Abstract text: Trees capture carbon dioxide and construct secondary cell walls with differing amounts of cellulose, matrix polysaccharides and lignin. These polymers make up hardwood xylem: longitudinal vessels and fibers, and radially aligned ray parenchyma. Wood can be manipulated through chemical and physical treatments to surpass its mechanical limitations. However, prior studies focused on optimizing these modifications to produce sustainable construction materials, rather than exploring how cell anatomy and wall composition contribute to wood mechanical properties. We examined the anatomy and wall composition of five hardwood species local to the Northeastern United States, as well as poplar mutants with genetically modified lignin biosynthesis. Using laser ablation tomography and compression testing, we found that large ray parenchyma enhances radial stiffness, but does not fully explain variation in stiffness across hardwoods. This prompted us to investigate interspecies variation in lignin structure in xylem. Histochemical analyses revealed no significant differences in S:G lignin ratio or aldehyde residue absorbance in Northeastern hardwoods. On the other hand, accumulation of lignin alcohol residues correlated with enhanced poplar stiffness. Together, these data demonstrate that variation in cell anatomy and accumulation of specific lignin residues affect mechanics, information which can support efforts to transform wood into carbon-negative building materials.