Innovative multi‐scale approach to study the phenotypic variation of seedling leaves in four weedy <i>Amaranthus</i> species

Plant phenotyping on morpho-anatomical traits through image analysis, from microscope images to large-scale acquisitions through remote sensing, represents a low-invasive tool providing insight into physiological and structural trait variation, as well as plant-environment interactions. High phenotype diversity in the genus Amaranthus includes annual weed species with high invasiveness and impact on important summer crops, and nutritive grain or vegetable crops. Identification of morpho-anatomical leaf characters at very young stages across weedy amaranths could be useful for better understanding their performance in agroecosystems. We used an innovative multi-scale approach with phenotype analyses of about 20 single-leaf morphometric traits of four Amaranthus species through processing confocal microscopy and camera acquisitions. The results highlight that determination of leaf traits at different investigation levels highlight species-specific traits at a juvenile stage, which are crucial for plant development, competition and establishment. Specifically, leaf circularity and hairiness Aspect Ratio better discriminated A. tuberculatus from other species. Also, leaf DW, hairiness area and perimeter variables allowed identification of dioecious amaranth species as distinct from monoecious species. The methodology used here provides a promising, reliable and low-impact approach for the functional characterization of phylogenetically related species and for statistical quantification of traits involved in taxonomy and biodiversity studies.