AppearanceNepenthes kerrii is a climbing plant growing to a height of approximately 4 m. The stem is terete and 3–5 mm in diameter. It is typically self-supporting and unbranched. Internodes are up to 8.5 cm long. The stem ranges in colour from green to red.
Leaves are sessile and coriaceous in texture. The lamina (leaf blade) is obovate, measures up to 31 cm in length by 3 cm in width, and is around 0.5 mm thick. Its apex is acuminate and it is attenuate at the base, clasping the stem for around three-quarters of its circumference. Three longitudinal veins are present on either side of the midrib, restricted to the distal quarter of the lamina. Pinnate veins are also visible, and arise obliquely from the midrib. Tendrils are up to 30 cm long and 3 mm in diameter. They are coiled in upper pitchers. The laminae are light green, while the midrib and tendrils may be green to red.
Rosette and lower pitchers are either wholly ovate or only ovate in the basal half of the pitcher cup and narrower above. They measure up to 14 cm in height by 6 cm in width. The hip, which is only faintly visible, is positioned either in the middle or in the upper half of the trap. A pair of wings (≤8 mm wide) runs down the ventral surface of the pitcher cup, bearing narrow fringe elements. The pitcher mouth is oval and has an oblique insertion. The peristome is cylindrical and up to 12 mm wide, with teeth up to 0.5 mm long. The pitcher lid or operculum is round with a slightly cordate base and an irregularly wavy margin. It measures up to 4.3 cm in length by 4.7 cm in width, being as large as the mouth. The lower surface of the lid does not have any appendages, but bears numerous crater-like glands (≤1 mm in diameter), the largest of which are located around the midline. The spur, which is inserted near the base of the lid, is up to 7 mm long and may be simple or branched. Terrestrial pitchers are typically orange with red blotches on their outer surface. These red markings are also found in the waxy zone of the inner surface. The peristome and lid range in colour from orange to red.
The tubulose upper pitchers are similar in size to their terrestrial counterparts, measuring up to 15 cm in height by 3.5 cm in width. The wings are up to 4 mm wide and spaced 4–6 mm apart. The pitcher mouth is orbicular or broadly ovate and has an oblique insertion. The peristome is lobate and has a distinct neck. The lid as well as other parts of the pitcher are similar to those found in terrestrial traps. Aerial pitchers have a lighter pigmentation than their lower counterparts, being green to yellow on the outer surface. Red blotches are present on the waxy inner surface. The peristome may be yellow or red striped, while the lid is green to yellow and commonly red on its lower surface.
Nepenthes kerrii has a racemose inflorescence up to 130 cm long. In male plants, the inflorescence reaches 90 cm in length, of which the peduncle can constitute up to 65 cm and the rachis up to 27 cm, and bears around 120 flowers singly on pedicels measuring 6–8 mm in length. The androphore is up to 1.5 mm long. Tepals are round or elliptic and up to 4 mm long by 3 mm wide. Those of male flowers may be green or red, whereas those of females are always green. The female inflorescence is similar in structure to the male one, but differs in having a rachis up to 25 cm long with longer pedicels of 10–23 mm. Nepenthes kerrii exhibits modified seed morphology, whereby the seed wings are significantly reduced. This is thought to be an adaptation to the species's island habitat; the lack of prominent seed wings likely serves to prevent strong winds from blowing them into the sea.
An indumentum of brown hairs (0.1 mm long) is present on the leaf axils and inflorescence.
Like all pyrophytic Nepenthes from Indochina, N. kerrii has a well-developed rootstock.
NamingThe specific epithet kerrii refers to Irish medical doctor Arthur Francis George Kerr, who made the first known herbarium collection of this species.
DistributionNepenthes kerrii is endemic to Tarutao National Marine Park in Satun Province, southern Thailand. Reports of this species from the Malaysian island of Langkawi represent a different, although similar, taxon. The species has an altitudinal range of 400–500 m above sea level.
HabitatIts typical habitat is open savannah and grassland, where it grows terrestrially in sandy soil. This soil consists of a quartz-rich layer up to 30 cm deep over a base of granite. During the dry season, this substrate can become very hot and dry, hardening considerably as a result. Nepenthes kerrii is not sympatric with any other Nepenthes species in the wild and no natural hybrids involving it have been recorded.
In Pitcher Plants of the Old World, Stewart McPherson writes that populations of N. kerrii "are extremely inaccessible and not threatened at present".
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