Nepenthes Hamiguitanensis

''Nepenthes hamiguitanensis'' is a tropical pitcher plant endemic to a single peak on the Philippine island of Mindanao, where it grows at elevations of 1200–1600 m above sea level. Once thought to be a natural hybrid between '' N. micramphora'' and '' N. peltata'', this plant is now considered a species of possible hybridogenic origin.McPherson, S.R. 2010
Four new species of ''Nepenthes''
Carnivorous Plants UK, October 11, 2010. It produces squat upper pitchers that vary greatly in pigmentation, from red speckled to yellow throughout.

The specific epithet ''hamiguitanensis'' is derived from the name of Mount Hamiguitan, to which it is endemic, and the Latin ending '' -ensis'', meaning "from".

Botanical history

Although only formally described in 2010, this taxon was already known several years earlier. A herbarium specimen of ''N. hamiguitanensis'' was collected by Victor B. Amoroso and R. Aspiras on March 13, 2007, from the Mount Hamiguitan summit ridge, specifically the trail leading to San Isidro. This plant was growing in montane forest margins at an altitude of 1310 m. Designated as ''V.Amoroso & R.Aspiras CMUH00006494'', the specimen is deposited at the Central Mindanao University Herbarium (CMUH) in Musuan, Bukidnon, Mindanao, Philippines.

Thomas Gronemeyer, Volker Heinrich and Stewart McPherson carried out field studies on ''N. hamiguitanensis'' and the other species of Mount Hamiguitan between July 22–24, 2008. The taxon was subsequently identified as a natural hybrid between '' N. micramphora'' and '' N. peltata'' in McPherson's two-volume monograph, ''Pitcher Plants of the Old World'', published in May 2009.

Gronemeyer returned to the site with Andreas Wistuba between February 13 and 14, 2010. Numerous seedlings and mature, climbing plants of ''N. hamiguitanensis'' were observed, but no intermediate plants with lower pitchers were found. These field studies on Mount Hamiguitan also included observations of '' N. micramphora'', '' N. justinae''Gronemeyer, T., W. Suarez, H. Nuytemans, M. Calaramo, A. Wistuba, F.S. Mey & V.B. Amoroso 2016. Two new ''Nepenthes'' species from the Philippines and an emended description of ''Nepenthes ramos''. ''Plants'' 5(2): 23. (then regarded as a form of '' N. mindanaoensis''), and '' N. peltata''.

''Nepenthes hamiguitanensis'' was formally described by Thomas Gronemeyer, Andreas Wistuba, Volker Heinrich, Stewart McPherson, François Mey, and Victor B. Amoroso, in the second volume of McPherson's ''Carnivorous Plants and their Habitats'', published in July 2010. The herbarium specimen ''V.Amoroso & R.Aspiras CMUH00006494'' was designated as the holotype.

Description

''Nepenthes hamiguitanensis'' is a climbing plant growing to a height of 4 m. The stem is cylindrical and 8–10 mm in diameter in mature plants; internodes are 4–7 cm long.

Leaves of the climbing stem are petiolate. The lamina (leaf blade) is elliptic to oblong and measures up to 25 cm in length by 9 cm width. It has an obtuse apex, while the base is gradually attenuate, forming a canaliculate, sessile petiole up to 9 cm long. Three longitudinal veins are present on either side of the midrib. Pinnate veins are numerous and run obliquely to the laminar margin. Tendrils are often approximately the same length as the lamina; those bearing upper pitchers are often curled.

In the wild, no adult lower pitchers were recorded, and only rosette pitchers on seedling plants were recorded. For this reason they were not covered in the formal description.

Upper pitchers are infundibular in the basal half and cylindrical to slightly infundibular above. A prominent hip and waist (constriction) delimits these two halves. These aerial traps are up to 20 cm high by 9 cm wide. Wings are reduced to a pair of ribs on the ventral surface of the pitcher cup. The pitcher mouth (≤8 cm wide) has an oblique insertion and rises towards the rear, forming a short neck. The peristome is typically cylindrical but may sometimes be slightly flattened. It is up to 1 cm wide and bears ribs spaced 0.3 mm apart, which terminate in short teeth (≤1 mm long) on the inner margin. The glandular or digestive region covers the lower half of the pitcher's inner surface. The pitcher lid or operculum is cordate and up to 5 cm wide. Nectaries are evenly distributed on the underside of the lid and a prominent appendage is present at the base of the lid's lower surface. A bifurcate spur (≤4 mm long) is inserted near the base of the lid. Upper pitchers are most commonly creamy white throughout, but may also be red speckled on a yellowish background. The peristome may be creamy white, red striped, or dark red.

''Nepenthes hamiguitanensis'' has a racemose inflorescence. In the type description, the male inflorescence is recorded as being around 70 cm long by 3.5 cm wide and bearing two-flowered, ebracteate partial peduncles. These measurements are taken from field observations carried out by the describing authors at the type locality on July 23, 2008, since herbarium material of the floral structures could not be located.

An coarse indumentum of short, light brown to white hairs is present on all plant parts, being particularly prominent at the laminar margins.

Ecology

''Nepenthes hamiguitanensis'' is endemic to the summit ridge of Mount Hamiguitan in San Isidro, Davao Oriental, Mindanao, Philippines. It has an altitudinal distribution of 1200–1600 m above sea level, being particularly common at elevations above 1400 m.

The species grows terrestrially in primary montane forest and forest margins. It is not found in the so-called Bonsai Forest, a region of stunted vegetation on the plateau below the summit ridge of Mount Hamiguitan. It typically grows in partial shade and is frequently exposed to heavy downpours. While Mount Hamiguitan is an ultramafic mountain, ''N. hamiguitanensis'' does not necessarily grow in an ultramafic substrate, owing to the high humus content of the forest underlayer. At the type locality, ''N. hamiguitanensis'' occurs at an average density of around two to three plants per 50 m², as estimated by eye. Only seedlings and mature, climbing plants have been observed, with no records of larger rosette plants bearing lower pitchers.

''Nepenthes hamiguitanensis'' is sympatric with '' N. justinae'' (previously identified as '' N. mindanaoensis'') and grows in the same altitudinal range as '' N. micramphora'' and '' N. peltata''; the latter two species are typically found in more open areas, where they are exposed to higher levels of incident light. Despite this, no natural hybrids involving ''N. hamiguitanensis'' have been observed with certainty; it has been suggested that the flowering times of ''N. hamiguitanensis'' and the other ''Nepenthes'' species of Mount Hamiguitan may differ.

The describing authors assessed the conservation status of ''N. hamiguitanensis'' as Vulnerable based on the IUCN criteria. They pointed out that ''N. hamiguitanensis'' is far more localised than ''N. micramphora'' and ''N. peltata'', which occur at several sites on the mountain and are represented by larger populations. Mount Hamiguitan forms part of the Mount Hamiguitan Range Wildlife Sanctuary National Park and visitors are only permitted to climb the mountain with the assistance of a guide. The future of wild populations of ''N. hamiguitanensis'' will be further secured if provincial officials of Davao Oriental are successful in their bid to gain recognition of Mount Hamiguitan as a UNESCO World Heritage Site.

Hybrid origin

''Nepenthes hamiguitanensis'' was initially assumed to represent a natural hybrid between '' N. micramphora'' and '' N. peltata'', both of which are also present on the upper slopes of Mount Hamiguitan. It shares several morphological features with its putative

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