Integrative Taxonomic Approach Research Articles

A redescription and new generic placement of the New Zealand marine-associated jumping spider Marpissa marina (Goyen, 1892) (Araneae: Salticidae: Euophryini)

ABSTRACT The jumping spider Marpissa marina (Goyen, 1892) is endemic to Aotearoa New Zealand. In this paper, we redescribe the species. Marpissa marina was placed in the Northern Hemisphere genus Marpissa due to its subjective similarity to spiders in that genus. The original description lacked modern morphological diagnoses and useful illustrations. The description was based largely on the female, and therefore lacked the taxonomically important characters seen in the male pedipalp. Previous literature has suggested M. marina may be related to the Australian genus, Maratus Karsch, 1878. We applied an integrative taxonomic approach based on diagnostic morphological characters and molecular analysis for a more detailed species description and assignment into an appropriate genus. Morphological features indicate that M. marina belongs to Maratus. This is supported by phylogenetic analyses using DNA sequences from the nuclear gene Actin 5C and the mitochondrial gene 16S ribosomal RNA. We transfer Marpissa marina into the genus Maratus, as Maratus marinus (Goyen, 1892), new combination.

A master in disguise? The rediscovery of Misumena bicolor Simon, 1875 (Araneae: Thomisidae)

Misumena bicolor Simon, 1875, an enigmatic species known only from the male holotype collected on Corsica (France), has remained elusive since its initial description. In this study, we report new occurrences of M. bicolor from Sardinia (Italy) and Bavaria (Germany) based on male material, considerably expanding its known distribution. Employing an integrative taxonomic approach encompassing both morphological and COI (barcode) analyses, we confirm M. bicolor as a valid species. As the male of M. bicolor apparently has a distinct coloration, we complement the known distributional data with possible sightings of photographic observations from various naturalist portals and hereby provide additional evidence for the establishment of the species on the French mainland and in Germany.

Rickettsia rickettsii subsp. californica subsp. nov., the etiologic agent of Pacific Coast tick fever.

The etiologic agent of Pacific Coast tick fever (PCTF), a moderately severe tickborne illness that resembles Rocky Mountain spotted fever (RMSF), was first isolated in 1966 from specimens of Dermacentor occidentalis (the Pacific Coast tick) obtained in California. For several decades, this bacterium was identified ambiguously as the unclassified spotted fever group Rickettsia species 364-D, Rickettsia 364, or Rickettsia philipii. However, none of these epithets satisfied criteria of formal bacterial nomenclature. Data developed from mouse serotyping studies performed 45 years ago, and multi-locus sequence typing several decades later, indicated that this bacterium was similar to, but distinct from isolates of Rickettsia rickettsii, the etiological agent of RMSF. We applied an integrative taxonomic approach, combining phenotypic, ecological, and clinical data with whole genome sequencing of 11 contemporary isolates of this pathogen to identify it as a distinct subspecies of R. rickettsii, and propose the name Rickettsia rickettsii subsp. californica subsp. nov.

Phylogeny and systematics of the colubrid snake genera Liopeltis and Gongylosoma (Squamata: Colubridae) and description of a new Himalayan endemic genus and species.

The colubrid snakes of the genera Gongylosoma Fitzinger, 1843 and Liopeltis Fitzinger, 1843 are distributed across south and southeast Asia with five and eight nominate species, respectively. Despite their wide distribution, members of these genera are among some of the least-known colubrids. The two genera were considered synonymous in the past only to be separated later, and are defined on rather nebulose characters with a lack of support from molecular data. To test the monophyly of the two genera, we generated molecular data for the type species of Gongylosoma and species representing the two genera, including samples of Liopeltis rappii (Günther, 1860) from the western Himalayas. Results recovered paraphyly of Liopeltis, especially with regard to the genus Gongylosoma. Morphological data supports recognizing the western and eastern populations of L. rappii as two distinct species. The findings from our integrative taxonomic approach advocate establishing a new genus to embody Liopeltis rappii and a new allied species from the central and western Himalayas. A rediagnosis and revised classification of the genera Gongylosoma and Liopeltis is presented. The results further hint at cryptic diversity across members of the two genera, warranting scrutiny of the most widespread members of the group.

