Abstract

Although the differentiation of clades at the species level is usually based on a justifiable and testable conceptual framework, the demarcation of supraspecific boundaries is less objective and often subject to differences of opinion. The increased availability of large-scale phylogenies has in part promulgated a practice of what we consider excessively splitting clades at the “genus” level. Many of these new genus-level splits are predicated on untenable supporting evidence (e.g., weakly supported phylogenies and purportedly “diagnostic” but actually variable, non-exclusive, or otherwise problematic opposing character state differences) without careful consideration of the effects on downstream applications. As case studies, we critically evaluate several recent examples of splitting established monophyletic genera in four amphibian families that resulted in the creation/elevation of 20 genus-level names (Dicroglossidae: Phrynoglossus, Oreobatrachus, Frethia split from Occidozyga; Microhylidae: Nanohyla split from Microhyla; Ranidae: Abavorana, Amnirana, Chalcorana, Humerana, Hydrophylax, Indosylvirana, Papurana, Pulchrana, Sylvirana split from Hylarana; Rhacophoridae: Tamixalus, Vampyrius, Leptomantis, Zhangixalus split from Rhacophorus, Rohanixalus split from Feihyla, Orixalus split from Gracixalus, and Taruga split from Polypedates), and also address the taxonomic status of the monotypic genus Pterorana relative to Hylarana. We reassess the original claims of diagnosability and justifications for splitting and argue that in many cases, the generic splitting of clades is not only unnecessary but also destabilizes amphibian taxonomy, leading to a host of downstream issues that affect categories of the user community (stakeholders such as taxonomists, conservationists, evolutionary biologists, biogeographers, museum curators, educators, and the lay public). As an alternative, we advocate for the use of the subgenus rank in some cases, which can be implemented to establish informative partitions for future research without compromising on information content, while avoiding gratuitous (and often transient) large-scale binomial (genus-species couplet) rearrangements. We encourage taxonomists to consider the actual needs and interests of the larger non-taxonomic end-user community who fund the majority of taxonomic research, and who require a system that remains reasonably stable and is relatively intuitive, without the need for inaccessible laboratory equipment or advanced technical scientific knowledge to identify amphibian species to the genus level.

Dicroglossidae, Microhylidae, Ranidae, Rhacophoridae, subgenus, synonym, taxonomic inflation

Taxonomic classifications are increasingly being informed by molecular phylogenies, both at the specific and supraspecific levels (e.g., Brown et al. 2015; Chan and Grismer 2019; Wood et al. 2020). Ideally, the Linnaean classification system should reflect the hierarchical structure of phylogenetic relationships, where nested, monophyletic units, inferred in robust phylogenetic analyses receive an assignment of Linnaean rank (genus, family, order, etc.). Because the species is the basic unit of classification and biodiversity, and the fundamental unit of evolution, delimiting clades at the species level can be based on a testable, biological, and conceptual framework (de Queiroz 2007; Sukumaran et al. 2021). In contrast, the demarcation of supraspecific boundaries is less objective and can be subject to interpretation and differences of opinion. Species-rich genera inherently contain higher levels of genetic structure, making them more amenable (and susceptible) to splitting (Malhotra and Thorpe 2004; Frost et al. 2006; Nicholson et al. 2012; Poe 2013; Poe et al. 2017). Consequently, the increasing availability of large-scale phylogenies encompassing deeper and broader taxonomic scales has facilitated the splitting of medium to large (and occasionally small) clades at the genus level into smaller subclades, each representing a separate genus (Mausfeld and Schmitz 2003; Malhotra and Thorpe 2004; Arnold et al. 2007; Hedges and Conn 2012; Nicholson et al. 2012). This clade-splitting exercise is becoming more prevalent in amphibian systematics (e.g., Frost et al. 2006; Biju et al. 2010, 2020; Oliver et al. 2015; Jiang et al. 2019; Dubois et al. 2021; Gorin et al. 2021), ostensibly to enhance taxonomic stability, usefulness, ease of management, and occasionally to create more regionally-circumscribed genus groups in the hope of improving conservation measures by developing local pride in biodiversity preservation. However, this practice is often predicated on untenable supporting evidence (e.g., weakly supported phylogenies, phylogenetic uncertainty, or ineffective and inaccurate “diagnostic” characters state comparisons; Oliver et al. 2015; Chandramouli et al. 2020; Dubois et al. 2021) without weighing the effects on downstream applications. When splits are supported solely on the basis of molecular data, they are more akin to a clade-naming exercise, rather than a practical and intelligible progression of taxonomic knowledge for the majority of end-users that require a genus name to apply to a phenotypic group that can be relatively easily distinguished from others, and thus aid in species identification. In fact, this practice of taxonomic inflation often confers little to no taxonomic value but instead, adds more confusion for the majority of end-users. As case studies, we investigate the supporting evidence used in several recent genus-level splitting examples from four families of amphibians [Dicroglossidae Anderson, 1871, Microhylidae Günther, 1858, Ranidae Batsch, 1796, and Rhacophoridae Hoffman, 1932] to highlight the undesirable confusion and instability created by the widespread genus-species binomial rearrangements resulting from this clade-spitting exercise.

