Single Taxonomic Unit Research Articles

Morphological relationships among populations support a single taxonomic unit for the North American Gray Wolf

Abstract The Gray Wolf (Canis lupus) is viewed as one of the most diverse mammal species. In North America, the diversity of its forms is debated, with views conflicting on subspecies designation. The present study aimed to reinvestigate the skull morphometric variation among North American populations while attempting to unveil underlying causal factors. A large sample of vouchered museum skulls, collected from 12 ecogeographical populations spanning the North American range of the species, was examined and 21 craniodental characters were measured. Skull shape showed within-population variations but provided evidence for a high morphological affinity among populations. Allometric analyses also pointed to similar evolutionary paths among populations. However, significant size-related differentiation was revealed within and among populations. Skull size could be related to three insulin-like growth factor-1 gene (IGF-1) alleles. Ecological conditions that should determine prey type and availability accounted for most of the skull size variation. In contrast, no evidence of geographical isolation of populations was detected. The results support the existence of a single morphological pool of North American gray wolf populations that could be equated with one taxonomic unit. This study raises again the question of the diversity of forms in this species in North America and calls into question the validity of previously recognized species and subspecies based on genetics and morphology.

Species identification and genetic relationships in the squid family Gonatidae (Teuthida, Cephalopoda) based on partial sequencing of mitochondrial and nuclear genes

Abstract Squids of the family Gonatidae are key components in oceanic communities. However, issues related to correct species identification, number of species, and their genetic relatedness remain. To address these issues, sequences from three mitochondrial (cytochrome c oxidase subunit I [CO1], 16S rRNA, and 12S rRNA) and two nuclear (18S and 28S) genes were analysed in the Gonatidae. Four of the five sequences (12S rRNA, 16S rRNA, 28S, and CO1) yielded rather similar patterns of genetic relationships among the species. Molecular evidence suggested intra-familial subdivision into two major groups of species having either five or seven longitudinal rows of teeth in the radula. The former group included all species of the genus Gonatus and two sister-species of Gonatopsis s. str. suggesting that all gonatid species with five rows of radular teeth represent a single taxonomic unit of a genus or subfamily level. Species with seven rows of radular teeth formed several ‘species’ clusters. Sequence analysis also addressed species identification issues in the Gonatidae. Two genetically divergent groups were found among squid which conformed to the description of Gonatus berryi. Molecular evidence suggested sister-species relationships between ‘large’ and ‘small’ forms of Boreoteuthis borealis with size-at-maturity as the only reported difference between these two cohorts. Sequence variation was observed within Gonatus pyros. Inclusion of gonatid sequences from the GenBank into the analysis suggested probable species misidentification in several cases. Combined use of several mitochondrial and nuclear sequences served as a valuable tool for species identification and provided a solid background for unravelling molecular genetic and taxonomic relationships in the Gonatidae.

Calanoid Copepods Of China Seas

Calanoid copepods are a well-recognized taxonomic group of Crustacea. They were already placed, with one cyclopoid (Scribella) and five calanoid (Acartia, Calanus, Candacia, Euchirus (= Euchaeta), and Pontella) genera, under a single taxonomic unit, the Calanidae, by Dana [1]. Giesbrecht and Sars are the two early principal contributors to the taxonomy of Copepoda, including the Calanoida. Based on the location of the body articulation, Giesbrecht [2] divided copepods into two groups, the Gymnopleoden and Podopleoden. All copepods, characterized by an articulation between the fifth pedigerous (leg-bearing) somite and genital somite, separating the body into an anterior part (prosome) and a posterior part (urosome), were placed under the suborder Gymnoplea. Podoplea contained all other copepods having this articulation located between the fourth and fifth pedigerous somites. According to the structure of antennules in males, Giesbrecht further divided the Gymnoplea into two tribes, the Amphaskandria (males with both antennules similar) and Heterarthrandria (males with one of the antennules modified). Sars [3-9], on the other hand, suggested seven distinct types of copepods, Calanus, Harpacticus, Cyclops, Notodelphys, Monstrilla, Caligus, and Lernaea, respectively respresenting seven divisions (Suborders) of the Copepoda, i.e., Calanoida, Harpacticoida, Cyclopoida, Notodelphyoida, Monstrilloida, Caligoida, and Lernaeoida. The Calanoida in Sars [3-9], corresponding to the Gymnoplea in Giesbrecht [2], was divided into three sections: Amphascandria (both antennules in males are alike and only transformed slightly without any genicular structure, in the greater number of the genera the adult males are distinguished by a conspicuous transformation and great reduction in oral parts), Isokerandria (both antennules are without any conspicuous difference and oral part of much the same appearance in the two sexes), and Heterarthrandria (one of the antennules in male similar to that in female, the other peculiarly transformed into a powerful grasping organ). Modifications of classification within the Calanoida have then been proposed and were reviewed by Huy & Boxshall [10]. In 1974, Andronov [11] proposed the phylogenetic relationships of the higher taxa within the Order Calanoida, and included nine superfamilies: Augapatiloidea, Bathypontioidea, Centropagoidea, Eucalanoidea, Megacalanoidea, Platycopioidea, Pseudocyclopoidea, Pseudocalanoidea, and Riocalanoidea. As the results of Andronov’s [12] change of names of some superfamilies to conform with the International Code of Zoological Nomenclature and subsequently Boxshall and Halsey’s [13] amendment, the Order Calanoida now consists of ten superfamilies and 43 families (30 families, highlighted in red color, present in the China seas). 1. Superfamily Arietelloidea Sars, 1902 (changed from Augaptiloidea) (24, 134) Family Arietellidae

