Quantitative morphometrics suggest that the widespread Neotropical Humiria balsamifera (Aubl.) St. Hil. is a species complex

Jerome Chave,Alberto Vicentini,Charles E. Zartman,Ana Sofia Sousa de Holanda,Fernanda Antunes Carvalho

doi:10.1590/0102-33062020abb0368

Abstract

Humiria balsamifera is an infraspecific complex of high phenotypic variation and widely distributed in northern South America. Leaf traits are traditionally considered the most relevant taxonomic characters for varietal level delimitation in the group. However, substantial phenotypic overlap among vegetative characters complicates taxonomic diagnoses in this complex. The objective of this study was to quantify and analyze phenotypic variation among individuals of the complex at a continental scale using uni- and multivariable analyses to assess whether morphometric analyses detect discontinuities. Secondarily, these quantitative data were used to test whether phenotypic similarity was related to geographic distance. Twenty- five quantitative and 27 qualitative character traits did not overtly reveal a topology corresponding to traditional varietal classification, nor to geographic structure. However, petiole length alone revealed a definitive separation of H. balsamifera var. guianensis (together with another recognized species Humiria wurdackii, and variety H. balsamifera var. laurina) from the rest of the taxa. Our results highlight substantial morphological overlap among vegetative and reproductive characters including those used in identification keys, and no morphological discontinuities suitable for clearly separating taxa within the complex were encountered demonstrating a future need to integrate multiple sources of information, including molecular data, to resolve this complex.

Highlights

The tropics, which have been exposed to long periods of frequent climatic variation over large areas (Wang et al 2017), are likely to harbor many poorly connected populations through propagule dispersal producing “species complexes”: groups of individuals which present wide phenotypic variation, yet lack perceivable discontinuities among potential taxonomic units (Grube & Kroken 2000; Prata et al 2018)
The objective of this study was to quantify and analyze phenotypic variation among individuals of the complex at a continental scale using uni- and multivariable analyses to assess whether morphometric analyses detect discontinuities
Some characters suggest discontinuities within H. balsamifera: i) petiole lengths are larger in H. balsamifera var. guianensis, this group includes another species H. wurdackii within its range of phenotypic variation (Fig. S1A in supplementary material); ii) blade widths are wider in varieties H. balsamifera var. balsamifera, H. balsamifera var. floribunda, and H. balsamifera var. guianensis (Fig. S1D in supplementary material) which share more ovate leaf forms when compared to H. balsamifera var. laurina, and H. wurdackii

Summary

Introduction

The tropics, which have been exposed to long periods of frequent climatic variation over large areas (Wang et al 2017), are likely to harbor many poorly connected populations through propagule dispersal producing “species complexes”: groups of individuals which present wide phenotypic variation, yet lack perceivable discontinuities among potential taxonomic units (Grube & Kroken 2000; Prata et al 2018) Such groups of high phenotypic variation are relatively common and offer, due to their high phenotypic overlap, demonstrably difficult challenges to traditional classification (Jacobs et al 2019; Damasco et al 2019). The task of identifying such species groups is the first step towards understanding the mechanisms and processes of speciation in the richest plant biome on the planet: the Amazon Basin

Objectives

Methods

Results

Conclusion