Rhacophoridae is a large family containing more than 450 species that are mostly distributed across Asia with a disjunct occurrence in Africa (Frost 2024). The largest genus in this family is Rhacophorus Kuhl & van Hasselt, 1822 sensu lato, which comprises at least 99 species (Chan et al. 2018; Kropachev et al. 2022; Li et al. 2022; Brakels et al. 2023). Naturally, several large-scale phylogenetic studies revealed high levels of phylogenetic structure within this large genus (Li et al. 2008, 2009, 2013; Hertwig et al. 2013; Chan et al. 2018, 2020c). Rhacophorus sensu lato was subsequently split into several additional genera: Leptomantis Peters, 1867 (13 spp.) and Zhangixalus Li, Jiang, Ren & Jiang, 2019 (40 spp.) were recognized based on arguments reliant on phylogenetic structure and several putatively diagnostic morphological characters, distribution range, and reproductive mode (Jiang et al. 2019), while Tamixalus Dubois, Ohler & Pyron, 2021 and Vampyrius Dubois, Ohler & Pyron, 2021, were erected solely based on phylogenetic position—generic diagnoses were recapitulated from the published descriptions of type species without any reported examination of specimens (Dubois et al. 2021). Dubois et al. (2021) also split the relatively small genus Gracixalus Delorme et al., 2005 (19 species; Tran et al. 2023) creating Orixalus Dubois, Ohler & Pyron, 2021 based on the same criteria. Two other rhacophorid genera, Rohanixalus Biju et al., 2020 and Taruga Meegaskumbura et al., 2010, represent subclades of taxa previously assigned to the genus Feihyla Frost et al., 2006 and Polypedates Tschudi, 1838, respectively (Meegaskumbura et al. 2011; Biju et al. 2020). The genus Nanohyla Poyarkov, Gorin & Scherz, 2021 from the family Microhylidae is reciprocally monophyletic with the genus Microhyla Tschudi, 1838 and was split from it largely based on osteological characters, geographic distribution, and clade age (Gorin et al. 2021). In the family Dicroglossidae, the genus Phrynoglossus Peters, 1867 was recognized as distinct based on reciprocal monophyly with its sister genus Occidozyga Kuhl & van Hasselt, 1822 and other putative characters pertaining to morphology, ecology, and amplexus mode (Köhler et al. 2021). The genera Oreobatrachus Boulenger, 1896 and Frethia Dubois, Ohler & Pyron, 2021 were further split from Occidozyga solely based on inconclusive phylogenetic placements, without further supporting evidence (Dubois et al. 2021).

One of the most radical examples of wholesale supraspecific changes in amphibian taxonomy occurred in true frogs (family Ranidae) of the genus Hylarana Tschudi, 1838 sensu lato, which included the en bloc elevation of eight subgenera to the genus rank (Amnirana Dubois, 1992, Chalcorana Dubois, 1992, Humerana Dubois, 1992, Hydrophylax Fitzinger, 1843, Hylarana, Papurana Dubois, 1992, Pulchrana Dubois, 1992, Sylvirana Dubois, 1992) and the creation of two new genera (Abavorana Oliver, Prendini, Kraus & Raxworthy, 2015 and Indosylvirana Oliver, Prendini, Kraus & Raxworthy, 2015). This taxonomic upheaval was based on a weakly supported phylogeny, distribution ranges, and non-diagnostic (i.e., non-opposing, or non-discrete) morphological character comparisons (Oliver et al. 2015).

In this study, we review updated phylogenies from the latest studies or perform additional phylogenetic analysis using more comprehensive datasets, and evaluate the putatively diagnostic characters of the aforementioned newly-proposed genera (Rohanixalus, Taruga, Leptomantis, Zhangixalus, Tamixalus, Vampyrius, Orixalus [Rhacophoridae]; Nanohyla [Microhylidae]; Phrynoglossus, Frethia, Oreobatrachus [Dicroglossidae]; and Hylarana sensu lato [Ranidae]) to determine whether their recognition at the genus level is warranted. We also evaluate the status of Pterorana Kiyasetuo & Khare, 1986, which has repeatedly been demonstrated to be a member of Hylarana sensu lato in recent literature, but its status has not been resolved. We echo the recommendations of Vences et al. (2013) for a sensible, robust, and critical nomenclatural framework to guide practitioners, reviewers, and journal editors to consider before proposing, refuting, or supporting proposals, for splitting clades at the supraspecific level. We follow numerous other systematists, and advocate for the use of the subgenus rank (e.g., McCranie and Townsend 2008; Van et al. 2009; Brown et al. 2015; Mahony et al. 2017; Cox et al. 2018; Wood et al. 2020; Vogel et al. 2022) and/or informally-recognized taxonomic “groups” or “complexes” as convenient (e.g., Mahony et al. 2017; Flury et al. 2021; Grismer et al. 2021) for cases where subclades are phylogenetically supported but lack strong, unambiguously discrete, and opposing diagnostic characters based on comprehensive comparative studies of all (or at least most) known species. The subgenus rank can establish informative taxonomic partitions to facilitate research and conservation without compromising on information content, while simultaneously avoiding unnecessary and large-scale taxonomic disruptions to numerous formally named/long-established genus-species couplets (Smith and Chiszar 2006; Pauly et al. 2009; Vences et al. 2013; Cox et al. 2018), so, we embrace the practice of recognizing subgenera.

