Plistonax

Silva Júnior, José O., Haseyama, Kirstern L. F. & Souza, Diego de S., 2021, Phylogenetic approach redefines Plistonax (Coleoptera, Cerambycidae, Lamiinae) with new combinations and a new genus of flat-faced long-horned beetles, Organisms Diversity & Evolution (New York, N. Y.) 21 (2), pp. 491-520 : 515-516

Synapomorphies of Plistonax

The presence of semierect seta in the elytral punctures (synapomorphy [27:1]) has been historically used by taxonomists to identify Plistonax ( Lacordaire 1872; Chemsak and Hovore 2002; Silva Júnior et al. 2019). Nevertheless, we have verified that similar setae (in shape or insertion) are present in the elytral punctures of species in Acanthoderini , such as Ozotroctes punctatissimus Bates, 1861 , and Punctozotroctes tuberculatus Galileo & Martins, 2011 , which differ from Plistonax by the last segment of the labial palpus expanded with no acuminate apex ( Tavakilian and Néouze 2007). P. tuberculatus also differs from Plistonax by having a very short gena. For this reason, it is important to verify not only the presence of this feature but also other characteristics important in the diagnosis of the genus. As a side note, P. bialbomaculatus does not have these setae and is the only exception known so far.

The deep apical invagination of the median lobe of the endophallus [36:2] may prove to be a reliable diagnostic feature for the genus, since it is not present in species of other genera included in our analyses. However, the terminalia of species of Acanthoderini have seldom been described, and although we examined the genitalia of only six species of Plistonax , we reinforce the utility of this character as a potential diagnostic feature for Plistonax , pending future data.

Concerning the homoplastic synapomorphies supporting the monophyly of Plistonax , the margin of gena curved in anterior view in males [1:0] is also found in the clade ( A. dejeani , E. leuconotus ). The other species examined by us have males with gena bearing a straight margin in anterior view [1:1]. This character was limited to males due to the sexual dimorphism in some species in the tribe (e.g., Steirastoma breve , Dryoctenes scrupulosus ), in which the females present a wider gena, possibly related to the habit of sawing wood before oviposition. The presence of tubercles on the mesoventral process [20:1] is not a reliable diagnostic feature due to the recurrent polymorphism (absent or present), here determined in two species ( P. albituberculatus and P. inopinatus ). Furthermore, these tubercles also occur in Acanthoderes , Aegomorphus , and Exalphus .

The clade ( P. albolinitus , P. inopinatus ) presented the best support values in the analyses and was the only clade of Plistonax with strong support in the Bayesian inference. It is supported by the following synapomorphies: males with black setae on the antennomeres IX–XI [11:1], presence of sparse white setae on the pronotum [18:1], and median-basal crest beyond middle of elytron [25:1]). The former also occurs in P. ariasi and in some species of Aegomorphus . The second synapomorphy is non-homoplastic, and as discussed previously, the presence of these setae in P. albolinitus was overlooked by Lane (1960) and Monné and Magno (1992). The last synapomorphy also occurs in other species of Plistonax and many other genera of the tribe ( Aegomorphus ; Ateralphus ; Dryoctenes Audinet-Serville, 1835 ; Miguelmonneus gen. nov.; and Steirastoma Lacordaire, 1830 ).

Other noticeable synapomorphies in Plistonax are the presence of tubercles on the inner surface of the antennomeres of males [4:1] and the shape of the semierect seta in the elytral punctures (thick or slender) [28:0 and 28:1, respectively]. The former supports the clade (( P. albolinitus , P. inopinatus ) ( P. senecauxi ( P. albituberculatus , P. hefferni , P. antonkozlovi ))), having a reversion in P. albituberculatus (state absent, [4:0]) and a missing data in P. hefferni . About the last synapomorphies mentioned, the state thick [28:0] supports the clade ( P. difficilis (( P. albolinitus , P. inopinatus ) ( P. senecauxi ( P. albituberculatus , P. hefferni , P. antonkozlovi )))), having a reversion to the state slender [28:1] in the clade ( P. albituberculatus , P. hefferni , P. antonkozlovi ). The slender seta also occurs in P. rafaeli and P. ariasi , thus postulated as the ancestral state of the character.