families, only two of which were in Cronquist's construction, and placed the order in the superorder Rutiflorae: family Zygophyllaceae family Nitrariaceae family Peganaceae family Balanitaceae family Erythroxylaceae family Humiriaceae family Linaceae family Ctenolophonaceae family Ixonanthaceae family Lepidobotryaceae family Oxalidaceae (including Averrhoaceae) family Geraniaceae family Dirachmaceae family Ledocarpaceae family Vivianiaceae family Biebersteiniaceae Other modern systems include those of Takhtajan (1987) with nine families, and Thorne (1992). Thorne's system was the same as Cronquist's except that Biebersteiniaceae, Dirachmaceae, Ledocarpaceae, and Vivianiaceae were reduced to subfamilies of Geraniaceae. Molecular phylogenetics: Angiosperm Phylogeny Group The elucidation of the relationships within the order by morphological or cytological methods alone had proven difficult as demonstrated by the widely different treatment by various authorities. For instance Cronquist and Thorne immersed the families Biebersteiniaceae, Dirachmaceae, Ledocarpaceae, Rhynchothecaceae and Vivianiaceae within Geraniaceae (Geraniaceae sensu lato), whereas Dahlgren and others maintained them as separate taxa, maintaining a "core" Geraniaceae (Geraniaceae sensu stricto). Price and Palmer (1993) were among the first investigators to apply molecular phylogenetics to this order, using the chloroplast gene rbcL. This disassembled the traditional morphologically defined grouping of dicotyledons, replacing it with a series of nested clades. The Geraniales segregated in the eudicot clade, specifically in the rosid subclade. The family circumscription of the Angiosperm Phylogeny Group (APG) of 1998 placed Geraniales Dumort. amongst the rosids with the following six families: Geraniales Dumort. 1829 Francoaceae A.Juss., 1832 Geraniaceae Juss., 1789 [ + Hypseocharitaceae Wedd., 1861] Greyiaceae Hutch., 1926 Ledocarpaceae Meyen, 1834 Melianthaceae Bercht. & J.Presl, 1820 Vivianiaceae Klotzsch, 1836 Hypseocharitaceae were a small family of eight species of the genus Hypseocharis found in the tropical mountainous regions of the Andes. The APG provided the option of considering them as a separate family or subsumed into Geraniaceae. By 2003, when the APG was published, it was apparent that the small families Francoaceae, Greyiaceae and Melianthaceae were closely related and were collapsed into one family as Melanthiaceae with Francoaceae as an optional synonym. Thus the number of families was reduced to four. The APG III classification (2009) was typical of newer arrangements. In this definition, Hypseocharitaceae was included within Geraniaceae, Francoaceae and Greyiaceae were included within Melianthaceae, and Ledocarpaceae was included within the Vivianiaceae. However, Considerable rearrangements took place in the 2016 APG IV system. Francoaceae was substituted for Melianthaceae, due to nomenclatural priority. The latter subsumed Vivianiaceae based on the work of Sytsma, Spalink & Berger (2014). However,