Our disagreement with the creation of the aforementioned new genera in no way undermines the research that was presented in the respective papers, as all have undeniably contributed to our knowledge of these (and/or other) taxonomic groups. The genera included in the case studies here were selected based on our own (admittedly subjective) familiarity with the taxa involved, and are in no way exhaustive or representative of the quality of the research presented therein. We are fully aware that there are many conflicting concepts and opinions held amongst members of the taxonomic community, on what should constitute a genus, how much support is needed, the type of characters and criteria that are sufficient to recognize a new genus-level split, whether the recognition of subgenera is an advisable or generally preferred practice, and whether taxonomists should even consider downstream effects for end users of binomials. We are also aware that there are differing opinions on what constitutes as “taxonomic progress.” The evolutionary relationships between species are not changing, but rather only our understanding of these relationships—as we gain more data and improved methods of analyzing them. We are of the opinion that the primary goal of taxonomy is to reflect, and eventually help us understand the true evolutionary tree, at which point we must achieve a stable taxonomy, at least at the genus level, where species will no longer be needlessly moved between genera. At this point, intra-generic taxonomic progress will continue with minimal impact to the binomial system, which is what everyone (not just taxonomists) uses as a system to communicate about biodiversity in general, and the species themselves. We have the utmost respect for our peers regardless of whether they share our opinions, and the expression of our opinions are in no way intended to create controversy or offense. We do not claim to offer any new approaches or concepts in this paper, but merely highlight what we consider to be a growing problem in Asian amphibian taxonomy and suggest options for how to reduce the impact of the problem.

In summary, in this paper, we offer our opinions on the negative impact of prematurely splitting genera based on inconclusive evidence such as incomplete taxon sampling (for morphological, molecular, biogeographical, and behavioral data), omission of relevant published data, and/or weakly supported phylogenies, which are often over-turned with the availability of larger datasets consisting of more extensive taxon and gene sampling (Chan et al. 2020a, 2020b; Chandramouli et al. 2020), or just a more comprehensive review of the available literature.

To facilitate consistent and objective assessments, we agree with and thus follow the Taxon Naming Criteria (TNC) framework proposed by Vences et al. (2013) to evaluate the criteria upon which the new genera were established. Of particular importance are the priority TNCs of Clade Stability and Phenotypic Diagnosability. The Clade Stability TNC refers to the stability of the monophyletic clade that is predicated on the strength of evidence for monophyly. Following Vences et al. (2013), strong evidence for monophyly should be based on (i) explicit phylogenetic analysis and independent analytical methods such as Maximum Likelihood and Bayesian Inference. Preferably, phylogenies should be consensual across a wider array of different analytical methods; phenetic methods such as Neighbor-joining are considered insufficient; (ii) robust clade support based on a relevant method that is explicitly justified (e.g., Hillis and Bull 1993; Goldman et al. 2000; Pauly et al. 2009; Hoang et al. 2017); (iii) dense taxon sampling to increase topological accuracy and taxonomic coverage to ensure that species can be reliably allocated to genera; and (iv) support by high-quality and independent datasets (e.g., from different genetic markers, such as both mitochondrial and nuclear genes that contain sufficient informative sites).

Because this study addresses supraspecific ranks, we employ the absolute diagnosability criterion for the Phenotypic Diagnosability TNC. This is the strictest form of the criterion that requires diagnostic characters to be shared by all species included in the genus and not found in any other species from closely related genera. We further add that characters detected in a small subset of representative taxa and assumed to be present in all other constituent species without evidence to support that assumption are deemed insufficient. Furthermore, the identification of proposed diagnostic characters must be based on a demonstrated thorough review of the pertinent literature (preferably supplemented with the examination of vouchered specimens). If authors disagree with the previous descriptions of published morphological characters, they must be discussed and corrected based on evidence, since overlooked published morphological variation is demonstrated herein to be a regular source of erroneous phenotypic definitions. We acknowledge that exceptions for certain characters and species can exist (defined as relative diagnosability by Vences et al. 2013) but this should necessarily be restricted to a small number of characters and minor representation of included species. In such cases, relative diagnosability should be clearly justified and accompanied by other sources of evidence (e.g., biogeography). The choice of characters included in the diagnosis should also be appropriate at the genus level. Following recommendations by Vences et al. (2013), diagnostic characters should be discrete, conspicuous, readily observable in live and preserved species of different sexes and life-history stages, and should not require overly specialized conditions, methods, skills, or equipment to observe (e.g., CT Scans). See Vences et al. (2013) for more detailed discussions on TNCs.

For the previously proposed genera Rohanixalus, Phrynoglossus, Frethia, and Oreobatrachus, we performed new phylogenetic analyses using more comprehensive datasets to determine whether the proposed genera are phylogenetically stable. We incorporated sequences of Rohanixalus from Biju et al. (2020) into the multilocus Sanger dataset by Chan et al. (2018) to determine whether the inclusion of additional Rohanixalus taxa could affect phylogenetic inference. We used Chan et al.’s (2018) dataset because it is larger (3483 bps [base pairs] vs. 1937 bps in length) compared to Biju et al.’s (2020) dataset and hence, should provide improved resolution. For Occidozyga, Phrynoglossus, Frethia, and Oreobatrachus, we collated 12S and 16S mitochondrial sequences from most recent studies (Chan et al. 2021, 2022b; Flury et al. 2021; Köhler et al. 2021; Trageser et al. 2021) resulting in a comprehensively sampled Occidozyga dataset (13 out of 18 described species). We used IQ-TREE 2 (Minh et al. 2020) to perform a maximum likelihood (ML) analysis (partitioned by gene) with model selection and 1000 bootstrap replicates. Sequences used in this study are listed in Table S1.

To determine the reliability of published morphological diagnoses purported to justify the division of Hylarana sensu lato and Microhyla sensu lato, we examined specimens (including type specimens whenever possible) or photographs of type specimens from the following museums: BMNH (British Museum of Natural History: now the NHMUK––Natural History Museum, London, UK); FMNH (Field Museum of Natural History, Chicago, Illinois, USA); JUHG (Jahangirnagar University Herpetological Group, Savar, Dhaka, Bangladesh); MCZ (Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts, USA); MNHN (Museum National d’Histoire Naturelle, Paris, France); ZSI/ERS (Zoological Survey of India, Eastern Regional Station, Shillong, Meghalaya, India); ZSI/K (Zoological Survey of India, Kolkata, West Bengal, India); LSUHC (La Sierra University Herpetological Collection, Riverside, California, USA); and ZRC (Zoological Reference Collection, Lee Kong Chian Natural History Museum, Singapore). The list of examined materials is provided in the Appendix. All measurements were made using digital calipers in millimeters rounded to the nearest 0.1 mm.

