Background: <span style="background-color:inherit">Lucidotini is a diverse tribe of lampyrine fireflies present throughout the New World, Europe, and Asia. Most of the over 30 genera have overlapping diagnoses, largely due to a lack of revisionary and phylogenetic studies. Widespread convergence in sensory morphology, traditionally used in genus-level diagnoses, further compounds the taxonomic issues surrounding the Lucidotini. Recent work has cast light on the value of terminalia and genitalic traits for Lucidotini taxonomy and called for a more thorough screening of morphological characters. Of special interest are basal outgrowths of the phallus (</span><em style="background-color:inherit">i.e<span style="background-color:inherit">., ventrobasal processes)-currently only known in </span><em style="background-color:inherit">Alychnus<span style="background-color:inherit"> Kirsch and </span><em style="background-color:inherit">Photinus<span style="background-color:inherit"> Laporte-that can be quite informative at the species level, but its variation within Lucidotini remains poorly studied. Most Lucidotini species remain only superficially described, while internal characters-including those of terminalia and genitalia-which could inform species identification and phylogenetic relatedness, remain unknown. Upon studying eight Lucidotini species superficially looking like </span><em style="background-color:inherit">Photinus<span style="background-color:inherit"> and </span><em style="background-color:inherit">Photinoides<span style="background-color:inherit"> McDermott-all of which bearing long ventrobasal processes-we raised the hypothesis that they belonged to a genus yet to be recognized.</span> Methods: Here, we analyzed 97 morphological characters of 32 lampyrid species spanning 17 of 30 Lucidotini genera under Bayesian Inference. Results<span style="background-color:inherit">: </span><span style="background-color:inherit">We found evidence for the recognition and description of </span><em style="background-color:inherit">Saguassu<span style="background-color:inherit"> </span><strong style="background-color:inherit">gen. nov.<span style="background-color:inherit"> to include seven new species (</span><em style="background-color:inherit">Saguassu acutum<span style="background-color:inherit"> </span><strong style="background-color:inherit">sp. nov.,<span style="background-color:inherit"> </span><em style="background-color:inherit">Saguassu grossii<span style="background-color:inherit"> </span><strong style="background-color:inherit">sp. nov.,<span style="background-color:inherit"> </span><em style="background-color:inherit">Saguassu manauara<span style="background-color:inherit"> </span><strong style="background-color:inherit">sp. nov.,<span style="background-color:inherit"> </span><em style="background-color:inherit">Saguassu rebellum<span style="background-color:inherit"> </span><strong style="background-color:inherit">sp nov.,<span style="background-color:inherit"> </span><em style="background-color:inherit">Saguassu roura<span style="background-color:inherit"> </span><strong style="background-color:inherit">sp. nov.,<span style="background-color:inherit"> </span><em style="background-color:inherit">Saguassu serratum<span style="background-color:inherit"> </span><strong style="background-color:inherit">sp. nov. <span style="background-color:inherit"> and </span><em style="background-color:inherit">Saguassu sinuosum<span style="background-color:inherit"> </span><strong style="background-color:inherit">sp. nov.<span style="background-color:inherit">), in addition to </span><em style="background-color:inherit">Photinus dissidens<span style="background-color:inherit"> Olivier ((transferred herein, thus generating </span><em style="background-color:inherit">Saguassu dissidens<span style="background-color:inherit"> </span><strong style="background-color:inherit">comb. nov.<span style="background-color:inherit">), for which we also designate a lectotype and two paralectotypes). This previously neglected lineage of Lucidotini spans four South American biomes: Amazon, Atlantic Rainforest, Cerrado, and Pampa. Interestingly, </span><em style="background-color:inherit">Saguassu<span style="background-color:inherit"> species span a gradient of morphologies related to signaling: from </span><em style="background-color:inherit">Lampyris<span style="background-color:inherit">-style ventrally bulging eyes, tiny antennae and no lanterns; intermediate eyes and antennae, with complete lanterns as in </span><em style="background-color:inherit">Photinus<span style="background-color:inherit">; to small eyes and long antennae and small lanterns as in many </span><em style="background-color:inherit">Lucidota<span style="background-color:inherit"> Laporte. </span><em style="background-color:inherit">Saguassu<span style="background-color:inherit"> </span><strong style="background-color:inherit">gen. nov.<span style="background-color:inherit"> was consistently found closely related to the three other Lucidotini taxa with ventrobasal processes (</span><em style="background-color:inherit">i.e<span style="background-color:inherit">., </span><em style="background-color:inherit">Alychnus<span style="background-color:inherit">, </span><em style="background-color:inherit">Photinoides<span style="background-color:inherit">, and </span><em style="background-color:inherit">Photinus<span style="background-color:inherit">). We provide an occurrence map of and a dichotomous key to </span><em style="background-color:inherit">Saguassu<span style="background-color:inherit"> species, thoroughly compare this genus with co-occurring Lucidotini genera, and suggest steps towards a revision of the Lucidotini tribe.</span>
