Nepenthes eustachya is a tropical pitcher plant endemic to Sumatra, where it grows from sea level to an elevation of 1600 m. The specific epithet eustachya, formed from the Greek words eu (true) and stachys (spike), refers to the racemose structure of the inflorescence. Botanical history Nepenthes eustachya was probably first collected in February 1856 by Johannes Elias Teijsmann on the Sumatran coast near the port town of Sibolga. This specimen, Teijsmann 529, was designated as the lectotype of N. eustachya by Matthew Jebb and Martin Cheek in their 1997 monograph. It is deposited at the herbarium of the Bogor Botanical Gardens along with two isotypes. Nepenthes eustachya was described in 1858 by Friedrich Miquel. In 1908, John Muirhead Macfarlane retained N. eustachya as a distinct species in his revision of the genus, titled "Nepenthaceae". B. H. Danser did not support this interpretation and instead treated N. eustachya in synonymy with N. alata in his seminal monograph, "The Nepenthaceae of the Netherlands Indies", published in 1928. He wrote: N. eustachya Miq., only recorded from Sumatra and still distinguished by Macfarlane, is united with N. alata in the above. In his monograph, Macfarlane places N. alata in the group with carinate lid, N. eustachya among the species without keel on the lid ; yet he distinguishes a N. alata var. ecristata, without keel. For the rest there is hardly any difference to be stated between these two species and especially the inflorescences are strikingly alike. Danser also identified Ridley 16097 from the Malay Peninsula as N. alata, extending the species's range even further and making its apparent absence from Borneo difficult to explain. Ridley 16097 is now thought to represent a mixed collection of N. alba and N. benstonei. Plants belonging to N. eustachya were identified as N. alata by a number of subsequent authors, including Shigeo Kurata in 1973, Mitsuru Hotta and Rusjdi Tamin in 1986, Mike Hopkins, Ricky Maulder and Bruce Salmon in 1990, and T. Sota, M. Mogi and K. Kato in 1998. In 1997, N. eustachya was once again elevated to species rank by Matthew Jebb and Martin Cheek, who noted a number of differences between the two taxa. Charles Clarke supported this interpretation in his 2001 monograph, Nepenthes of Sumatra and Peninsular Malaysia. The specific epithet eustachya has been misspelled several times in the literature, including once by Otto Stapf in 1886 as N. eustachys and