2.1.1. Taxonomic Description of Nepenthes aenigma
Philippines, Luzon, Ilocos Norte, 17.06.2009, M. Calaramo, holotype Calaramo2288 (female flower) (HNUL, isotype HNUL)
Additional material examined:
Calaramo2270 (male flower) (24.6.2011, M. Calaramo
Differs from Nepenthes ventricosa Blanco in having cylindrical, winged and dimorphic pitchers, linear to elliptic lamina and 2-flowered partial peduncles (N. ventricosa: pitchers waisted at the middle, wings reduced to ridges, long and narrow lamina, inflorescense with 1-flowered partial peduncles).
was previously documented as an incompletely diagnosed taxon under the name N. sp. “Luzon”
A terrestrial, climbing vine. Stems
up to 5 m long, glabrous, terete to triangular in transection, 5 to 6 mm in diameter; internodes are up to 5 cm in length. There are dormant buds situated 3 to 5 mm above each leaf base. The vining stems produce short stems formed above the ground, which produce traps nested or buried in leaf litter. Aged stems eventually die off at the tips but the growing point is taken up by aerial shoots which sprout from the aforementioned dormant buds and which grow rapidly and produce traps. One of the photographs originally taken from these plants, taken at the time of the discovery of the species, clearly shows this behavior [11
Leaves are sessile, linear to ensiform with rounded to acute apices. They are up to 19 cm long by 5.4 cm wide and with 3 to 4 nerves on either side of the midrib; bases are strongly decurrent to the stems where they form narrow wings.
Lower pitchers are unknown. Intermediate pitchers originate abruptly from the tendril, which is at the side or the rear of the pitcher. Tendrils are 35 cm long, uncoiled and approx. 2 mm in diameter. The intermediate pitchers are barrel-shaped though the profile is slightly more elongated on those that are not buried in leaf litter. They are entirely cylindrical in transection and without a hip. They are 11.7–15.9 cm high by 4.1–6 cm in diameter. Wings are 4.5 mm wide with fringes often branched and measuring up to 4.85 mm long. The pitcher opening is circular and oblique to an angle of about 40 degrees when viewed from the sides. The lid is 41–48 mm long by 37–41 mm wide and has a cordate base. Lid glands are oblong, without borders and arranged in a V-like manner. The peristome is rounded in transection, up to 7 mm wide from the front of the mouth to 8.5 mm in breadth near the lid. Beneath the lid, the peristome is appressed to form a short neck. Peristome ribs are 0.5 mm high and spaced 0.8 mm apart. Inner edges of ribs end in downward pointing teeth up to 0.8 mm long from those near the lid but shorter elsewhere. Outer peristome margins are curved and slightly crenellated. The spur is 2.5 mm long and bifid at the tips.
Upper pitchers originate rather abruptly from the tendrils but less so than those in intermediate pitchers; they are cylindrical and slightly curved forward with the bases widely infundibular; 7.1 to 11 cm high by about 3 cm wide near the pitcher mouth. The peristome is somewhat flattened, 4.7 mm wide and broadening to 6.2 mm near the lid. Peristome ribs are 0.5 mm high and spaced 0.7 mm apart. Inner margins bear barely discernible teeth; outer margins are only moderately curled and only sparsely crenellated. The pitcher opening is circular and oblique to 30 degrees from the horizontal. The lid is oblong with cordate base, hardly keeled beneath, lacks an appendage and is 29 mm long and 25 mm wide. Lid glands are more numerous near the lid base, crateriform but very tiny. Wings are 2.4 mm wide with filaments up to 2.9 mm long, end abruptly at ⅔ to ⅞ of the pitcher length and as such do not reach the pitcher mouth. Higher up, the wings are reduced to narrow ridges. Sometimes, these wings are not symmetrical, one wing being markedly longer than the other one on the same pitcher. The spur is simple and 1.8 mm long. Tendrils are twice coiled.