Genetic and morphological polymorphisms of Aedes scapularis (Diptera: Culicidae), vector of filariae and arboviruses.

Aedes scapularis is a neotropical mosquito that is competent to vector viruses and filariae. It is reputed to be highly morphologically and genetically polymorphic, facts that have raised questions about whether it is a single taxonomic entity. In the last five decades, authors have posed the hypothesis that it could actually be a species complex under incipient speciation. Due to its epidemiological importance, its taxonomic status should be determined with confidence. Our objective was to investigate more deeply the polymorphism of Ae. scapularis to detect any evidence of incipient speciation of cryptic species. We then compared populational samples from the Southeastern, Northern and Northeastern regions of Brazil. The biological markers used in the comparison were: the complete mitochondrial DNA, the isolated mitochondrial gene cytochrome oxidase subunit I (COI) and wing geometry. As expected, high morphological/genetic polymorphism was observed in all Ae. scapularis populations, however it was not indicative of segregation or incipient speciation. There was no correlation between wing shape and the geographical origin of the populations analysed. A congruent observation resulted from the analysis of the COI gene, which revealed a high number of haplotypes (51) and no clusterization of populational samples according to the original biomes. In the phylogenetic analysis of the 13 mitochondrial protein-coding genes, the Ae. scapularis clade clustered with maximum support (100% bootstrap support and posterior probability of 1). No significant internal structure was observed in the Ae. scapularis clade, which was nearly a polytomy. Taken together, our results indicate that this species is not a species complex. We conclude that there was no indication, in the analysed regions, of the occurrence of more than one taxon in the species Ae. scapularis, despite it being highly polymorphic. By ruling out the former species complex hypothesis, our phylogenetic results reinforce that Ae. scapularis is a single taxonomic unit and should be monitored with standardized surveillance and control methods.

Cytogenetic and genetic data support Crossodactylus aeneus Müller, 1924 as a new junior synonym of C. gaudichaudii Duméril and Bibron, 1841 (Amphibia, Anura).

The nominal anuran species Crossodactylus gaudichaudii Duméril and Bibron, 1841 and Crossodactylus aeneus Müller, 1924 are indistinguishable based on adult and larval morphology, being subject of taxonomic doubts. Here, we describe the karyotypes of C. gaudichaudii and C. aeneus, using classical and molecular cytogenetic markers. In addition, we used sequences of the H1 mitochondrial DNA to infer their phylogenetic relationships by Maximum Likelihood (ML) and Maximum Parsimony (MP) approaches and species delimitation test (by bPTP approach). The karyotypic data do not differentiate C. gaudichaudii and C. aeneus in any of the chromosome markers assessed. In both phylogenetic analyses, C. gaudichaudii and C. aeneus were recovered into a strongly supported clade. The species delimitation analysis recovered the specimens assigned to C. gaudichaudii and C. aeneus as a single taxonomic unit. Taken the cytogenetic and genetic results together with previous studies of internal and external morphology of tadpoles and biacoustic pattern, C. gaudichaudii and C. aeneus could not be differentiated, which supports the hypothesis that they correspond to the same taxonomic unit, with C. aeneus being a junior synonym of C. gaudichaudii.

