"Over het geslacht Nepenthes" is a monograph

Monograph

A monograph is a work of writing upon a single subject, usually by a single author.It is often a scholarly essay or learned treatise, and may be released in the manner of a book or journal article. It is by definition a single document that forms a complete text in itself...

 by Pieter Willem Korthals

Pieter Willem Korthals

Pieter Willem Korthals was a Dutch botanist. Korthals was the official botanist with the Dutch East India Service from 1831 to 1836....

 on the tropical pitcher plant

Pitcher plant

Pitcher plants are carnivorous plants whose prey-trapping mechanism features a deep cavity filled with liquid known as a pitfall trap. It has been widely assumed that the various sorts of pitfall trap evolved from rolled leaves, with selection pressure favouring more deeply cupped leaves over...

s of the genus Nepenthes

Nepenthes

The Nepenthes , popularly known as tropical pitcher plants or monkey cups, are a genus of carnivorous plants in the monotypic family Nepenthaceae. The genus comprises roughly 130 species, numerous natural and many cultivated hybrids...

. It was published in 1839 in Coenraad Jacob Temminck

Coenraad Jacob Temminck

Coenraad Jacob Temminck was a Dutch aristocrat and zoologist.Temminck was the first director of the National Natural History Museum at Leiden from 1820 until his death. His Manuel d'ornithologie, ou Tableau systematique des oiseaux qui se trouvent en Europe was the standard work on European birds...

's Verhandelingen over de Natuurlijke Geschiedenis der Nederlandsche overzeesche bezittingen. It is generally regarded as the first monograph on Nepenthes.

Korthals recognised 9 species: N. ampullaria

Nepenthes ampullaria

Nepenthes ampullaria , the Flask-Shaped Pitcher-Plant, is a very distinctive and widespread species of Nepenthes, present in Borneo, Sumatra, Thailand, Peninsular Malaysia, Singapore, the Maluku Islands, and New Guinea...

, N. bongso

Nepenthes bongso

Nepenthes bongso is a tropical pitcher plant endemic to Sumatra, where it has an altitudinal distribution of 1000–2700 m above sea level. The specific epithet bongso refers to the Indonesian legend of Putri Bungsu , the spirit guardian of Mount Marapi.The species was formally described by Pieter...

, N. boschiana

Nepenthes boschiana

Nepenthes boschiana , or Bosch's Pitcher-Plant, is a tropical pitcher plant endemic to Borneo. It is most closely related to N. faizaliana. Nepenthes borneensis is considered a synonym of this species. Nepenthes boschiana has no known natural hybrids...

, N. distillatoria

Nepenthes distillatoria

Nepenthes distillatoria is a tropical pitcher plant endemic to Sri Lanka. It was the second Nepenthes species to be described in print and the first to be formally named under the Linnaean system of taxonomy...

, N. gracilis

Nepenthes gracilis

Nepenthes gracilis , or the Slender Pitcher-Plant, is a very 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...

, N. gymnamphora

Nepenthes gymnamphora

Nepenthes gymnamphora is a tropical pitcher plant native to the Indonesian islands of Java and Sumatra. There is much debate surrounding the taxonomic status of this species and the taxa N. pectinata and N. xiphioides....

, N. madagascariensis

Nepenthes madagascariensis

Nepenthes madagascariensis is one of two Nepenthes pitcher plant species native to Madagascar, the other being N. masoalensis.-Botanical history:...

, N. phyllamphora (now known as N. mirabilis

Nepenthes mirabilis

Nepenthes mirabilis , or the Common Swamp Pitcher-Plant, is a tropical carnivorous plant species of the pitfall trap variety. It has by far the widest distribution of any Nepenthes species and is known from the following countries and regions: Borneo, Sumatra, Thailand, Peninsular Malaysia,...

), and N. rafflesiana

Nepenthes rafflesiana

Nepenthes rafflesiana , or Raffles' Pitcher-Plant, is a species of pitcher plant. It has a very wide distribution covering Borneo, Sumatra, Peninsular Malaysia, and Singapore. Nepenthes rafflesiana is extremely variable with numerous forms and varieties described. In Borneo alone, there are at...

. Three of these—N. bongso, N. boschiana, and N. gracilis—were described for the first time, and six were illustrated with watercolour paintings.