The taxonomic recommendations outlined in this study are based on the guiding principles that promote name stability and economy of change (Smith and Chiszar 2006; Vences et al. 2013; Cox et al. 2018). Because taxonomic nomenclature serves the primary function of name recognition—and because primary users are non-taxonomists—nomenclatural changes, especially at the supraspecific level should not only be predicated on robust, transparent, and reproducible evidence but should also serve a practical purpose. Therefore, the splitting of stable, long-established, and monophyletic genera should be based on clear and diagnosable traits that enhance taxonomic stability and the understanding of evolutionary history. We believe that splitting a stable and established genus should minimally be supported by (i) robust phylogenetic evidence, and be accompanied by (ii) evident diagnostic characters that enhance diagnosability for most end-users, carefully determined through both a comprehensive review of literature and preferably the direct examination of explicitly identified specimens, thus ensuring transparency and repeatability. Here we have shown that the establishment of the genera Rohanixalus, Vampyrius, Orixalus, Tamixalus (Rhacophoridae), Phrynoglossus, Frethia, and Oreobatrachus (Dicroglossidae) do not even meet the first minimal criterion and, hence, these genus-level names are herein considered synonyms. Other previously proposed genera such as Leptomantis, Zhangixalus, Taruga (Rhacophoridae), Nanohyla (Microhylidae), and some genera within Hylarana sensu lato meet the minimal criterion, but not the additional criterion of diagnosability, which causes more taxonomic uncertainty (Fig. 2) as opposed to enhancing stability (Chan et al. 2020a). However, we recognize that the partitioning and recognition of these clades could potentially facilitate future research and, hence, we consider the use of the subgenus rank to be an ideal compromise because it provides a formal rank with which to discuss intrageneric clades for the portion of scientists who would use them without requiring large-scale genus level rearrangements of species (Brown et al. 2015; Mahony et al. 2017; Wood et al. 2020).

Although molecular phylogenetics can be leveraged to enhance taxonomic clarity, the misuse and misinterpretation of phylogenetic trees has repeatedly instigated the reverse engineering of characters to match the arbitrary partitioning of clades. This can lead to undiagnostic or lengthy combinations of characters that are coerced to fit the pre-conceived conception of a phylogenetically-derived taxonomic rank (Oliver et al. 2015; Dubois et al. 2021). In this study, we argue that carving up clades at the genus level and finding discriminating patterns where none exist (taxonomic pareidolia) destabilizes instead of enhances taxonomy. Inaccurate diagnoses of genera can lead to incorrect interpretations of morphological evolution, or can have cascading ramifications in other fields such as biogeography and comparative phylogenetic studies. For example, improper characterization of distribution ranges, e.g., in Nanohyla (Gorin et al. 2021) and Zhangixalus (Jiang et al. 2019), can potentially lead to erroneous inferences of ancestral ranges, distribution/niche modelling, and biogeographic interpretations.

We accept that taxonomy in amphibians has relied heavily on internal morphology to diagnose amphibian genera (e.g., Parker [1934] for microhylids; Boulenger [1920] for ranids). Historically (in the 1800 to mid 1900s), taxonomists catered primarily to the very small community of academics and naturalists. Systematic rearrangements had little effect on the non-taxonomic community due to a lack of access to taxonomic publications and a limited use for the binomial system when subjects such as conservation, ecology, biogeography, phylogenetics, herpetoculture (pet trade), etc., were non-existent or barely in their infancy. Furthermore, classical taxonomists had only a negligibly small sample size of the currently known diversity to study, and even today, few if any taxonomic groups (at least in Asian amphibians) have been comprehensively reviewed with the goal of determining whether the historically purported diagnostic internal morphological characters have withstood the test of time. Although we applaud the extensive efforts of taxonomists who have made large strides in the field on some groups (e.g., Meegaskumbura et al. 2010; Gorin et al. 2021) and we fully agree that the study of internal morphology is incredibly valuable for our understanding of amphibian evolution, the end user community of binomials is now far larger than the taxonomic community. It has not escaped our attention that splitting established monophyletic genera entirely or primarily based on internal morphology is not a justifiable disruption to that much larger community who may view such actions as unnecessary or even scientific elitism.

