Nepenthes Tenuis - Taxonomy

Taxonomy

In their 1997 monograph, Matthew Jebb and Martin Cheek reduced N. tenuis to a synonym of N. dubia "with some hesitation". Material representing the natural hybrid N. inermis × N. talangensis (N. × pyriformis) was also identified by the authors as belonging to N. dubia. However, this interpretation is not followed by Charles Clarke, who does not consider the three taxa to be conspecific.

Nepenthes dubia and N. tenuis can be distinguished with relative ease. Most obviously, the pitchers of N. tenuis have shorter, broader lids that are never reflexed beyond 180°, unlike those of N. dubia, which are always reflexed beyond 180°. The pitchers of N. tenuis are also differently coloured, often having red flecks on the outside, in contrast to those of N. dubia, which are usually a solid yellow or orange colour. The peristome of N. tenuis is also less tightly cylindrical than that of N. dubia.

Nepenthes tenuis can be distinguished from N. jacquelineae by its linear-lanceolate leaf blade (as opposed to ovate-spathulate in the latter) and lack of large glands on the lower surface of the lid. The lid of N. jacquelineae also differs by being noticeably contracted towards the base. Finally, N. jacquelineae is far larger in stature compared with N. tenuis and its pitchers have a far more developed and broader peristome that is almost horizontal.

In their description of the species, Nerz and Wistuba included a table of "characteristics which clearly distinguish Nepenthes tenuis from similar species":

Charles Clarke writes that "the obvious similarities between N. tenuis, N. talangensis and N. jacquelineae are suggestive of recent adaptive radiation, and add further weight to the argument that the non-volcanic mountains of Bukit Barisan are the primary source of morphological diversity in Sumatran Nepenthes".

In 2001, Clarke performed a cladistic analysis of the Nepenthes species of Sumatra and Peninsular Malaysia using 70 morphological characteristics of each taxon. The following is part of the resultant cladogram, showing "Clade 1", which has 51% bootstrap support. Its most strongly supported subclade is the sister pair of N. inermis and N. dubia, having 95% support.