A new species of the pill millipede genus Rhopalomeris Verhoeff, 1906 (Diplopoda, Glomerida, Glomeridae) from Myanmar, and notes on Rhopalomeriscarnifex (Pocock, 1889).

The taxonomy of the pill millipede genus Rhopalomeris Verhoeff, 1906, which is restricted to Indochina and currently comprises six described species, is refined and updated. An integrative taxonomic approach was employed that combines morphological examination with DNA barcoding using the cytochrome c oxidase subunit I (COI) gene for species identification and delineation. The first objective was to confirm the identity of Rhopalomeriscarnifex (Pocock, 1889), a charismatic species known as the "candy pill millipede" due to its vivid coloration, based on specimens collected near the type locality in Myanmar. The second objective was to describe a new species, Rhopalomerisnigroflava Likhitrakarn, sp. nov., discovered in Linno Gu, Kayin State, Myanmar. This new species is distinguished by its small body size (5.1-9.7 mm long) and yellow body with contrasting brown to blackish markings on certain terga. In addition, the position of the telopod syncoxital lobe relative to the lateral syncoxite horns separates it from other Rhopalomeris species. The interspecific divergence between R.nigroflava Likhitrakarn, sp. nov. and other congeners ranges from 10.85% to 16.13%, based on uncorrected COI p-distances, while the intraspecific divergence was 0%-7.44%. A distribution map of and a revised identification key to all known species of Rhopalomeris are also provided.

Integrative taxonomy of Teucriogethes pollen beetles (Coleoptera: Nitidulidae: Meligethinae), with implications on the systematics of the genus Teucrium (Lamiaceae).

In highly specialised phytophagous insects, important insights on phylogeny of the involved insect group can be often inferred from the evolutionary history of their host plants, and vice-versa, as in the case for a new, peculiar species of pollen beetles, recently discovered in Central China (Hubei Province). This new species is described herein as Teucriogethes huangae Liu & Audisio, sp. nov., and information on its ecology and systematic position is provided. The new species, associated as larvae with a strongly isolated member of the genus Teucrium L. (Lamiaceae), T. ornatum Hemsl., exhibiting a problematic taxonomic position, represents in turn an isolated and morphologically rather aberrant taxon in its lineage, probably the largest in size (2.2-2.8mm), and the first endemic representative of its genus in the whole Eastern Palaearctic. An updating of the taxonomic assessment of members of Teucriogethes and on possible evolutionary relationships with their larval host plants, based on an integrative taxonomy approach, is finally presented. A key to identification of all known species is also introduced. ZooBank: urn:lsid:zoobank.org:pub:E349044B-29A5-416C-85CA-56143C7A29BE.

Review of Asaphes Walker, 1834 (Hymenoptera, Chalcidoidea, Asaphesinae) from Xinjiang, China.

Four species of the cosmopolitan genus Asaphes Walker, 1834 (Hymenoptera: Chalcidoidea: Asaphesinae, family incerta sedis) are recorded from Xinjiang Uyghur Autonomous Region, China, bringing the number of known species in China to eight. In addition to Asaphessuspensus (Nees ab Esenbeck), 1834 and A.vulgaris Walker, 1834, A.fuyunis Li & Zhang, sp. nov. is newly described based on females and A.californicus Girault, 1917, previously known only from North and South America, is newly recorded from China. These four species are differentiated using an integrative taxonomic approach that includes COI barcode data and morphometrics, and are illustrated using macrophotography. Additionally, the 13 described world species of Asaphes are tabulated and females of the eight recognized Chinese species are keyed.