Revision of taxonomic status of Anthrenus pimpinellae isabellinus (Coleoptera: Dermestidae)

For 160 years, Anthrenus pimpinellae isabellinus Kuster, 1848 has been considered a subspecies of A. pimpinellae Fabricius, 1775. However, habitus shape differs between the subspecies with A. p. isabellinus being broader than A. p. pimpinellae and resembling more closely A. dorsatus Mulsant & Rey, 1868. Here A. p. pimpinellae and A. p. isabellinus, are examined to look for evidence that they comprise a single taxonomic unit. Habitus and genital structures are considered, and the universal animal barcode region of the mitochondrial cytochrome oxidase I gene is sequenced. The results of the morphological, morphometric, and genetic analyses mirror each other perfectly and suggest that A. p. isabellinus is the same species as A. dorsatus rather than being a subspecies of A. pimpinellae. The very small intraspecific DNA sequence variation supports the view that A. dorsatus and A. p. isabellinus belong to a single species that diverges considerably from A. p. pimpinellae. Morphology, including genital structure, is congruent with the genetic data and provides a powerful way of resolving species organisation in these widespread beetles. In view of these findings, Anthrenus isabellinus Kuster, 1848 is restored to full species status and Anthrenus dorsatus Mulsant & Rey, 1868 becomes its new junior subjective synonym.

Genetic insights into the globally invasive and taxonomically problematic tree genus Prosopis.

Accurate taxonomic identification of alien species is crucial to detect new incursions, prevent or reduce the arrival of new invaders and implement management options such as biological control. Globally, the taxonomy of non-native Prosopis species is problematic due to misidentification and extensive hybridization. We performed a genetic analysis on several Prosopis species, and their putative hybrids, including both native and non-native populations, with a special focus on Prosopis invasions in Eastern Africa (Ethiopia, Kenya and Tanzania). We aimed to clarify the taxonomic placement of non-native populations and to infer the introduction histories of Prosopis in Eastern Africa. DNA sequencing data from nuclear and chloroplast markers showed high homology (almost 100 %) between most species analysed. Analyses based on seven nuclear microsatellites confirmed weak population genetic structure among Prosopis species. Hybrids and polyploid individuals were recorded in both native and non-native populations. Invasive genotypes of Prosopis juliflora in Kenya and Ethiopia could have a similar native Mexican origin, while Tanzanian genotypes likely are from a different source. Native Peruvian Prosopis pallida genotypes showed high similarity with non-invasive genotypes from Kenya. Levels of introduced genetic diversity, relative to native populations, suggest that multiple introductions of P. juliflora and P. pallida occurred in Eastern Africa. Polyploidy may explain the successful invasion of P. juliflora in Eastern Africa. The polyploid P. juliflora was highly differentiated from the rest of the (diploid) species within the genus. The lack of genetic differentiation between most diploid species in their native ranges supports the notion that hybridization between allopatric species may occur frequently when they are co-introduced into non-native areas. For regulatory purposes, we propose to treat diploid Prosopis taxa from the Americas as a single taxonomic unit in non-native ranges.

A revision of the diagnosis and affinities of the metriorhynchoids (Crocodylomorpha, Thalattosuchia) from the Rosso Ammonitico Veronese Formation (Jurassic of Italy) using specimen-level analyses.

Neptunidraco ammoniticus is a thalattosuchian crocodylomorph from the Rosso Ammonitico Veronese Formation (RAVF, Middle Jurassic) of northern Italy. Erected from one partial specimen, Neptunidraco is pivotal in reconstructing thalattosuchian evolution, being it the oldest known member of Metriorhynchidae. Two additional RAVF thalattosuchians have been referred to Neptunidraco. A revised diagnosis of N. ammoniticus is provided here. Using a well-sampled phylogenetic data set of Crocodylomorpha, the affinities of all three RAVF thalattosuchian specimens are investigated simultaneously for the first time using parsimony tree-search strategies and Bayesian inference using the Fossilized Birth-Death with Sampled Ancestor (FBDSA) model. The results of the alternative analyses are not consistent in the placement of the RAVF specimens. The holotype of N. ammoniticus is consequently referred to Metriorhynchidae incertae sedis. The first referred specimen is recovered in various alternative placements among Metriorhynchoidea. The third and most fragmentary specimen is recovered as a crocodylomorph of uncertain affinities in the parsimony analysis and in the undated Bayesian analysis, and a metriorhynchoid sister taxon of the second RAVF specimen in the tip-dated Bayesian analysis. Only a subset of the results in the parsimony-based analyses supports the referral of the latter two specimens to Neptunidraco. The unusually high rate of morphological divergence for the Neptunidraco branch, inferred in previous iterations of the Bayesian inference analyses but not recovered in the novel analysis, was likely an artifact of the a priori constraint of all RAVF thalattosuchians into a single taxonomic unit, and of the arbitrarily fixed tip-age priors for the terminal taxa. These results confirm the utility of specimen-level morphological analysis and of combined tree-search strategies for inferring the affinities and the inclusiveness of fragmentary but significant fossil taxa, and reinforce the importance of incorporating stratigraphic uncertainty as prior in tip-dated Bayesian inference analyses.

