Soybean is trifoliolate, but 4-, 5-, or 6-foliolate leaves have been reported and expression of such multi-foliolate (MF) leaf forms has been shown to be heritable. Here we analyze the genetic complexity of the MF phenotype and the dependence of its expression on the environment. Recombinant inbred (RI) segregants of soybean were grown in different environments. The frequency of plants expressing the MF phenotype as well as the frequency of nodes exhibiting MF leaves varied with both the environment and the RI segregant genotype. Growth chamber experiments supported field observations suggesting that environment (day length, temperature, etc.) at emergence influenced expression of MF during subsequent growth. Marker facilitated analyses of three RI segregant populations identified quantitative trait loci (QTLs) in 17 regions of the soybean genome. These either directly regulated MF phenotype expression, or were involved in interactions with such loci. Loci, identified in one RI population also were identifiable in another, different, RI population. Most of the loci affected both the frequency of plants expressing MF, and the number of nodes on MF plants that expressed the phenotype. However, a few loci differentiated between these two effects. Many loci affected plants in both field experiments, however, a few differentiated between the two environments. Similar patterns were observed for interactions between loci. QTLs regulating the MF phenotype were located in genome regions that also contained QTLs regulating major agronomic traits-e.g. yield, lodging, etc. This suggests that the loci involved regulate plant growth at some over-arching level, controlling multiple phenotypes or traits.