The systematics of Philodromidae is far from complete, especially for the Neotropical genera. Among these, Petrichus Simon, 1886 is a poorly known genus restricted to arid and semi-arid environments of South America. In this work, we performed a total-evidence analysis to assess the phylogenetic relationships of Petrichus and revised the taxonomy. Petrichus is monophyletic and closer to Titanebo and the New World Ebo. Within Petrichus, two clades are obtained: the Eremean Clade, containing five species displaying a Neotropical distribution; and the Patagonian Clade, with the seven species inhabiting southern South America. Our results also support a previous hypothesis on the phylogenetic relationships within Philodromidae. Thanatini is monophyletic and includes Fageia and Berlandiella, although this is not statistically supported, whereas Philodromini emerges as paraphyletic. We propose Philodromini be expanded to contain all genera having eyes on tubercles analysed in this work plus the closely related Halodromus, whereas the circumscription of Thanatini should await future phylogenetic analyses with new evidence. As for taxonomic proposals, we synonymise Bacillocnemis Mello-Leitão, 1938 with Petrichus, Petrichus ornatus Schiapelli & Gerschman, 1942 and P. luteus (Nicolet, 1849) with P. junior (Nicolet, 1849), P. lancearius Simon, 1905 with P. tullgreni Simon, 1902; we transfer P. corticinus Mello-Leitão, 1944 to Misumenoides Pickard-Cambridge, 1900 (Thomisidae); and P. fuliginosus (Nicolet, 1849), P. cinereus Tullgren, 1901, P. sordidus Tullgren, 1901 and P. zonatus Tullgren, 1901 are regarded as nomina dubia. In total, 13 species are recognised for the genus, of which four are new (described by Griotti & Grismado): P. spira, from western Argentina, P. patagoniensis, from south-western Argentina, P. roigjunenti, from Argentina and Chile and P. eremicus, from north-central Chile.

ZooBank: http://zoobank.org/References/1220255e-6431-45c2-adfe-ed58d1f89b17