Nepenthes rhombicaulis is a tropical pitcher plant endemic to Sumatra. The specific epithet rhombicaulis is formed from the Latin words rhombicus, meaning "rhomboid", and caulis, "stem". It refers to the cross-sectional shape of the stem internodes. Botanical history Nepenthes rhombicaulis was first collected by Shigeo Kurata on March 29, 1972, on Mount Pangulubao at an altitude of between 1700 and 1900 m above sea level. The species was mentioned by name in a 1972 issue (volume 26, number 10, page 44) of The Heredity. It was formally described by Kurata the following year in The Gardens' Bulletin Singapore. One of the original specimens, Kurata 4300, was designated as the holotype of the species and is deposited at the herbarium of the Nippon Dental College (NDC). An isotype is held at the National Herbarium of Singapore (SING). Kurata's illustration of the type specimen shows a small apical appendage on the underside of the pitcher lid. However, Matthew Jebb and Martin Cheek pointed out that this feature is not present in the isotype held in Singapore. Kurata suggested that the appendage might be a developmental defect and of little significance. Observations made at the type locality by Charles Clarke and Ch'ien Lee seem to confirm this; while some wild plants exhibit this appendage, most do not. In the 1983 book Carnivorous Plants of the World in Colour by Katsuhiko and Masahiro Kondo, a photograph of N. gymnamphora is identified as N. rhombicaulis. In 1993, Bruce Salmon postulated that the lower pitchers of N. rhombicaulis are specially adapted to trapping subterranean insects. His observations were published in the Carnivorous Plant Newsletter. Rudolf Schmid-Höllinger reported observing upper pitchers of N. rhombicaulis on Mount Pangulubao in 1993. He published his findings the following year in the Carnivorous Plant Newsletter. Charles Clarke also reported finding one small upper pitcher in 1995. Prior to this, it was thought that the upper stem of N. rhombicaulis was only used for climbing and did not produce pitchers. However, doubts have been raised about the identity of the upper pitchers observed by Schmid-Höllinger. Description Nepenthes rhombicaulis climbs well and its stem is known to reach 35 m in length, making it one of the longest in the genus. Internodes are up to 20 cm long and 1 cm in diameter. They are usually rhomboid in cross section. The stem bears numerous sunken glands. The species has an extended rhizome which