Range in excitation temperatures (shaded colored areas) for all detected species toward the embedded low-mass protostellar systems in the JOYS sample. For each species, the measured range of more evolved Class II sources is presented in the shaded gray areas (Salyk et al. 2011; Grant et al. 2023; Gasman et al. 2023; Tabone et al. 2023; Temmink et al. 2024a; Schwarz et al. 2024; Arabhavi et al. 2024). Since no data are available for SiO, SO₂, CS, and NH₃ in Class II sources, these are not displayed. It is evident that the molecular features in Class 0&I sources are tracing colder regions than in Class II sources, although the number of detections in embedded sources remains limited.