Population genetic structure and ecological differentiation in the bryozoan genus Reteporella across the Azores Archipelago (central North Atlantic)

The processes shaping population dynamics of benthic marine invertebrates with non-planktotrophic larvae are still poorly understood but have seen a renewed interest in applying integrative taxonomic approaches. We used mitochondrial and microsatellite (SSR-GBAS) data to estimate connectivity across islands and seamounts in the central North Atlantic Azores Archipelago in five species of the bryozoan genus Reteporella Busk, 1884. Discordant patterns were inferred between datasets, which might be due to methodological constraints related to the application of multilocus approaches based on amplification to multiple species or due to interspecific introgression in deep waters. A divergent cryptic ecotype of Reteporella atlantica (Busk, 1884) was found in shallow waters, likely resulting from ecologically-driven incipient speciation, posing new questions regarding the role of bathymetrical zonation as a promoter of differentiation. The occurrence of ecologically-driven differentiation and potential interspecific introgression in other bryozoans should be considered, both with potentially important evolutionary and biogeographical consequences. The discovery of incipient species, prompted by ecological factors, calls for the need to consider marine invertebrates when developing conservation strategies in oceanic insular ecosystems.

Lost but not forgotten: Rediscovery of the Ukrainian Lepidurus middendorffii (Braem, 1893) (Branchiopoda: Notostraca) through integrative taxonomy

Abstract The taxonomy of the notostracan LepidurusLeach, 1819 is complicated by a large number of synonymised species and extensive intraspecific variability in many relevant characters. We demonstrate, based on an integrative taxonomic approach, that the Ukrainian populations of Lepidurus are not conspecific with any currently accepted Lepidurus species and assign them to the previously synonymised species Lepidurus middendorffiicomp. nov. (Braem, 1893). This species exemplarily highlights the problems in the taxonomy of Lepidurus. The species was originally described as Apus extensus var. middendorffii (Braem, 1893), but L. extensus is a junior synonym of Lepidurus lubbocki (Brauer, 1873), which is currently treated as a subspecies of Lepidurus apus (Linnaeus, 1758). Our molecular genetic analyses based on mitochondrial COI, 12S, 16S, and nuclear 28S, which included published data, suggest the presence of further, possibly cryptic species that await formal recognition and stress the importance for a more extensive revision of Lepidurus. The original type specimens of L. middendorffii, previously stored at the Museum of Natural History (Wrocław University, Wrocław, Poland), are lost and a neotype is designated. Lepidurus middendorffii is characterised by the dorsal organ position between the ocular tubercle margins, the sharp carapace sulcus spines, the long supra-anal plate with many median spines, a telson length to carapace length ratio 0.18–0.35, and differs by > 9% uncorrected COI p-distances from all other Lepidurus species.

Morphological and Molecular Analyses of Aponurus laguncula Looss, 1907 (Digenea: Lecithasteridae) Parasitic in Atlantic Spadefish Chaetodipterus faber (Broussonet, 1782) (Acanthuriformes: Ephippidae) from Brazilian Coastal Zone.

An integrative taxonomic description of Aponurus laguncula (Lecithasteridae), a digenean parasitic species of Chaetodipterus faber (Acanthuriformes) from Brazilian Southeast, is provided. Morphological techniques, as whole mounted slides, histology and scanning electron microscopy, and molecular analyses supported that integrative description. Fifteen digenean specimens were stained in hydrochloric carmine and mounted on permanent slides. Two specimens were stained in hematoxylin and eosin following histological routine processing. Four parasites were dehydrated through a graded ethanol series, critical point dried with carbon dioxide and coated with gold to scanning electron microscopy analysis. Sequence of the large ribosomal subunit (28S rDNA) gene was generated and used to construct a phylogeny based on maximum likelihood and Bayesian inference analyses. Morphological description and morphometric data obtained in present study were in accordance with previous studies of the species. Use of another morphological techniques, as scanning electron microscopy and histology, corroborated the observed features of whole mounted slides. Also, they provided a better observation of previous reported characteristics and new features reporting, such as an elongated hermaphroditic duct, a smooth tegument and cells that compose the prostatic gland. The molecular sequence obtained in the present study formed a robust clade with available sequences of species of Aponurus. The integrative taxonomic approach successfully combined morphological observations, including both previously reported features and new descriptions from histological and electron microscopy analyses, with molecular data to identify these specimens as A. laguncula. Moreover, the detailed characterization of structures, such as the gonads in A. laguncula, that would be challenging to analyze using a single technique, was possible. Further molecular studies with less conserved genetic markers should be conducted to understand phylogenetic relationships between Aponurus species.