Recently, several studies have invoked phylogenetic uncertainty as justification to form new genera as a means to stabilize taxonomy (Biju et al. 2020; Chandramouli et al. 2020; Gorin et al. 2021), while others carve up large, weakly supported phylogenies without providing diagnostic characters (Dubois et al. 2021). We oppose both practices and argue that creating new genera in the light of insufficient data, uninformative data, or weakly supported phylogenetic relationships destabilizes taxonomy by creating cascading and compounding taxonomic problems. Uncritical splitting can create paraphyly, which requires the creation of more genera to resolve (taxonomic inflation), resulting in increasingly small or monotypic genera. This was exemplified by the elevation of eight subgenera in Hylarana to the genus rank, resulting in several paraphyletic clades that necessitated the creation of more genera to obtain monophyly—Abavorana (two spp.) and Indosylvirana (uncertain membership; Oliver et al. 2015). Similarly, in the family Rhacophoridae, the recognition of Leptomantis at the genus-level resulting in the paraphyly of Rhacophorus sensu lato, and thereby necessitating the creation of Zhangixalus to obtain monophyly. Unresolved phylogenies that are based on poor taxonomic coverage at the species level can create genera with uncertain membership, leading to frequent changes in generic names of species. For example, genomic data (Chan et al. 2020b) revealed that Indosylvirana nicobariensis was incorrectly placed in the African genus Amnirana by Oliver et al. (2015). Subsequently, the monotypic genus Bijurana Chandramouli, Hamidy & Amarasinghe, 2020 was proposed to accommodate this taxon based on the illogical justification of uncertain phylogenetic relationships (Chandramouli et al. 2020), and then, subsequently, was synonymized with Indosylvirana due to the lack of supporting evidence (Chan et al. 2020a). Injudicious splitting has caused this taxon to switch genus no less than five times in the last 17 years (Frost et al. 2006; Frost 2024), which we consider to be an outcome typifying extreme taxonomic instability. Similarly, numerous poorly defined and unresolved clades within Hylarana sensu lato have caused more than 20 taxa to be repeatedly transferred among the genera Amnirana, Sylvirana, Indosylvirana, Hydrophylax, Papurana, and Chalcorana (Frost 2024). Several other species were regarded as incertae sedis because they were not included in the study by Oliver et al. (2015) (Frost 2024). This confusion is compounded by the lack of diagnostic characters of the proposed genera, making it impossible to reliably assign species to genera for which no corresponding molecular data are available. Ironically, Dubois et al. (2021) opposed the splitting of Hylarana by Oliver et al. (2015) on the basis of poor branch support in their phylogeny, only to commit the same transgression by proposing numerous new genera based on their own poorly supported phylogeny (e.g., Frethia, Tamixalus, and Vampyrius). Instead of facilitating a better systematic understanding of their respective groups, these unwarranted nomenclatural acts have created more confusion and misunderstanding, all of which could have been avoided by applying a more robust, sensible, and critical framework for taxonomic partitioning—or, simply, by not proposing taxonomic rearrangements at all (Wiens 2007; Spinks et al. 2009, 2014; Poe 2013; Langer et al. 2017; Parker 2018). Therefore, we outline a simple, sensible, and effective framework based on the TNCs of Vences et al. (2013) to guide nomenclatural practice and the splitting of clades at the genus level (Fig. 4).

Figure 4. 

A suggested guide for sensible nomenclatural practice at the genus level based on Taxon Naming Criteria (TNC) sensu Vences et al. (2013).

The downstream effects of widespread genus-level rearrangements for the end-user have rarely been a strong consideration for the proposed splitting of monophyletic genera. Proposed end-user benefits of splitting large genera, if mentioned at all, have included reasons like large genera being difficult to manage, which we find to be an illogical argument (see Manageability Accessory TNC in Vences et al. 2013; Hedges and Conn 2012; Nicholson et al. 2012). Due to a lack of expertise (Smith and Chiszar 2006) or data to refute proposed splits, the vast majority of the end-user community typically offers little or no resistance and blindly follows taxonomic changes, resulting in rapid, unquestioned normalization and perceived “acceptance” due to the volume of usage of the newly proposed combinations (Pauly et al. 2009; but also see counter argument by Frost et al. 2009; Wüster and Bérnils 2011). Splitting genera and creating large-scale rearrangements of species create an illusion of importance, quality of work, or progression in the field. The immortalization and sense of prestige from creating new taxonomic names for some are strong incentives for proposing large scale rearrangements (Borrell 2007; Kaiser et al. 2013; Wüster et al. 2021). The perception that papers proposing largescale rearrangements rapidly accumulate citations could also incentivize such actions by improving researchers’ nomenclatural acts, bibliometrics, potential employment opportunities, promotions, access to funding, higher impact journals, and general appearance of scientific merit. Most large museum collections worldwide no longer attempt to keep up with the systematic fluctuations, resorting to outdated taxonomic arrangements while awaiting stability that will not be obtained without a widespread change in current attitudes towards genus-level splitting. Museum collections arranged using outdated taxonomies directly hinder scientific progress in all fields that rely on such collections, including and especially taxonomy. The practice of unnecessary splitting at the genus level, therefore, is usually (/almost always) far more beneficial for the authors of the papers that propose the splits than for the vast majority of the scientific and non-scientific community of end-users who feel obliged to follow such proposals and are forced to tolerate the ensuing instability, confusion, and chaos.

