Linking leaf spectra to the plant tree of life

Evolutionary trees recount the history of how biological diversity came to be and how evolution gave rise to the incredible variation in plant form and function that can be captured by spectral reflectance. Understanding plant spectra in light of evolution is thus important for assessing biodiversity and critical for explaining how spectral diversity is generated. Here, we focus on leaf spectra and how they are linked to the plant tree of life. We review what evolutionary trees (phylogenies) are and how to interpret them. We then describe how to model the evolution of quantitative traits, discuss which evolutionary processes are involved, and explain specific concepts and metrics, such as phylogenetic signal and evolutionary rates, and how they can be applied to reflectance spectra. Next, we describe a framework that links phylogenies and leaf spectra by coupling models of evolution and radiative transfer models. In doing so, we review some of the challenges of subjecting spectra to evolutionary analyses. We then discuss how spectra can help us to understand leaf evolution and to differentiate plant taxa at different phylogenetic scales from populations to lineages, advancing our potential to remotely detect biodiversity.