunda region. It has been recorded from Borneo, Peninsular Malaysia, Singapore, central Sulawesi, Sumatra, and southernmost Thailand. The species has a wide altitudinal distribution of 0 to 1100 m (and perhaps even 1700 m) above sea level, although most populations are found below 100 m and plants are rare above 1000 m. Despite being a widespread plant, natural hybrids between N. gracilis and other species are quite rare.

The small, elongated pitchers of N. gracilis appear relatively unremarkable and have a very thin peristome. Nevertheless, the species is unusual (and possibly unique) in that the underside of the pitcher lid bears an uneven layer of wax crystals. This layer is not as thick as, and structurally distinct from, that found in the waxy zone of the pitcher interior, and insects can easily adhere to it in dry conditions. During downpours, however, it functions as part of a trapping mechanism, whereby the impact of raindrops striking the lid causes insects to lose their footing and fall into the pitcher cup below.

Nepenthes gracilis was formally described by Pieter Willem Korthals in his 1839 monograph, "Over het geslacht Nepenthes".

Left: Nepenthes gracilis upper pitcher with a Polyrhachis pruinosa ant (A and B), showing the waxy zones of the pitcher interior and lower lid surface.

Centre: Scanning electron micrographs revealing the ultrastructure of N. gracilis wax crystals on the inner surface of the pitcher (A and B) and underside of the lid (C and D).
Right: Prey capture efficiency of the two waxy layers and peristome of N. gracilis under 'dry', 'raining' and 'wet' conditions.

Trapping function of N. gracilis pitcher lid under experimental conditions

Ants being flicked off the waxy lower surface of the lid by the action of simulated rain The same experiment carried out with an isolated lid held in place with a paper clip High-speed recording showing a house fly (Musca domestica) falling into a pitcher following raindrop impact (recording frame rate: 428 s−1, playback frame rate: 10 s−1)