It may be argued that online taxonomic databases can somehow negate the need for a stabilized taxonomy as frequent changes can be logged and curated as they are proposed. However, databases on large taxonomic groups (e.g., Amphibian Species of the World [Frost 2024]; AmphibiaWeb [AmphibiaWeb 2024]), though invaluable, are subject to their own unique issues, e.g., errors in synonymies, intentional/unintentional omissions of taxonomic changes due to simply missing a paper, misinterpretation of published data, or subjective decisions by database curators to reject published proposals for taxonomic rearrangements (Frost et al. 2009; Liedtke 2019; Dubois et al. 2021; Dubois 2022; Dufresnes et al. 2022; Mahony and Kamei 2022; Frost 09 July 2020, https://amphibiansoftheworld.amnh.org/Curator-s-blog). Despite this, non-taxonomists and even taxonomists without extensive expertise on the literature of a particular group can easily misinterpret information on such databases (e.g., unintentional publication of many new genus-species combinations in Hylarana as mentioned above). Users often also wrongly assume recently proposed systematic rearrangements that are reflected on major databases are stable and widely accepted (Wüster and Bérnils 2011). For example, Phrynoderma Fitzinger, 1843, split from Euphlyctis Fitzinger, 1843 by Dubois et al. (2021), was subsequently updated on Frost (2024, in 2021), and is now reflected on the official revised Indian Wild Life (Protection) Amendment Bill 2022 where four species are listed as Phrynoderma under the Schedule II category, the second highest national protection level (Anonymous 2022). Dufresnes et al. (2022) subsequently rejected the genus level recognition of Phrynoderma, due to a lack of diagnosability and necessity, and instability due to the absence of a taxonomic revision of the type series of the type species for both Phrynoderma and Euphlyctis. Three additional species are listed in Schedule II in the genera Zhangixalus, Sylvirana and Hydrophylax (Anonymous 2022), herein proposed to be treated as subgenera. Besides an immediately outdated taxonomy in an infrequently revised government legislation for the protection of species considered vulnerable to national level extinction, the segregation of species into undiagnosable genera and appearance of these same species in literature and on databases with different genus-species combinations to those on the legislation will lead to unnecessary confusion for those responsible for the enforcement of laws related to the protection of these species. This will have a direct negative impact on conservation efforts. Online taxonomic databases can certainly not be held responsible for how users interpret (or misinterpret) the reliability of presented binomial arrangements when the aim of such databases is usually to try to objectively reflect changes proposed in the cited taxonomic literature. In cases where multiple taxonomies are simultaneously reflected in the literature, expecting databases to able to select the most popular/prevalent taxonomy at any single point in time is unreasonable, especially when preferences for one taxonomy over another can be regional, or even political. Therefore, blindly following the taxonomy displayed in databases, without demonstrably referring directly to the relevant cited literature, should be avoided at least in scientific writing or when preparing important legislation.

Although we have focused on a few recent examples where we demonstrate that the splitting of genera was arguably unnecessary, many other similar examples certainly require further investigation using the same or similar criteria and justifications outlined herein. However, we emphasize that nomenclatural stability and end-user consideration should be prioritized since the unnecessary synonymization of genera is as destabilizing as unnecessarily splitting them. For this reason alone, some originally poorly justified generic splits are probably now best maintained. As an example, phylogenetic analyses in Biju et al. (2010) demonstrated that the mainly South Asian genus Pseudophilautus comprised two clades. Biju et al. (2010) created the genus Raorchestes to apply to one of the clades, diagnosing the “genus” simply as the clade that did not include the type species of Pseudophilautus (they called their taxa inclusion/exclusion through phylogenetic framework an “Entexognosis”). The authors defined the group through “brief characterization of characters” (they called an “Idiognosis”) listing non-diagnostic morphological characters, the general distribution, and reproductive mode, without comparison to related taxa. Although this action fitted no obvious practical purpose beyond splitting a monophyletic Pseudophilautus into two biologically and morphologically indistinguishable genera, its recognition was widely and blindly followed by biologists. At that time, the genus Pseudophilautus had only recently been elevated from synonymy (Li et al. 2009), so most of the historically named Raorchestes taxa spent little time in the genus Pseudophilautus sensu lato. Since its inception, at least 35 new species have been described in the genus Raorchestes comprising almost half the currently recognized taxa. As a result, despite not fulfilling most of the criteria for recognition discussed herein, we would not suggest now synonymizing the genus Raorchestes with Pseudophilautus as it would require the creation of a large number of new genus-species name combinations that would lead to largescale instability.

We duly acknowledge the existence of distinct subclades within the genera Rhacophorus, Feihyla, Polypedates, Gracixalus, Microhyla, Occidozyga, and Hylarana. However, we reject the need for those clades to be recognized as separate genera because they are not predicated on strong evidence of clade stability and/or phenotypic diagnosability. We demonstrate that the premature recognition of poorly supported and undiagnosable subclades as distinct genera promotes taxonomic instability and compounding downstream issues, especially given that genus, in Linnaean rank, is arguably the most prominent supraspecific rank (and of high public profile) for communication amongst biologists, and between biologists and the general public (Smith and Chiszar 2006; Vences et al. 2013). We request that authors refrain from suggesting any changes without clearly providing strongly supported phylogenetic justification, operationally functional diagnoses, explicitly addressing TNCs, and, finally, clearly demonstrating how the vast majority of end-users (i.e., non-taxonomic community) will benefit from the subdivision of a well-established genus and subsequent taxonomic rearrangements that result from its recognition. We emphasize that the latter must be predicated on information content. Editors and reviewers are also asked to consider the mostly unavailable resources and huge expense that museums and databases globally must bear to update the taxonomy of their collections, occasionally simply to gratify the whims of authors intent on splitting monophyletic genera, when assessing the merits and making recommendations to publish such papers (Kaiser et al. 2013). Finally, the scientific community is asked to question the quality of work/data, the need, and the value of all proposed taxonomic changes. We believe that justified pushback from both amateur and professional taxonomists is the best safeguard against disruptive taxonomy, which create large-scale taxonomic upheavals, often for the sake of change itself. Most research in our field is essentially publicly funded, so modern taxonomists have a responsibility to the public to ensure that their actions serve the needs of the broader end-user community.

For access to specimen collections and support during museum visits, SM thanks Kaushik Deuti and K. Venkataraman, and the staff of the amphibian sections (ZSI, Kolkata), Md. Kamrul Hasan and Md. Mofizul Kabir and former students Mushfiq Ahmed and Md Kamal Hossain (JUHG, Savar), Alan Resetar (FMNH, Chicago) and Barry Clark and Jeffrey Streicher (NHMUK, London). This research was supported by the following funding: Field Museum of Natural History Science Visiting Scholarship to SM; NSF DEB 1654388, 1557053, and 0743491 to RMB. We thank George Zug, Bryan Stuart and Frank Glaw for their thoughtful reviews of our submitted paper.