Phylogeography of the reticulated python (Malayopython reticulatus ssp.): Conservation implications for the worlds' most traded snake species.

As an important economic natural resource in Southeast Asia, reticulated pythons (Malayopython reticulatus ssp.) are primarily harvested from the wild for their skins—which are prized in the luxury leather goods industry. Trade dynamics of this CITES Appendix II listed species are complex and management approaches on the country or regional level appear obscure. Little is known about the actual geographic point-of-harvest of snakes, how genetic diversity is partitioned across the species range, how current harvest levels may affect the genetic viability of populations, and whether genetic structure could (or should) be accounted for when managing harvest quotas. As an initial survey, we use mitochondrial sequence data to define the broad-scale geographic structure of genetic diversity across a significant portion of the reticulated python’s native range. Preliminary results reveal: (1) prominent phylogenetic structure across populations east and west of Huxley’s modification of Wallace’s line. Thirty-four haplotypes were apportioned across two geographically distinct groups, estimated to be moderately (5.2%); (2) Philippine, Bornean and Sulawesian populations appear to cluster distinctly; (3) individuals from Ambon Island suggest recent human introduction. Malayopython reticulatus is currently managed as a single taxonomic unit across Southeast Asia yet these initial results may justify special management considerations of the Philippine populations as a phylogenetically distinct unit, that warrants further examination. In Indonesia, genetic structure does not conform tightly to political boundaries and therefore we advocate the precautionary designation and use of Evolutionary Significant Units within Malayopython reticulatus, to inform and guide regional adaptive management plans.

Assembling the challenging puzzle of algal biodiversity: species delimitation within the genus Asterochloris (Trebouxiophyceae, Chlorophyta).

The genus Asterochloris represents one of the most common, widespread, and diverse taxa of lichen photobionts. In this report, we describe and characterize six new species (A.echinata, A.friedlii, A.gaertneri, A.leprarii, A.lobophora, and A.woessiae) that were identified during our recent investigation of photobiont diversity. We found that the species differed genetically, morphologically, ecologically, and with respect to their mycobiont partners. Statistical analyses revealed significant morphological differentiation of all six newly described species, as well as their separation from previously described Asterochloris species. Chloroplast morphology represented the best morphological marker for species delineation. In fact, each species can be recognized by the dominance and unique assemblage of particular chloroplast types. Although genetically well recognized by rapidly evolving internal transcribed spacer rDNA and actin intron markers, all 13 investigated Asterochloris species shared identical small subunit rDNA sequences. We therefore demonstrated that morphologically and ecologically diverse species can frequently be grouped into a single taxonomic unit in whole-transcriptome sequencing studies, considerably affecting the resulting estimates of species diversity. Finally, we demonstrated the presence of isogamous sexual reproduction in Asterochloris, disputing the current symbiotic dogma of the loss of sexual reproduction in algal symbionts.

Thesis Abstract Morphological and phylogeographic analysis of Brazilian tortoises (Testudinidae).

Thesis Abstract Morphological and phylogeographic analysis of Brazilian tortoises (Testudinidae).

Emendation and taxonomic revision of Miscellanea juliettae pfenderae and M. juliettae villattea with designation of the respective holotype

The description of two subspecies, Miscellanea juliettae pfenderae Leppig and M. juliettae villattea Leppig, is emended and a new holotype is designated. Both subspecies were previously described as subordinate units of Miscellanea juliettae, a species that has never been formally described. Here we provide the formal description of the species Miscellanea juliettae n. sp., and show that both subspecies are intergrading units of the same species. This results in retaining a single taxonomic unit, Miscellanea juliettae n. sp., leading us to abandon previous designations of subspecies rank.

