Introduction

The genus Ceruchus MacLeay, 1819 is currently classified in the tribe Ceruchini of the subfamily Syndesinae (Coleoptera: Lucanidae) (Smith 2006; Bouchard et al. 2011). However, the higher-level taxonomic placement of this genus has long been unstable and controversial. The earliest known species were originally described under the genus Lucanus Scopoli, 1763, until MacLeay (1819) established Ceruchus based on the type species Lucanus chrysomelinus Hochenwarth, 1785. The systematic placement of Ceruchus has changed considerably in previous classifications. Benesh (1960) considered the genus to belong to the subfamily Aesalinae MacLeay. However, Holloway (1960, 1968), based mainly on adult external morphology and male genitalia, reclassified Ceruchus and placed it together with Syndesus, Sinodendron, and Psilodon in Syndesinae. More recently, a molecular phylogenetic analysis further tested the monophyly of Syndesinae and the phylogenetic position of Ceruchini, revealing complex evolutionary relationships that partly challenge traditional morphology-based classifications and suggest that the placement of Ceruchini within Lucanidae remains incompletely resolved (Kim and Farrell 2015).

Earlier taxonomic knowledge of Ceruchus was derived mainly from European and North American species, with only a few early records from Asia (Benesh 1960). In recent decades, intensified collecting and taxonomic work in China and adjacent Sino-Himalayan regions has revealed a much richer and previously underdocumented diversity, with several species and new locality records reported from mountainous areas of southwestern and central China (Tanikado and Okuda 1994; Král 1995; Boucher and Král 1997; Okuda 2008; Huang et al. 2011; Huang and Chen 2013, 2017; Huang et al. 2020).

At present, 21 species are recognized in the genus, including 19 extant species and two fossil species, of which 12 have been recorded from China. During a recent examination of Chinese representatives of the genus, we discovered a new species from southwestern China. In this paper, we formally describe and illustrate the new species based on comparative morphology, increasing the number of Chinese species to 13 and the total number of species in the genus to 22. We also provide an updated identification key to the Chinese species of Ceruchus, prepared based on our examination of specimens and with reference to Huang and Chen (2017), summarize their distribution in China, and provide mitochondrial COI evidence supporting the separation of the new species from its sympatric close relative.