Specimens examined.

Hylarana (Humerana) humeralis (Boulenger, 1887): MYANMAR • 2 females, adult, paralectotypes of Rana humeralis; “Teinzo, Upper Burma”; BMNH 1947.2.2.33 (ex. BMNH [18]89.3.25.45), FMNH 9795 • 1 male, adult; “Upper portion of Pegu River, east of Pegu Yomas, Burma”; ZSI/K 17240.

H. (Hum.) lateralis (Boulenger, 1887): MYANMAR • 1 female, adult; “Moulmien, lower Burma”; ZSI/K 2758.

Hylarana (Hydrophylax) cf. bahuvistara (Padhye et al., 2015): INDIA • 1 male, adult; “Orissa, Badrama, Sambalur Dist”; ZSI/K NOA5 • 2, adults unsexed, paralectotypes of Rana malabarica; “Bengale”; *MNHN-RA-0.4439, 1989.3348.

H. (Hyd.) gracilis (Gravenhorst, 1829): SRI LANKA • 1 male, adult, holotype of Lymnodytes macularius Blyth, 1855; “Ceylon”; ZSI/K 10037.

H. (Hyd.) leptoglossa: MYANMAR • 3, unsexed, syntypes of Hylorana leptoglossa; “near Rangoon, Burmah”; *MCZ A1588, 125024, 125025 • 1 female, adult, syntype of Hylorana granulosa Anderson, 1871; “Pegu”; ZSI/K 4009. – INDIA • 1 female, adult, syntype of Hylorana granulosa; “Seebsaugar, Assam”; ZSI/K 2790 • 3, subadults unsexed; “stn. 14, Patichhani, S. Tripura”; ZSI/K A8123 (3 specimens) • 1, subadult unsexed; “stn. 5, Sepahijala Bio Complex, e. of Agartala, Tripura”; ZSI/K A8116. – BANGLADESH • 1 male, 1 female, adult; “Kaptai”; JUHG 0109, 0107.

H. (Hyd.) malabarica: INDIA • 1 female, adult, lectotype; “Malabar”; *MNHN-RA-0.4440 • 2 adult unsexed, paralectotypes of Rana malabarica; “Cote de Malabar”; *MNHN-RA-1989.3351, 1989.3352.

H. (Indosylvirana) aurantiaca Boulenger, 1904: INDIA • 1 female, adult, holotype of Rana aurantiaca; “Trivandrum, Travancore”; BMNH 1947.2.2.92 (ex. BMNH 1903.9.26.1).

H. (I.) flavescens (Jerdon, 1853): INDIA • 1 male, adult, “syntype” fide Chanda et al. 2001 (type status indirectly rejected by Biju et al. 2014); “S. India” [Coonoor, Nilgiris]; ZSI/K 4301.

H. (I.) montana (Rao, 1922): INDIA • 1 female adult, lectotype of Rana gracilis var. montanus; “Mysore”; BMNH 1947.2.2.66 (ex. BMNH 1921.1.20.6) • 1 female adult, paralectotype of Rana gracilis var. montanus; “Mysore”; BMNH 1947.2.29.43 (ex. BMNH 1921.1.20.7) • 1 female, juvenile, holotype of Rana bhagmandlensis Rao, 1922; “Bhagmandola R., Coorg”; BMNH 1947.2.2.12 (ex. BMNH 1921.1.20.1).

H. (I.) temporalis: SRI LANKA • 1 female, adult, lectotype of Hylorana temporalis; “Ceylon”; ^BMNH 1947.2.3.5 (ex. BMNH [18]53.7.9.11) • 1 female, adult, paralectotype of Hylorana temporalis; “Ceylon”; BMNH 1947.2.29.46 (ex. BMNH [18]58.10.15.5) • 2 males, adult, paralectotype of Hylorana temporalis; “Ceylon”; BMNH 1947.2.2.6 (ex. BMNH [18]58.10.15), 1947.2.29.47 (ex. BMNH [18]58.10.15.6) • 3 juveniles, unsexed, paralectotype of Hylorana temporalis; “Ceylon”; BMNH 1947.2.2.7 (ex. BMNH [18]58.10.18), 1947.2.29.44 (ex. BMNH [18]52.2.19.43), 1947.2.29.45 (ex. BMNH [18]52.2.19.44).

H. (“Indosylvirana”) nicobariensis: INDIA • 1 male, adult, syntype of Hylorana nicobariensis; “Nicobar” [Nicobar Is.]; ZSI/K 3362 • 1 male, adult; “Kopen Heat, Galathea, Great Nicobars”; ZSI/K A9137.

H. (Sylvirana) cf. annamitica (Sheridan & Stuart, 2018): VIETNAM • 1 male, 1 female, adults; “Mau-Son Mts, 3000–4000ft., Tonkin, Kwango Frontier”; BMNH 1903.4.29.50, 1903.4.29.47.

H. (S.) danieli: INDIA • 1 female, adult, holotype of Rana danieli; “Mawphlang forest (Alt. 1535 m), Khasi Hills” [Meghalaya State]; ZSI/K A6966 (ex. ZSI/V/ERS 804) • 1 unsexed, paratype of Rana danieli; “Mawphlang forest (Alt. 1535 m), Khasi Hills” [Meghalaya State]; ZSI 6967 (ex. ZSI/V/ERS 818) • 1 female, adult, paratype of Rana danieli; “Nongkrem (Alt. 1520 m), Shillong, Khasi Hills” [Meghalaya State]; ZSI 6968 (ex. ZSI/V/ERS 805).

