The significance of seed characters for the taxonomy and evolution of Impatiens (Balsaminaceae) in China

Abstract Background and Aims For Impatiens (Balsaminaceae), morphological characters of seeds are of great importance in classification. Nevertheless, the phylogenetic implications of seed coat cellular traits in Impatiens remain unexplored, particularly regarding their potential to elucidate divergent evolutionary trajectories among Chinese taxa. Methods Seed morphological characterization was performed on 145 Impatiens species using scanning electron microscopy. Quantitative analysis included: (1) seed shape, (2) primary and secondary testa ornamentation patterns, (3) testa cell arrangement, (4) ultrastructural features of main and accessory cells, and (5) the periclinal/anticlinal wall. Phylogenetic reconstruction was conducted using nuclear ITS sequences and combined ITS-atpB-rbcL datasets, with comparative analysis against chloroplast genome-derived phylogenies. Ancestral character state reconstruction and biogeographic analyses were implemented in both the ITS and chloroplast genome phylogenetic frameworks. Key Results We present the first comprehensive characterization of seed ultrastructural traits in Impatiens, quantifying (1) cellular arrangement patterns, (2) principal and accessory cell morphologies, and (3) surface ornamentation. Our combined analysis of macroscopic and microscopic morphology identifies new features for clade delimitation. We hypothetically reconstruct the migration routes of Impatiens during its early evolutionary period in the Chinese region. Conclusions The seeds of Impatiens are extremely diverse in both macromorphology (seed shape) and micromorphology (seed coat ornamentation, etc.), and this diversity is important not only taxonomically, but also for biological evolution and ecological adaptations.