"Nepenthes ovata" is thought to be most closesly related to "N. bongso". The glandular crest that is so characteristic of "N. ovata" has also been observed in some forms of "N. bongso". Charles Clarke writes that he is "reluctant to distinguish "N. ovata" from ["N. bongso"] using this criterion only and unable to suggest any other features that might serve this purpose". However, he retains "N. ovata" as a distinct species, noting that although the appendage may be present in "N. bongso", this is rarely the case and even then it is usually less developed than in "N. ovata".