Eastern North America is a center of diversity for leiobunine harvestmen (daddy longlegs), but many species are poorly delimited or undescribed. My research attempts to bring taxonomic order to one newly circumscribed assemblage, here named the Leiobunum nigropalpi species group. It includes two named species, L. nigropalpi (Wood 1868) and L. calcar (Wood 1868), and several undescribed or problematic species. This research clarifies the taxonomy and morphological diversity of this group and delimits four morphospecies. Information is derived from traditional characters (e.g., male palps, penis, coxal denticles, ocularium) and newly discovered structures, such as those associated with the pregenital chamber in females. The results indicate that the nigropalpi species group contains four well-delimited morphospecies (namely, L. nigropalpi, L. hoffmani new species, L. euserratipalpe new species and L. calcar), although the latter two each encompasses substantial variation and may be paraphyletic.