Legume (Mimosoideae) fossil woods from the Late Miocene (Salicas Formation) of northwestern Argentina

Six pieces of fossil wood from the late Miocene of Northwestern Argentina (Salicas Formation) are described. They are all assigned to Prosopisinoxylon anciborae Martinez based on the presence of the following diagnostic characters: vessels of two distinct diameter classes, simple perforation plates, vestured pits, abundant axial parenchyma and wide rays. Signifi cant anatomical variation exists among specimens but they are regarded as a single taxonomic unit because usually a gradual transition is observed among most variable characters. A principal component analysis (PCA) was performed and results agree with the taxonomic placement. The analysis also shows discrete clusters of other related Leguminosae fossil- genera. Wood anatomy suggests a warm and dry climate for the zone supporting previous studies.

From Asia to Europe across Siberia: phylogeography of the Siberian spined loach (Teleostei, Cobitidae)

We assessed the genetic variability of the Siberian spined loach Cobitis melanoleuca across its unusually broad distribution that encompasses areas greatly affected by Pleistocene glaciations. Due to extensive morphological variation among their populations, the taxonomic status of C. melanoleuca is complicated. It is unclear whether C. melanoleuca represents a single taxonomic unit or contains several species or subspecies. Our analyses showed low genetic variability in all populations without any phylogenetic structure. The absence of molecular distinctiveness indicates the conspecificity of all C. melanoleuca populations. Only a few common haplotypes shared by East Asian, Siberian and European populations were found at high frequency in the nuclear genes analysed. At the mitochondrial level, Siberian populations shared haplotypes with populations located at both extremes of the species’ range suggesting central populations as a source of current mitochondrial variability. Unimodal mismatch distributions and significant values from neutrality tests support a recent expansion of C. melanoleuca. Our time estimates suggest a postglacial colonisation of European waters around 1.0 MYA, indicating that C. melanoleuca may represent the last cobitid immigrant in Europe that used the northern route across Siberia to expand its range.

Genetic structure of the western pygmy possum, Cercartetus concinnus Gould (Marsupialia: Burramyidae) based on mitochondrial DNA

Cercartetus concinnus Gould (Marsupialia: Burramyidae) has a spatially disjunct distribution, with a broad stretch of saltbush on the Nullarbor Plain forming an apparent barrier between the population: one in southern Western Australia, and another in south-eastern Australia, encompassing South Australia, Victoria, and New South Wales. This disjunct distribution and slight differences in morphology between western and eastern populations have led to conjecture about the taxonomy of this species. This study assessed the taxonomic status of C. concinnus across southern Australia. Analyses using the mitochondrial (mtDNA) ND4 gene showed little phylogeographic structure throughout the wide range of C. concinnus in southern Australia; closely related haplotypes (~0.1% sequence divergence) had a wide distribution from Western Australia to South Australia, suggesting recent genetic connectivity. These data indicate that C. concinnus populations represent a single taxonomic unit (Evolutionarily Significant Unit) throughout the geographic range. Further research is required to assess the impact of recent population fragmentation and whether an erosion of genetic variation in isolated populations has occurred.

Attempts to molecularly distinguish cryptic taxa in Anopheles gambiae s.s.

Analyses of inversions in polytene chromosomes indicate that, in West Africa, Anopheles gambiae (sensu stricto) may be a complex of more than a single taxonomic unit, and these units have been called chromosomal forms. In order to determine whether this genetic discontinuity extends to the rest of the genome, as would be expected if reproductive isolation exists, we have sequenced several regions of both the nuclear and mitochondrial genomes. With one exception, we were unable to identify any nucleotide sites that differentiate the chromosomal forms. The exception was the internal transcribed spacer (ITS) of the ribosomal DNA (rDNA). Three sites in this region distinguish Mopti chromosomal form from Savanna and Bamako in Mali and Burkina Faso. However, outside these two countries, the association between chromosomal form and rDNA type does not always hold. Together with the variants in the rDNA intergenic spacer (IGS) described in the accompanying papers (della Torre et al., 2001; Favia et al., 2001), we can recognize two major types of rDNA, Type I and Type II (corresponding to molecular forms S and M in della Torre et al., 2001). Type I is widespread in West Africa and is the only type found outside of West Africa (i.e. Tanzania and Madagascar). Type II is confined to West Africa. We were unable to detect any heterozygosity for the ITS types even in five collections containing both types. A sample from the island of São Tomé could not be classified into either Type I or Type II as the rDNA had characteristics of both. In general, our results confirm that An. gambiae is not a single pan-mictic unit, but exactly how to define any new taxa remains problematic. Finally, we have found minor variants of the major rDNA types fixed in local populations; contrary to most previous studies, this suggests restricted gene flow among populations of this species.