H. (S.) faber: CAMBODIA • 1 male, adult, holotype of Rana (Sylvirana) faber; “Phnom Aural Wildlife Sanctuary, Kampong Speu Province Southwest Cambodia (UTM 1328200N 0307700E)”; *MNHN RA 2001.0261.

H. (S.) garoensis: INDIA • 1 juvenile unsexed, syntype of Rana garoensis; “Garo hills, Assam, above Tura, at an altitude of 3500 to 3900 feet.” [Meghalaya State]; ZSI/K 18557.

H. (S.) guentheri (Boulenger, 1882): CHINA • 2 females, adults, syntypes of Rana guentheri; “Amoy” [Fujian]; BMNH (18)76.3.14.1, (18)76.3.14.2.

H. (S.) khare comb. nov.: INDIA • 1 male, adult, holotype of Pterorana khare; “Sanuoru river, Kohima, Nagaland (alt. 1440 m a. s. l.)”; ZSI/K A9095 (ex. ZSI/V/ERS 8214) • 1 male, adult, paratype of Pterorana khare; “Rukhroma river, Kohima, Nagaland (alt. 1400 m a. s. l.)”; ZSI/K A9097 (ex. ZSI/V/ERS 8215).

^^H. (S.) lacrima: BANGLADESH • 2 females, adults; “Kaptai village, Kaptai, Rangamati, Chittagong Div., Bangladesh”; JUHG 0006, JUHG 0104 • 1 male, adult; “Kaptai village, Kaptai, Rangamati, Chittagong Div., Bangladesh”; JUHG 0071 • 2 females, adults; “Bandarban, Chittagong Div., Bangladesh”; JUHG 0191, 0192 • 3 males, adults; “Bandarban, Chittagong Div., Bangladesh”; JUHG 0174 to 0176.

H. (S.) latouchii (Boulenger, 1899): CHINA • 1 male, 1 female, adults, syntypes of Rana latouchii; “Kuatun, N.W. Fokien”; BMNH 1947.2.1.81 (ex. BMNH [18]98.9.15.4), 1947.2.1.83 (ex. BMNH [18]99.4.24.71).

H. (S.) maosonensis Bourret, 1937: VIETNAM • 1 male, adult, lectotype of Hylarana maosonensis; “Mau Son, Lang Son Province, Vietnam”; *MNHN RA 1938.50.

H. (S.) mortenseni (Boulenger, 1903): THAILAND • 1 female, adult, topotype; “Koh Chang Is., Siam” [Thailand] BMNH 1921.2.12.1.

H. (S.) nigrovittata: MYANMAR • 1 male, 1 female, adult, paralectotypes of Lymnodytes nigrovittatus; “Mergui”; ZSI/K 2685, 2773 • 1 female, adult, lectotype of Lymnodytes nigrovittatus; “Mergui”; BMNH 1947.2.2.99 (ex. [18]93.2.14.4) • 1 female, adult; “Nyaungbin, a village at the north end of Indawgyi Lake, Myitkyina Dist., Upper Burma”; BMNH 1929.12.1.2.

H. (S.) cf. nigrovittata: THAILAND • 1 male, adult; “Pran River, P. Siam”; BMNH 1931.1.14.1.

H. (S.) spinulosa (Smith, 1923): CHINA • 1 female, adult, paratype of Rana (Hylarana) spinulosa; “Tun Fao, Kachek R., Hainan, 400ft.”; *MCZ A9427 (ex. field number 6886).

Microhyla (N.) annectens Boulenger, 1900: MALAYSIA • 1 female, adult; “Parit Falls, Cameron Highlands, Pahang”; LSUHC 10926, • 1 female, adult; “Brinchang Swamp, Cameron Highlands, Pahang”; LSUHC 7219.

M. (N.) annamensis: VIETNAM • 1 female, adult; “Suoi Mo, Sung Thuy Loan Basin, Danang Province”; ZRC 1.11841.

M. (M.) borneensis Parker, 1928: MALAYSIA • 1 female, adult; “Kubah National Park, Sarawak”; ZRC 1.11915.

M. (M.) mantheyi Das, Yaakob & Sukumaran, 2007: MALAYSIA • 1 female, adult; “Engkabang Trail, FRIM, Kepong, Selangor”; ZRC 1.10177.

Notes:

^Biju et al. (2014: 320) designated “NHM 1947.2.2.5” as the lectotype. They then identified that there was confusion regarding the current and original number in the “Comments” section and treated “1947.2.3.5” as the correct number. In the caption for figures 17d–f and 18d–f they stated the specimen number as “lectotype of Hylorana temporalis (NHM 1947.2.3.5 [ex BMNH 53.7.19.11]):…”, using one of the dubious original numbers. We here resolve the conflicting information found between different sources regarding the specimen numbers of the lectotype. On the specimen jar, the current and original specimen numbers are given as “1947.2.2.5” and “53.7.9.11”, respectively; in the BMNH Accession Register they are given as “1947.2.3.5” and “53.7.9.11”, respectively, the BMNH Specimen Catalogue gives only the original number as BMNH “53.7.19.11” and the specimen tag gives the number “1947.2.3.5”. We only regard the combination of numbers (both current and original) given in the BMNH Accession Register as the correct numbers for the lectotype of Hylorana temporalis Günther, 1864.

^^These specimens have previously been reported as “Hylarana cf. nigrovittata” by Mahony et al. (2009). The specimens correspond morphologically with the original description of H. (S.) lacrima and populations from nearby Mizoram State, India have subsequently been confirmed molecularly to represent this species (e.g., Lalronunga et al. 2021). This represents the first confirmed country record of Hylarana (S.) lacrima from Bangladesh.

*photos of museum specimens only.