Paronatrema davidbowiei n. sp. (Trematoda: Syncoeliidae), a new parasite of the pelagic thresher (Alopias pelagicus) and its phylogenetic relationships within the suborder Hemiurata Skrjabin & Guschanskaja, 1954

A new species of hemiurid trematode found on the gills and in the aorta of the pelagic thresher Alopias pelagicus from the eastern Pacific, off Costa Rica, is described based on an integrative taxonomic approach that includes the use of light and scanning electron microscopy, and 28S rDNA sequencing. Phylogenetic analysis was also performed to explore, for the first time, the relationships of a member of the subfamily Otiotrematinae within the suborder Hemiurata. Paronatrema davidbowiei n. sp. can be distinguished from the congeners by having tegumental spines on the dorsal surface of the forebody, papillae on the oral sucker, and different morphology or number of testicular follicles. BLAST analysis revealed that sequences of Paronatrema davidbowiei n. sp. had the highest degree of similarity with Hirudinella spp. (Hirudinellidae). Results from Maximum Likelihood and Bayesian phylogenetic analyses, returning trees with the exact same topology and strong branch support, distinguished between the two superfamilies included in the suborder Hemiurata: Azygioidea and Hemiuroidea. Our analysis placed the new species in a clade with Copiatestes filiferus, the only existing sequence of the family Syncoeliidae.

Recent fieldwork and fungarium studies double known diversity of Chlorosplenium and improve understanding of species distributions

ABSTRACT Chlorosplenium is a small genus comprising five species of inoperculate discomycetes in the order Helotiales (Leotiomycetes) often recognizable by their bright yellowish-green colors and gregarious growth on wood. In this study, we describe five new species—C. aotearoa, C. australiense, C. cusucoense, C. epimorsicum, and C. hawaiiense—based on a combination of recent fieldwork and examination of previously collected fungarium specimens. We use an integrative taxonomic approach to support the distinction of new species, incorporating morphology and DNA sequence data with biogeography. Macro- and micromorphological features of apothecia for all species and culture characteristics for four of the five new species are documented. A multilocus phylogeny based on nuc rDNA internal transcribed spacer region ITS1-5.8S-ITS2, partial large subunit nuc ribosomal DNA (28S nuc rDNA), and A–B regions of the largest subunit of RNA polymerase II (RPB1) gene is presented. Additionally, we report Chlorosplenium chlora from Europe for the first time and expand our knowledge of the diversity and distributions of species in this genus in America, Australia, and New Zealand.

Delimitation of Ophioderma teres (Lyman, 1860) and Ophioderma unicolor H.L. Clark, 1940 stat. nov. (Echinodermata: Ophiuroidea), including the description of two new species

Ophioderma teres (Lyman, 1860), an ophiuroid previously believed to have a wide distribution in the eastern Pacific, has been found to have an unclear taxonomic identity. While considered a well-known species, recent studies have revealed that O. teres lacks a holotype and has vague boundaries with its congeners Ophioderma teres unicolor H.L. Clark, 1940 and Ophioderma sodipallaresi Caso, 1986, as well as with two additional new morphotypes detected in Mexico and Nicaragua, causing continuous misidentifications. This study utilized an integrative taxonomy approach based on morphologic, morphometric, and molecular evidence to clarify the taxonomic status of O. teres, O. sodipallaresi, O. teres unicolor, and the two new morphotypes. Data integration led to the following results: 1) the neotype designation and redescription of O. teres; 2) the proposal of O. sodipallaresi as a junior synonym of O. teres; 3) the status change of O. unicolor stat. nov. from subspecies to species, and 4) the description of the morphotypes as the new species Ophioderma aija sp. nov. and Ophioderma bichi sp. nov. An identification key to the eastern Pacific species of Ophioderma was also developed. This work contributes to the knowledge of Ophioderma in the region, increasing the number of described species and providing resources for their accurate identification.

