Nepenthes thorelii

Species of pitcher plant from Indochina

Nepenthes thorelii /n//ᵻ/'/p//ɛ//n//θ//iː//z// //θ//ɒ/'/r//ɛ//l//i//aɪ/ is a tropical pitcher plant endemic to Indochina. Very little is known about N. thorelii and it is unlikely to have entered cultivation, although various other taxa are often mislabelled as this species in the plant trade. Prior to its rediscovery in 2011, N. thorelii was considered possibly extinct, both in the wild and in cultivation.

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. 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. 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.

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. 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. Nepenthes thorelii was rediscovered within a military zone in Tây Ninh Province, Vietnam, in August 2011. 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. 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. This is therefore the first time that the species has been formally identified and collected [ ] by qualified botanists in one hundred and two years. 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. The stem reaches 40 cm in height and is 4 to 8 mm in diameter. The species has a well developed perennial rootstock that produces shoots every wet season. The rootstock is irregularly branched and measures up to 2 cm in width. However, a 1997 study by Günther Rudolf Heubl and Andreas Wistuba found the chromosome number to be 80, and this is now accepted as the diploid number of all species in the genus.

Nepenthes thorelii is known with certainty only from Vietnam, where the type specimen was collected. Nepenthes thorelii occurs in seasonally dry savannah grassland from sea level to an elevation of 200 m.

Since the extent of its natural range is uncertain, N. thorelii is listed as Data Deficient on the 2006 IUCN Red List of Threatened Species based on an assessment carried out in 2000. 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.

Putative natural hybrids between N. mirabilis and N. thorelii have been recorded. Both simple and complex crosses with N. mirabilis are present at the Sữa Đá site, discovered in 2011.