Elliptic Fourier analysis of leaf shape in southern AfricanStrychnossectionDensiflorae(Loganiaceae)

Abstract

Leaves can be a useful source of taxonomic information in plants particularly when flowers and fruits are absent during certain periods of the year. In this study, we applied an elliptic Fourier analysis (EFA)-based morphometric technique to assess leaf morphological divergence among four species of southern African Strychnos section Densiflorae. Using leaf specimen images from field and herbarium collections, we extracted six shape variables [i.e. principal components (PCs)] from the Fourier coefficients and used these variables to describe leaf outline among the species. Our results indicate that the symmetric component of a leaf is the main source of shape differences accounting for 90.25% of total leaf shape variation and captures the more obvious range of observed shapes. PC1 of the symmetric variables describes a wide range of visually observable leaf shape among the species. MANOVA revealed significant interspecific differences except between S. innocua and S. madagascariensis, which could not be separated by outline analysis. A cross-validated group classification suggests that S. gerrardii, with a classification rate of 88.4%, is distinct from S. madagascariensis, contrary to some taxonomic treatments. We discuss the value of geometric morphometrics at detecting subtle morphological variations and the evolutionary implications of such variations, which may be undetectable to the human eye.

Evolution of the leaf economics spectrum in herbs: Evidence from environmental divergences in leaf physiology acrossHelianthus(Asteraceae)

“…The diversity of leaf shape seen across Helianthus appears to arise primarily through the modulation of lateral width, with the first principal components axis explaining 81% of phenotypic variation in leaf shape. Very similar results were found using the same approach for the shrub genus Viburnum (Schmerler et al., ), as well as in southern African members of the genus Strychnos (Adebowale et al., ), for both of which the first principal components axis also captured modulation of leaf width and explained 85–91% of variation in leaf shape. Work in Arabidopsis has shown that four key genes control much of the variation in the leaf length/width ratio by affecting the shape of cells and the number present in the lamina (Tsukaya, ; Nicotra et al., ).…”

Analyzing Fluctuating Asymmetry with Geometric Morphometrics: Concepts, Methods, and Applications

“…This method for separating symmetric and asymmetric components of variation has been used in studies to characterize asymmetry and shape variation in plant leaves and other structures [191,260,[299][300][301][302][303][304].…”

Effectiveness of modern leaf analysis tools for the morpho‐ecological study of plants: the case of Primula albenensis

“…GMM methods are used in many disciplines, within and beyond plant biology, and allow the analysis of the relative positions of landmarks and sets of points used to approximate curves (outlines) and surfaces to quantify size and shape (Jensen 2003, Claude 2008). In recent years botanists have also applied these types of analysis to study the shape of leaves (Jensen 1990, Jensen et al 1993, Viscosi et al 2009a, b, Asanidze et al 2011, Adebowale et al 2012, Morello and Sede 2016, Chitwood and Otoni 2017, De la Paz Pollicelli et al 2018, Li et al 2018, Morello et al 2018, Sandner et al 2019) and other plant organs (Yoshioka et al 2004, Van der Niet et al 2010, Hernández-Ramírez and Aké-Castillo 2014, Ros et al 2014, Bonhomme et al 2017, Savriama 2018, producing informative results with tools which are relatively simple to use. Leaf analysis, compared to the analysis of other plant organs, can, however, with equally simple tools, also provide useful information on the ecology of species.…”