Biogeography and phylogeny of the scavenging amphipod genus Valettietta (Amphipoda: Alicelloidea), with descriptions of two new species from the abyssal Pacific Ocean

Abstract Valettietta Lincoln & Thurston, 1983 (Amphipoda: Alicelloidea) is an infrequently sampled genus of scavenging amphipod, with a known bathymetric range from 17–5467 m encompassing a variety of habitats from anchialine caves to abyssal plains. Molecular systematics studies have uncovered cryptic speciation in specimens collected from the abyssal Pacific, highlighting uncertainty in the description of Valettietta anacantha (Birstein & Vinogradov, 1963). Here, we apply an integrative taxonomic approach and describe two new species, Valettietta trottarum sp. nov. and Valettietta synchlys sp. nov., collected at abyssal depths in the Clarion-Clipperton Zone, Pacific Ocean. Both species can be distinguished by characters of the gnathopods, uropod 3, and the inner plate of the maxilliped. Further, molecular phylogenetic analyses of two mitochondrial (16S rDNA and COI) and two nuclear (Histone 3 and 28S rRNA) regions found both new species to form well-supported clades and allowed us to re-identify previously published records based on genetic species delimitation. The biogeography of Valettietta is discussed in light of these re-evaluated records, and a new taxonomic key to the genus is provided. These new taxa highlight the strength of applying an integrated taxonomic approach to uncover biodiversity, which is critical in regions being explored for potential industrial purposes.

A treasure trove of endemics: two new species of snake-eyed skinks of the genus Panaspis Cope, 1868 (Squamata, Scincidae) from the Serra da Neve Inselberg, southwestern Angola

Four species of the genus Panaspis – P. cabindae, P. wahlbergi, P. maculicollis and P. mocamedensis – are currently known from Angola. The analysis of recently collected specimens from Serra da Neve Inselberg, an isolated mountain located in northern Namibe Province, revealed unexpected taxonomic diversity in the group. Using an integrative taxonomy approach based on morphological and DNA sequence data, with both mitochondrial (16S) and nuclear (RAG-1) genes, we were able to distinguish two distinct populations, described here as two new species, Panaspis ericaesp. nov. and P. mundavambosp. nov. Both species are assumed to be endemic to the inselberg. This reinforces our notion of southwestern Angola as a hotspot of skink diversity, and highlights the urgent need for the conservation of Serra da Neve.

Alike but genetically divergent: The resurrection of Urotrygon asterias (Jordan & Gilbert, 1883) from its closest relatives, the Munda and the Blotched stingray.

