There is emerging evidence that some C4 eudicots involve the photosynthetic enzyme PEP-CK in carbon acquisition alongside other decarboxylation enzymes. Muhaidat and McKown examine leaf ultrastructural characteristics together with enzyme activities and immunolocalizations in three C4 species, Trianthema portulacastrum, T. sheilae and Zaleya pentandra. They find involvement of PEP-CK in C4 NADP-ME T. portulacastrum and NAD-ME Z. petandra, and this occurs irrespective of biochemical sub-type or the position of bundle sheath chloroplasts. Ultrastructural traits, including numbers of bundle sheath peroxisomes and mesophyll chloroplasts, and degree of grana development in bundle sheath chloroplasts, coincide more directly with PEP-CK recruitment. The findings offer a unique opportunity for evaluating PEP-CK expression and suggest the possibility that PEP-CK recruitment may exist elsewhere in C4 eudicots.