Elliptic Fourier Analysis of leaf outlines in five species of Heteropsis (Araceae) from the Reserva Florestal Adolpho Ducke, Manaus, Amazonas, Brazil

Abstract

A pilot study of leaf outline morphometrics was carried out on populations of five species of Heteropsis located in the Reserva Florestal Adolpho Ducke near Manaus, Amazonas, Brazil: H. flexuosa (Kunth) G. S. Bunting, H. macrophylla A. C. Sm., H. spruceana Schott, H. steyermarkii G. S. Bunting and H. tenuispadix G. S. Bunting. The aim of the study was to investigate quantitative methods for discriminating species within a local area based on vegetative morphology in a genus where fertile parts are often difficult to find in the field; this study focussed on leaf outline shape. Using digital images of 347 leaves, outlines were captured as coordinates using the TpsDig software and analysed using Elliptic Fourier Analysis (EFA). Principal Component Analysis (PCA) was used to reduce the 160 elliptic Fourier coefficient descriptors to a smaller number of independent shape variables corresponding to the principal component axes. The first nineteen shape variables (constrained by the smallest species sample, N = 20) were then subjected to Linear Discriminant Analysis (LDA) to find new axes that would discriminate the five species to the maximum extent. The first six shape variables were visualised by a reification procedure in order to illustrate their characteristic contribution to the total shape variation within all five species. The results showed that the mean shapes of all five species were significantly different, but shape variation within each species overlapped with the others. Percentage assignment of individuals to their correct species was encouragingly high given that only outline shape was used, but was not high enough overall to provide reliable identification. Elimination of one species (H. steyermarkii) using easily observed qualitative vegetative characters improved discrimination of the remaining four. The investigation of new approaches to identification is potentially valuable for conservation of natural populations — the root fibre of Heteropsis is extracted from primary forest and is a valuable non-timber forest product that forms the basis for an important local industry in Amazonia.