Phylogenetic analyses have revealed extensive evolutionary lability of morphological characters in the large genus Impatiens. This potentially complicates taxonomic classifications, especially if these are based on analyses which include a limited number of characters and taxa. In this study we focus on the systematics of previously poorly represented Impatiens from Southeast Asia, a hotspot of species diversity, using an expanded taxon sampling. Specifically we implement phylogenetic analyses of DNA sequences from the nuclear ITS and plastid atpB-rbcL intergenic spacer and reconstruct the evolution of several morphological characters to study Semeiocardium, a taxon which has been recognized as a distinct genus, subgenus, and section in previous taxonomic treatments. Both Bayesian and Parsimony analyses demonstrated that Impatiens subg. Semeiocardium is not monophyletic. Thirteen representatives are part of a large clade, which also includes many other Southeast Asian taxa. Connate lateral united petals are a synapomorphy of this clade, while a four-locular ovary and connate outer lateral sepals are not. Impatiens muscicola and I. santisukii, which were previously classified under I. subg. Semeiocardium, do not belong to the clade with connate lateral united petals or to I. sect. Semeiocardium. Due to ambiguous combinations of morphological characters we could not determine whether sampled species belonged to I. sect. Semeiocardium. In addition to the characters that were used to diagnose I. sect. Semeiocardium, we identify connate lateral united petals as a taxonomically useful character to distinguish an additional monophyletic clade in I. sect. Semeiocardium. Further research is needed to identify diagnostic characters for the sister clade comprising I. stenosepala and its allies.