Geometric morphometric analysis of two highland Nepenthes species and their natural hybrid

Abstract: Tropical pitcher plants of the genus Nepenthes are renowned for their highly specialized leaves, which form pitchers used to capture and digest prey. Pitcher morphology is remarkably diverse across the genus and serves as a primary feature for taxonomic studies, though its analysis is complicated by substantial intraspecific variation, morphological similarity among species, and the presence of natural hybrids. This study evaluates the effectiveness of geometric morphometric techniques using a minimal number of landmarks to quantify shape differences among N. villosa, N. edwardsiana, and their natural hybrid N. × harryana, as well as patterns of intraspecific variation. Using only 13 digitized landmarks, geometric morphometric analyses clearly distinguished N. villosa and N. dwardsiana, and positioned N. × harryana in an intermediate region of morphospace. Intraspecific variation differed between species, with significantly greater shape variation observed in N. villosa than N. edwardsiana, and a distinct morphological separation between pitchers from two mountain peaks in N. villosa. Although N. × harryana occupied an intermediate position overall, its morphology skewed toward N. edwardsiana rather than forming an exactly intermediate morphology. Comparisons between original species identifications and morphology based assignments showed broad agreement, with discrepancies primarily involving N. villosa from Mt. Tambuyukon and several N. × harryana that may reflect introgression. Overall, these results demonstrate that streamlined geometric morphometric approaches provide a robust and efficient framework for analyzing Nepenthes morphology.