Vascular bundles in plants transport sugars, minerals and water, which is a limiting factor for yield realization. Huang et al. (pp. 81-90) report highresolution genetic analyses of the number of vascular bundles in maize stem using a large maize-teosinte population. Results showed that the vascular bundle number is controlled by a large number of small-effect QTLs that might not be under directional selection during domestication.