A genus of 5 species, annual and perennial herbs, temperate, of e. North America (Plunkett et al. 2018a). Ptilimnium should be re-split into two genera, Harperella and Ptilimnium; as Ptilimnium (s.s.) with compound leaves is more closely related to Tiedemannia (formerly Oxypolis with quill leaves) than it is to Harperella (Feist & Downie 2008; Feist et al. 2012).
Ref: Easterly (1957); Feist (2010); Feist & Downie (2008); Feist et al. (2012); Feist et al. (2012); Kral (1981a); Kress, Maddox, & Roesel (1994); Mathias & Constance (1945); Plunkett et al. (2018a) In Kadereit & Bittrich (2018); Weakley & Nesom (2004). Show full citations.