Nepenthes Dubia - Botanical History

Botanical History

Nepenthes dubia was first collected on May 29, 1917 by H. A. B. Bünnemeijer on Mount Talakmau, at an altitude of around 1900 m above sea level. Eleven years later, B. H. Danser formally described N. dubia in his seminal monograph "The Nepenthaceae of the Netherlands Indies". Danser noted similarities between N. dubia and the closely related N. inermis and suggested that it might represent a natural hybrid involving this species. He wrote:

N. dubia strongly resembles the striking N. inermis, but the difference is too large to unite these two species. N. inermis, like N. Lowii has only a rudiment of a peristome. N. dubia has a broad and flat one. There are, however, also differences in the other parts: the pitchers are less widely infundibuliform and the lid is not so narrow as in N. inermis. Perhaps N. dubia is a hybrid of N. inermis and another species with normal peristome and in that case N. Bongso could be the other parent species, the more so as the vegetative parts of N. inermis, N. dubia and N. Bongso are very similar, and between the other species of the gymnamphora-group intermediate forms often occur.

Danser based his description on the specimen collected in 1917, Bünnemeijer 938. It consists of a portion of a climbing stem with upper pitchers. The specimen is deposited at the Bogor Botanical Gardens (formerly the Herbarium of the Buitenzorg Botanic Gardens) in Java and Herbarium Lugduno-Batavum in Leiden, Netherlands. Bünnemeijer 938 was later designated as the lectotype of N. dubia by Matthew Jebb and Martin Cheek.

Renewed interest in Nepenthes in the latter half of the 20th century saw N. dubia become the subject of both confusion and taxonomic revision.

In an article published in 1973 on the Nepenthes of Borneo, Singapore, and Sumatra, botanist Shigeo Kurata incorrectly identified specimens of a natural cross between N. inermis and N. talangensis as belonging to N. dubia. Kurata would later describe this hybrid as a new species, N. pyriformis.

In 1986, Mitsuru Hotta and Rusjdi Tamin included plant material belonging to N. dubia and N. inermis in their description of N. bongso. However, N. bongso differs considerably in pitcher morphology from these species and is not easily confused with them.

In 1997, Matthew Jebb and Martin Cheek published their monograph "A skeletal revision of Nepenthes (Nepenthaceae)", in which they referred to N. dubia specimens from Mount Talang (Kurata s.n. SING) and the mountains of the Tjampo region near Payakumbuh (Meijer 6949 L). The latter specimen is the holotype of N. tenuis, which Jebb and Cheek treated in synonymy with N. dubia.

However, subsequent authors have rejected this interpretation. Charles Clarke restored N. tenuis to species rank in Nepenthes of Sumatra and Peninsular Malaysia (2001), citing differences in pitcher morphology. Clarke also identified Kurata s.n. as the natural hybrid N. × pyriformis, which is similar to N. dubia, but can be distinguished on the basis of several stable characters. The hybrid has a wider pitcher lid that is never relfexed beyond 90 degrees and the pitcher cup is not appressed in the lower parts as in N. dubia. In addition, the mouth of N. × pyriformis is raised towards the back as opposed to being horizontal.