Tropical pitcher plant (Nepenthes tobaica)

Description

Nepenthes tobaica /nɪˈpɛnθiːz toʊˈbaɪkə/ is a tropical pitcher plant endemic to Sumatra. It is particularly abundant around Lake Toba, after which it is named. Nepenthes tobaica is closely related to N. angasanensis, N. gracilis, N. mikei, and N. reinwardtiana. Nepenthes tobaica is a climbing plant. The stem can attain a height of up to 7 m and is up to 6 mm in diameter. Internodes are up to 25 cm long and often round in cross section. However, mature plants may have angular stems because of a groove that originates at the node and extends across most of the internode's length. Leaves are coriaceous in texture and range from sessile to sub-petiolate. The shape of the lamina, or leaf blade, varies from oblong to spathulate. It measures up to 20 cm in length by 4 cm in width. The apical end of the lamina is typically rounded, but may be narrowed and obtuse. Robust plants sometimes have a sub-peltate tendril insertion. The lamina may be gradually or abruptly contracted towards the amplexicaul base, which clasps the stem for around half of its circumference. One to three longitudinal veins are present on either side of the midrib, although they are only prominent in robust specimens. Pinnate veins are indistinct. Tendrils grow to 30 cm in length. Rosette and lower pitchers are ovoid in the lower portion and cylindrical above. They are up to 20 cm high by 4 cm wide. A pair of wings runs down the pitcher's ventral surface, often bearing fringe elements either throughout the whole length or only in the upper part. The glandular region of the pitcher's inner surface is confined to the ovoid portion. A pair of "eye spots" is sometimes present on the inner surface, below the lid attachment. The pitcher mouth is ovate and has an oblique insertion. The narrow peristome (≤5 mm wide) is cylindrical or slightly expanded and bears indistinct teeth. The pitcher lid or operculum is ovate to sub-orbicular and has a somewhat cordate base. It lacks appendages. A spur measuring up to 5 mm in length is inserted near the base of the lid. It may be unbranched, bifid, or trifid. Upper pitchers are typically somewhat infundibular in the lowermost part, becoming narrowly ovoid in the lower third, and finally cylindrical and slightly narrower above. They may be quite large, reaching 25 cm in height by 5 cm in width. The waxy zone of the inner surface is well developed. A pair of remnant ribs is present in place of the ventral wings. The inner portion of the peristome accounts for around 40% of its total cross-sectional surface length. Other parts of aerial pitchers are similar to their lower counterparts. Nepenthes tobaica has a racemose inflorescence. The peduncle and rachis can each grow to 20 cm in length. Partial peduncles are two-flowered and lack bracteoles. In male inflorescences, the sepals are elliptic-obtuse, being slightly narrower in female ones. Around the town of Prapat, plants have been observed to come into flower in April, although mature fruits are not common at this time. Nepenthes tobaica is characterised by an uneven indumentum. Most mature vegetative parts are glabrous, although the midrib may bear persistent hairs. Groups of white, stellate hairs are often present in the leaf axils. The sepals of this species are densely tomentose, but the rest of the inflorescence has a sparser covering of short hairs. In some forms, the underside of the lid is a vivid red, making the plants particularly easy to spot amongst other vegetation.