The inflorescence develops from the axils, sub-terminal on stem. The male inflorescences measure 15–30 cm with mostly two-flowered partial peduncles. It is pubescent with flowers 6–9 mm in diameter; the pedicel is 6–8 mm long. Four tepals are present with elliptic apex and acute bases to 5 mm long; staminal column 4–5 mm long. Female flowers have an elliptic corolla, with bases and apices acute. Four pistils are present with fused apices, being white in color. The infructescence is unknown.
Indumentum is not significantly present; the plant is mostly glabrous, but short (0.35 mm), brown hairs are found on undeveloped traps and their subtending tendrils. In opened pitchers, indumentum is confined to the spur.
The color of the stems is bright green to dark reddish; the leaves are green with green midribs adaxially, green to red abaxially. Intermediate pitchers are pale green with elongated vertical dark red spots that often coalesce into larger blotches and which are densest underneath the lid. Lids are pale green with numerous tiny red spots that are mostly distributed on the margins. The peristome is cream to reddish, less commonly dark red, on those traps that form on the ground but is green with dark red suffusion on aerial pitchers. Upper pitchers are entirely green. Tendrils of intermediate pitchers are colored red, and green on the upper traps.
The morphological characteristics of N. aenigma
and its related species are summarized in Table 1
. Figure 1
shows a botanical illustration of N. aenigma
. Photos of the species at the type locality are shown in Figure 2
The specific epithet is derived from the Latin word aenigma
, which means ”puzzling”, a reference to the very unusual ecological preferences of this new taxon. (see Section 2.1.2
and Section 3
2.1.2. Distribution and Ecology
Nepenthes aenigma is so far only known from three sites on two mountains in Ilocos Norte Province, island of Luzon. Site 1 and 2 are only some 100 m apart on the same mountain, with unfragmented surrounding vegetation. Site 3 is located on another mountain 10 km apart.
grows terrestrially in leaf litter at altitudes ca.
1200 m a.s.l. in deep shade in windswept ravines. The vegetation where the observed populations occur consists mostly of dense stands of bamboo, interspersed with various species of rattan and Pandanus
. The vining plants have been seen to scramble and climb over these often spiny plants (Figure 2
D), but were not seen to direct their growing tips and reach for brighter light. A mossy forest formation is absent despite the elevation in which this new Nepenthes
occurs. This new taxon grows sympatrically with N. ventricosa
, at least on Site 1, but separated by a narrow band of altitude, the latter often growing at slightly higher elevations. The plants from Site 2 have not been observed to grow sympatrically with other Nepenthes
species. The single plant from Site 3 may be a representative of a larger population still awaiting discovery, and its flowering period is so far unknown. The mountain range in which these two species occur is quite extensive; the Northwesterniana Expeditions led by MC in the past years have tried to fill our gap in the knowledge of our plants in the area, but a sizable portion of the range remains little explored. Prey contents of the pitchers consisted mostly of ants, although unidentified spiders and roaches in advanced stages of decomposition were also noted. The traps also hosted unidentified mosquito larvae.
2.1.3. Conservation Notes
Only five plants were observed on Site 1 in 2013, all of which were in their vining stages. The plants are extremely difficult to locate due to their preference for dense vegetation, and the two mountains on which they have been found are seldom climbed, even by locals or mountaineers. Even so, we are reluctant to reveal the name of the peaks as an added precaution against poaching.
All plants from Site 1 observed in 2015 were males, and no seedling plants were observed, even in 2013. This fact, coupled with the very low population density perhaps points to a natural extinction of this species on this site. Site 2 consisted of two very small populations, and Site 3 yielded a single plant.
Based from the very low number of plants found, it is easy to assess N. aenigma
as “Critically Endangered” (CR) under IUCN [13
], but it should be noted that all plants from the three known sites are not in any way threatened by poaching or habitat disturbances. Pending further population studies of this species, we recommend that N. aenigma
be deemed “Data Deficient” (DD) with regards to its conservation status.