The systematic significance of the endothecium in Begoniaceae

The endothecial thickening patterns in 173 species, representing the three genera of Begoniaceae, were investigated using cleared macerated anthers. Begoniaceae contain taxa with U-shaped thickenings, perforate base plates, entire base plates, tympanate base plates, anticlinal bars, and taxa that lack endothecial thickenings. The degree of correlation between these endothecial classes and accepted taxonomic boundaries varies: some classes are confined to a single taxonomic unit (e.g. absence of thickenings, non-perforate tympanate base plates) while others are present in several taxonomic units (e.g. U-shapes, perforate base plates). This study provides an improved understanding of the diversity of endothecial patterns in a large genus and indicates that in the Begoniaceae the endothecium is of moderate systematic value within and between closely related sections inBegonia and in Symbegonia. We conclude that the endothecium exhibits high levels of homoplasy between distantly related sections of Begonia. In addition, we show that in contrast to past observations of the endothecium in dicotyledons, apical anther dehiscence in the Begoniaceae is not correlated with a loss of endothecial thickening.

Information Length: Spatial and Temporal Parameters among Stream Bacterial Assemblages

Bacteria, while known to be an integral part of all ecosystems, are seldom studied except as a single taxonomic unit. Few ecological studies even acknowledge the extraordinary functional and species diversity of bacteria. Recent research has elucidated some important facts about bacteria in stream ecosystems. For instance, the dynamics of bacterial genomes within a stream suggest that populations of these organisms are more stable temporally than spatially. We develop predictive models and testable hypotheses based on the information spiraling concept to describe the ecology of stream bacteria and to define 2 new terms: colonization distance and information length. Colonization distance (D_c) is the maximum distance downstream from original colony establishment at which a new colony of bacteria can be established. Information length (L_I) is defined as the maximum length over which a gene has an effect on an ecosystem process independent of a specific host. These terms are modeled relative to the average temporal energy load (joules/min) in the stream. Energy inputs that exceed biologically defined limits of use result in ecosystem energy leaks regardless of information length. Our models predict that information length should be shorter in montane streams than in Coastal Plain streams of southeastern USA. Furthermore, assuming equal average energy load between streams, the stream with the largest energy load variance will leak more energy downstream. Therefore, temperate streams should be less efficient than tropical streams at utilizing energy within a reach.

The cassava green mite in Africa: One or two species? (Acari: Tetranychidae)

Despite a certain amount of confusion that has prevailed for several years with respect to theMononychellus complex (cassava green mite=CGM; Acari: Tetranychidae) which attacks cassava plantations in Africa, strong arguments indicate that a single taxonomic unit corresponding to the speciesMononychellus progresivus Doreste, 1981, was introduced in 1971 from South America.

On the anatomy of wood showing affinities with the genus vertebraria royle, from the irati formation, state of São Paulo, Brazil

Results of research on permineralized wood samples from the Irati Formation (middle to upper Permian) in the State of São Paulo, Brazil add to our understanding of several questionable problems concerning samples showing affinities with the vertebrarian types of axes. A new xylic structural plan including even roots and stems would have been characterized throughout Gondwanaland from post-glacial time through the Late Permian. Until now a number of samples had been described as a single taxonomic unit under the designation of Vertebraria indica Royle 1939. Presumably this taxon does not include only a single generic group, but rather it represents a complex of forms distributed throughout Gondwanaland that are grouped together on the basis of important and similar features, such as: 1) wedge-shaped stelic configuration resembling that of the vertebrarian stelic plan; 2) wavy grouwth rings and asymmetric growth of the vascular cilynder resulting from the cambial activity of ray cells and parenchyma cells in the rings; 3) a frequent and peculiar pitting arrangement on the radial walls of the tracheids which now appears to be also a common feature among glossopteridean shoots and vertebrarian axes. It was possible to identify some samples as independent and definite genera on the basis of their well-preserved leaf and root traces, their nodal structures and also their very characteristic manner of issuing adventitious branches. Eventhough they are not classified in the genus Vertebraria, they are closely comparable in many aspects to axes of this genus. A discussion is presented here of the genus Vertebraria and it is concluded that the related genus Tordoxylon Krãusel 1956 is a valid taxon that can be distinguished within the vertebrarian complex on the basis of its characteristic xylic plan. Some problems concerning taxonomic names are also discussed. A preliminary account of the paleoecological significance of these anatomical structures is presented in view of their rapid rise and extinction during geologic time.