The genus Urotrygon comprises small- to medium-sized endemic round rays on the American continent and has undergone several synonymization processes. Here, we used an integrative taxonomic approach, including meristic, morphometric, and mtDNA analyses, to resolve the particularly intricate relationship among Urotrygon munda Gill, 1863, Urotrygon chilensis (Günther, 1872), and Urotrygon asterias (Jordan & Gilbert, 1883). The latter species is currently a synonym of U. munda but is also considered the U. chilensis "northern morphotype." These taxonomic entities have historically been confounded, mainly due to their phenotypical resemblance along their geographic distribution in the eastern Pacific. We assessed 78 specimens (43 "northern" and 30 "southern morphotypes" of U. chilensis, as well as 5 U. munda) using 19 external variables for taxonomic and morphometric analysis. Distinct meristic patterns, including pectoral and pelvic ceratotrichia, vertebrae number, and thorn distribution along the dorsal midline, were observed in the series-type specimens of the three taxonomic entities. Our multivariate morphometric analyses consistently differentiated the three groups as distinct taxonomic entities, with an overall classification accuracy of 66.7%. The meristic results also provided reliable information distinguishing the three entities. Based on the nicotinamide adenine dinucleotide (NADH2) and cytochrome oxidase subunit I (COI) genes, our phylogenetic analysis were consistent with the morphometric and meristic data, supporting these three entities as distinct species having their own evolutionary lineages. Our comprehensive approach confidently demonstrated that the northern U. chilensis morphotype matched and corresponded to the description of the Starry round ray, U. asterias, confirming its taxonomic resurrection as a valid species distinct from U. chilensis and U. munda. The geographic distribution of U. asterias spans from the tropical west coast of Mexico (including the Gulf of California) to Costa Rica, revealing that microevolutionary processes have well-defined population clades within this range. Furthermore, U. chilensis is unequivocally established as the sole Urotrygon species occurring south of the Guayaquil marine ecoregion. In addition, the public COI and NADH2 sequences available for Urotrygon hosted in the ad hoc online databases were found to be misidentified, emphasizing the need for rigorous taxonomic scrutiny in this group. Finally, our research underscores the significance of an integrative approach that combines morphometric, meristic, and molecular techniques with historical data to disentangle the complexities of closely related taxa.

Phylogenetics, Molecular Species Delimitation and Geometric Morphometrics of All Reddish-Brown Species in the Genus Neotriplax Lewis, 1887 (Coleoptera: Erotylidae: Tritomini).

To date, five species of reddish-brown Neotriplax have been described, but their highly similar body color and other phenotypic traits make accurate taxonomy challenging. To clarify species-level taxonomy and validate potential new species, the cytochrome oxidase subunit I (COI) was used for phylogenetic analysis and the geometric morphometrics of elytron, pronotum, and hind wing were employed to distinguish all reddish-brown Neotriplax species. Phylogenetic results using maximum likelihood and Bayesian analyses of COI sequences aligned well with the current taxonomy of the Neotriplax species group. Significant K2P divergences, with no overlap between intra- and interspecific genetic distances, were obtained in Neotriplax species. The automatic barcode gap discovery (ABGD), assemble species by automatic partitioning (ASAP), and generalized mixed Yule coalescent (GMYC) approaches concurred, dividing the similar species into eight molecular operational taxonomic units (MOTUs). Geometric morphometric analysis using pronotum, elytron, hind wing shape and wing vein patterns also validated the classification of all eight species. By integrating these analytical approaches with morphological evidence, we successfully delineated the reddish-brown species of Neotriplax into eight species with three new species: N. qinghaiensis sp. nov., N. maoershanensis sp. nov., and N. guangxiensis sp. nov. Furthermore, we documented the first record of N. lewisii in China. This study underscores the utility of an integrative taxonomy approach in species delimitation within Neotriplax and serves as a reference for the taxonomic revision of other morphologically challenging beetles through integrative taxonomy.

Lebertia litoralis sp. nov. a new water mite described on morphological and molecular characters (Acariformes, Hydrachnidia, Lebertiidae)

An integrative taxonomic approach, combining new morphological data with the analysis of partial COI sequences (DNA-barcodes) is used to describe Lebertia litoralis Zawal & Szenejko sp. nov. from lake habitats in Poland and Norway. The obtained DNA-barcodes of Polish and Norwegian specimens differ only slightly (k = 4.142, Π = 0.006). Morphologically, the new species is most similar to Lebertia porosa Thor, 1900 and L. obscura Thor, 1900, from which it differs by a slenderer shape of the first leg and the position of the distoventral setae of p-4, inserted rather far away from the distal segment edge. http://zoobank.org/urn:lsid:zoobank.org:pub:27F6FFD0-CA98-4FAD-BC16-58FA654E36ED

Delimiting species, revealing cryptic diversity, and population divergence in Qinghai-Tibet Plateau weevils through DNA barcoding.

