The first known collection of N. thorelii was made by Clovis Thorel between 1862 and 1866 from Ti-tinh, Lo-thieu, Guia-Toan, Vietnam.
During this time, Thorel collected a number of specimens of N. thorelii, all of which have been designated as Thorel 1032.
One of these specimens, the lectotype, is a male plant with lower pitchers.
It is deposited at the Museum National d'Histoire Naturelle in Paris, together with one isotype: a female specimen with upper pitchers.
A second isotype is held at Herbarium Bogoriense (BO), the herbarium of the Bogor Botanical Gardens.
An additional specimen of Thorel 1032 is deposited at the New York Botanical Garden.

Nepenthes thorelii was formally described in 1909 by French botanist Paul Henri Lecomte, who named it after Thorel.
The description was published in Lecomte's Notulae systematicae.
Since then, one infraspecific taxon of N. thorelii has appeared in print; Nepenthes thorelii f. rubra was mentioned by Leo C. Song in a 1979 article published in the Carnivorous Plant Newsletter, but is considered a nomen nudum.

In 1983, Bruce Lee Bednar wrote that cultivated plants labelled as N. kampotiana were thought to represent a natural hybrid between N. mirabilis and N. thorelii, and that these appeared on some lists under the unofficial name N. × lecouflei.
Bednar noted that a plant known in the horticultural trade as "thorelii-long green" was considered by many to be a Thailand form of N. mirabilis, while another plant called "short round", which had pubescent leaves and squat pitchers, might represent the true N. thorelii.
If this were the case, it would mean that artificial crosses such as N. 'Hachijo' and N. 'Effulgent Koto' are intergrades of N. mirabilis as opposed to hybrids.

In their 1997 monograph on the genus Nepenthes, Matthew Jebb and Martin Cheek designated the male specimen deposited at the Paris herbarium as the lectotype of N. thorelii.
The authors noted that there are "problems with the delimitation" of N. thorelii and the related taxa N. anamensis and N. smilesii (which are now considered conspecific).

Compounds derived from plants identified as N. thorelii have been the subject of some research.
A 1998 article reported that naphthoquinones originating from N. thorelii showed antimalarial activity.
This was followed by a paper in 2007 that studied the isozymic composition of nepenthesin in the pitcher fluid of a number of species, including one referred to N. thorelii.
A plant identified as N. thorelii was also used as part of a 2012 study into the sterility and antimicrobial properties of pitcher fluid.
The first known collection of N. thorelii was made by Clovis Thorel between 1862 and 1866 from Ti-tinh, Lo-thieu, Guia-Toan, Vietnam. During this time, Thorel collected a number of specimens of N. thorelii, all of which have been designated as Thorel 1032. One of these specimens, the lectotype, is a male plant with lower pitchers. It is deposited at the Museum National d'Histoire Naturelle in Paris, together with one isotype: a female specimen with upper pitchers. A second isotype is held at Herbarium Bogoriense (BO), the herbarium of the Bogor Botanical Gardens. An additional specimen of Thorel 1032 is deposited at the New York Botanical Garden.
Nepenthes thorelii was formally described in 1909 by French botanist Paul Henri Lecomte, who named it after Thorel. The description was published in Lecomte's Notulae systematicae. Since then, one infraspecific taxon of N. thorelii has appeared in print; Nepenthes thorelii f. rubra was mentioned by Leo C. Song in a 1979 article published in the Carnivorous Plant Newsletter, but is considered a nomen nudum.
In 1983, Bruce Lee Bednar wrote that cultivated plants labelled as N. kampotiana were thought to represent a natural hybrid between N. mirabilis and N. thorelii, and that these appeared on some lists under the unofficial name N. × lecouflei. Bednar noted that a plant known in the horticultural trade as "thorelii-long green" was considered by many to be a Thailand form of N. mirabilis, while another plant called "short round", which had pubescent leaves and squat pitchers, might represent the true N. thorelii. If this were the case, it would mean that artificial crosses such as N. 'Hachijo' and N. 'Effulgent Koto' are intergrades of N. mirabilis as opposed to hybrids.
In their 1997 monograph on the genus Nepenthes, Matthew Jebb and Martin Cheek designated the male specimen deposited at the Paris herbarium as the lectotype of N. thorelii. The authors noted that there are "problems with the delimitation" of N. thorelii and the related taxa N. anamensis and N. smilesii (which are now considered conspecific).
Compounds derived from plants identified as N. thorelii have been the subject of some research. A 1998 article reported that naphthoquinones originating from N. thorelii showed antimalarial activity. This was followed by a paper in 2007 that studied the isozymic composition of nepenthesin in the pitcher fluid of a number of species, including one referred to N. thorelii. A plant identified as N. thorelii was also used as part of a 2012 study into the sterility and antimicrobial properties of pitcher fluid.
Nepenthes thorelii