New Guinea. Nevertheless, it would be difficult to confuse these species as they have little else in common and are geographically isolated from each other. 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 a portion of the resultant cladogram, showing "Clade 5". It comprises the sister pair of N. eustachya and N. mirabilis with 72% support, as well as a weakly supported subclade (69%) that includes N. longifolia and the sister taxa N. rafflesiana and N. sumatrana with 58% bootstrap support. Natural hybrids Nepenthes eustachya is known to hybridise with a number of other Nepenthes species with which it is sympatric. Nepenthes albomarginata and N. eustachya grow in mixed populations at a number of locations in the Padang Highlands and Tapanuli. Natural hybrids between them appear to be relatively common around the river Tjampo in West Sumatra. A young plant of N. albomarginata × N. eustachya pictured in Nepenthes of Sumatra and Peninsular Malaysia was observed by Charles Clarke in 1998 on Bukit Kambut in West Sumatra. It grew in secondary vegetation amongst a population of N. eustachya at an elevation of around 900 m. This plant was subsequently destroyed, but Clarke and Troy Davis found a number of other plants on Bukit Tjampo. The hybrids were growing in a dense thicket of ferns (Dicranopteris linearis and Dipteris sp.) at approximately 750 m. Nepenthes albomarginata × N. eustachya often produces reddish leaves and pitchers. The characteristic white band of N. albomarginata is present just below the peristome. In common with N. eustachya, the indumentum is almost completely absent from the leaves, which are sub-petiolate and wider than those of N. albomarginata. No mature plants of this hybrid have been observed and, as such, the upper pitchers and inflorescence remain unknown. Nepenthes eustachya × N. longifolia has been recorded from a number of locations near Payakumbuh and Sibolga, where its parent species are sympatric. It is relatively rare because N. eustachya and N. longifolia occur in markedly different habitats; the former usually grows in exposed, sunny sites, while the latter is more common in dense, shady forest. This hybrid differs from N. eustachya in having fringed lamina margins bearing short reddish-brown hairs. The peristome often has a distinctive raised section at the front, a characteristic inherited from N. longifolia. It can be distinguished