The Leptomias group represents one of the most diverse taxonomic group of weevils in the Qinghai-Tibet Plateau and its adjacent areas. Despite the potential of hidden diversity, relatively few comprehensive studies have been conducted on species diversity in this taxonomic group. In this study, we performed DNA barcoding analysis for species of the Leptomias group using a comprehensive DNA barcode dataset that included 476 sequences representing 54 morphospecies. Within the dataset, our laboratory contributed 474 sequences, and 390 sequences were newly generated for this study. The average Kimura 2-parameter distances among morphospecies and genera were 0.76% and 19.15%, respectively. In 94.4% of the species, the minimum interspecific distances exceeded the maximum intraspecific distances, indicating the presence of barcode gaps in most species of Leptomias group. The application of Automatic Barcode Gap Discovery, Assemble Species by Automatic Partitioning, Barcode Index Number, Bayesian Poisson tree processes, jMOTU, and Neighbor-joining tree methods revealed 45, 45, 63, 54, and 55 distinct clusters representing single species, respectively. Additionally, a total of four morphospecies, Leptomias kangmarensis, L. midlineatus, L. siahus, and L. sp.9RL, were found to be assigned to multiple subclade each, indicating the geographical divergences and the presence of cryptic diversity. Our findings of this study demonstrate that Qinghai-Tibet Plateau exhibits a higher species diversity of the Leptomias group, and it is imperative to investigate cryptic species within certain morphospecies using integrative taxonomic approaches in future studies. Moreover, the construction of a DNA barcode reference library presented herein establishes a robust foundational dataset to support forthcoming research on weevil taxonomy, phylogenetics, ecology, and evolution.

Endless forms most frustrating: disentangling species boundaries in the Ramalina decipiens group (Lecanoromycetes, Ascomycota), with the description of six new species and a key to the group.

Oceanic islands have been recognized as natural laboratories in which to study a great variety of evolutionary processes. One such process is evolutionary radiations, the diversification of a single ancestor into a number of species that inhabit different environments and differ in the traits that allow them to exploit those environments. The factors that drive evolutionary radiations have been studied for decades in charismatic organisms such as birds or lizards, but are lacking in lichen-forming fungi, despite recent reports of some lineages showing diversification patterns congruent with radiation. Here we propose the Ramalina decipiens group as a model system in which to carry out such studies. This group is currently thought to be comprised of five saxicolous species, all of them endemic to the Macaronesian region (the Azores, Madeira, Selvagens, Canary and Cape Verde islands). Three species are single-island endemics (a rare geographic distribution pattern in lichens), whereas two are widespread and show extreme morphological variation. The latter are suspected to harbor unrecognized species-level lineages. In order to use the Ramalina decipiens group as a model system it is necessary to resolve the group's phylogeny and to clarify its species boundaries. In this study we attempt to do so following an integrative taxonomy approach. We constructed a phylogenetic tree based on six molecular markers, four of which are newly developed and generated competing species hypotheses based on molecular (species discovery strategies based on both single locus and multilocus datasets) and phenotypic data (unsupervised clustering algorithms based on morphology, secondary chemistry and geographic origin). We found that taxonomic diversity in the Ramalina decipiens group has been highly underestimated in previous studies. In consequence, we describe six new species, most of them single-island endemics and provide a key to the group. Phylogenetic relationships among species have been reconstructed with almost full support which, coupled with the endemic character of the group, makes it an excellent system for the study of island radiations in lichen-forming fungi. Citation: Blázquez M, Pérez-Vargas I, Garrido-Benavent I, et al. 2024. Endless forms most frustrating: disentangling species boundaries in the Ramalina decipiens group (Lecanoromycetes, Ascomycota), with the description of six new species and a key to the group. Persoonia 52: 44-93. https://doi.org/10.3767/persoonia.2024.52.03 .