[4] The first known collection of N. thorelii was made by Clovis Thorel between 1862 and 1866[5] from Ti-tinh, Lo-thieu, Guia-Toan, Vietnam.

It is deposited at the Museum National d'Histoire Naturelle in Paris, together with one isotype: a female specimen with upper pitchers.

[8] 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.

[9] 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.

[6] The authors noted that there are "problems with the delimitation" of N. thorelii and the related taxa N. anamensis and N. smilesii[6] (which are now considered conspecific).

[12] 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.

[13] A plant identified as N. thorelii was also used as part of a 2012 study into the sterility and antimicrobial properties of pitcher fluid.

[14] In November 2009, photographs surfaced on the internet which appeared to show N. thorelii in its natural habitat in Vietnam, growing at 0–200 m above sea level.

[15] In February 2010, Charles Clarke and François Mey travelled to the site where the photographs had been taken, as well as to the type location, but were unable to find any remaining plants of this species.

The so-called Sữa Đá population was found by a team including François Mey, Alastair Robinson and Luu Hong Truong, curator of the VNM Herbarium in Ho Chi Minh City, and was estimated to number fewer than 100 individuals.

[17] The discovery was announced online by Alastair Robinson on August 6, 2011:[17] As of today, Nepenthes thorelii has officially been relocated in Vietnam, within Tay Ninh province, its type locality [...] the specimens studied in situ at the so-called Sữa Đá (Sua Da) site fall neatly into the description made by Lecomte in 1909, and match the specimens at the Paris herbarium perfectly.

Given the recent elimination of potential communities of this taxon by poachers, details of the site will not be made public for the foreseeable future, a decision made in concert with the Institute of Tropical Biology in Ho Chi Minh -- with whom we conducted the expedition -- in order to protect this critically endangered taxon.Nepenthes thorelii is a shrub with an erect stem having a smooth circular cross section and a tapering form.

Numerous prominently lipped glands are present on the underside of the lid, particularly near the base of the midrib, where they are 0.3 to 0.7 mm wide.

[24] In comparison, N. thorelii has an amplexicaul leaf attachment and the base of the lamina is decurrent into two wings that extend up to 2.5 cm down the stem.

[6] In addition, N. thorelii has wholly ovoid lower pitchers, whereas those of N. bokorensis are only ovate in the basal third, becoming cylindrical above.

[24] In his Carnivorous Plant Database, taxonomist Jan Schlauer treats N. suratensis as a possible heterotypic synonym of N. thorelii.