Mitochondrial complex III (CIII) and complex IV (CIV), which can associate into a higher-order supercomplex (SC III+IV), play key roles in respiration. However, structures of these plant complexes remain unknown. We present atomic models of CIII, CIV, and SC III+IV from determined by single-particle cryoEM. The structures reveal plant-specific differences in the MPP domain of CIII and define the subunit composition of CIV. Conformational heterogeneity analysis of CIII revealed long-range, coordinated movements across the complex, as well as the motion of CIII's iron-sulfur head domain. The CIV structure suggests that, in plants, proton translocation does not occur via the H channel. The supercomplex interface differs significantly from that in yeast and bacteria in its interacting subunits, angle of approach and limited interactions in the mitochondrial matrix. These structures challenge long-standing assumptions about the plant complexes and generate new mechanistic hypotheses.