Wide Range Of Morphological Diversity Research Articles

Agro-morphological characterization of bottle gourd [Lagenaria siceraria (Mol.) Standl.] germplasms in Garo Meghalaya hills,

The field experiment was carried out at Horticulture Farm, Department of Horticulture, North Eastern Hill University to evaluate bottle gourd germplasms for horticultural traits and to identify superior genotypes in 30 local bottle gourd genotypes during 2018 and 2019. The experiment was conducted using a randomized block design with three replications. The germplasm lines have been collected from places of Garo Hills districts of Meghalaya. The collected accessions exhibited a wide range of morphological diversity for qualitative as well as for quantitative traits. The grand mean of yield of marketable fruit (kg/plant) was 32.39 kg with the lowest fruit yield/plant of 14.87 kg recorded in GHA-18 and the highest fruit yield of 63.74 kg, fruit yield/plant recorded in GHGA-8. A wide range of variation was recorded for all the characters which indicated that there was better scope for selection for the improvement of these characters.

Two new freshwater species of Surirella (Bacillariophyta) from the Wuling Mountains, China.

Two sympatric Surirella species found at the same specific locality in the Wuling Mountains of China are documented with light and scanning electron microscope. Both species are new to science and named S.wufluminensis sp. nov. and S.suiningensis sp. nov. Surirellawufluminensis has large frustules that are either clockwise or counterclockwise twisted when viewed with the light microscope, and possesses distinctive fibulae, mound-like outgrowths on the valve surface throughout, raised longitudinal ridges on both sides of the raphe, and two helictoglossa-like processes at one apex internally. Surirellasuiningensis has narrowly ovate valve outline, distinctive fibulae, troughs alternating with crests from pole to pole, and two helictoglossa-like processes at one apex internally. These two species do not produce costae on the valve surface in contrast to many species in Surirella. This study provides a further two examples of the wide range of morphological diversity in the genus Surirella.

Separated from the cradle: A new species of Falcidens (Mollusca, Aplacophora, Caudofoveata) reveals weird patterns of distribution in the deep-sea

The shell-less, worm-like caudofoveate aplacophorans are common inhabitants of the deep-sea. A recent series of studies has demonstrated their phylogenetic, ecological and biogeographical importance for the understanding of marine environments. Falcidens Salvini-Plawen, 1968 is among the most speciose genera of Caudofoveata, including species with a wide range of morphological diversity. Here, F. amiae sp. nov. is described based on its body shape, sclerites, and radula; it is compared with other similar species, and distributions are also modelled to envisage other suitable areas of occurrence. Collected over a large area of the southwestern Atlantic Ocean, along the Brazilian coast, most specimens were found in bottom samples from the upper continental slope. Falcidens amiae sp. nov. has a stoutish body without externally perceptible divisions, a “U”-shaped oral shield, a radula with two pairs of teeth, and sclerites with a wide base and acute blade ornamented with a strong central longitudinal keel and weak grooves. While almost all species of Falcidens have elongated bodies with externally perceptible divisions, only two known species have a more-stoutish and homogeneous body shape, F. limifossorides Salvini-Plawen, 1992 and F. halanychi Schander, Scheltema and Ivanov, 2004, comparable to that of F. amiae sp. nov.; they are also similar in the radula structure and F. amiae sp. nov. has an oral shield and sclerites that are markedly similar to those of F. limifossorides. These taxa appear to form a clade, but if so, they apparently became separated long ago, as they now have very distinct distributions. Maps of potential distributions showed that F. amiae sp. nov. and F. halanychi do not overlap in the Atlantic. This study fills a small gap in knowledge of the morphology of this intriguing molluscan group, revealing part of its puzzling distribution in the deep sea.

Assembly of the non-heading pak choi genome and comparison with the genomes of heading Chinese cabbage and the oilseed yellow sarson.

Summary Brassica rapa displays a wide range of morphological diversity which is exploited for a variety of food crops. Here we present a high‐quality genome assembly for pak choi (Brassica rapa L. subsp. chinensis), an important non‐heading leafy vegetable, and comparison with the genomes of heading type Chinese cabbage and the oilseed form, yellow sarson. Gene presence–absence variation (PAV) and genomic structural variations (SV) were identified, together with single nucleotide polymorphisms (SNPs). The structure and expression of genes for leaf morphology and flowering were compared between the three morphotypes revealing candidate genes for these traits in B. rapa. The pak choi genome assembly and its comparison with other B. rapa genome assemblies provides a valuable resource for the genetic improvement of this important vegetable crop and as a model to understand the diversity of morphological variation across Brassica species.

Skeletal Anatomy of the Bigeye Sand Tiger Shark, Odontaspis noronhai (Lamniformes: Odontaspididae), and Its Implications for Lamniform Phylogeny, Taxonomy, and Conservation Biology

Lamniformes (Chondrichthyes: Elasmobranchii) is a group of sharks that consists of 15 extant species with a wide range of morphological diversity. The most rarely captured lamniform is Odontaspis noronhai, and many aspects of its biology remain unknown to date. In this study, the skeletal anatomy of a previously described specimen of O. noronhai was examined using computed tomography. The new skeletal data were then added to a previously published morphology-based character matrix to conduct a new phylogenetic analysis of the Lamniformes. Our phylogenetic study strongly suggests non-monophyly of Odontaspididae, that traditionally consisted of Carcharias taurus, O. ferox, and O. noronhai. Thus, the family Carchariidae is formally resurrected for the genus Carcharias to separate it from the family Odontaspididae sensu stricto for Odontaspis. The overall topology of our phylogenetic trees is similar to that of previously published morphology-based trees and drastically different from the tree topology generally attained by molecular data that cluster Alopias, Megachasma, Odontaspis, and Pseudocarcharias together as a separate clade. The major topological discrepancy between molecular and morphological trees may be attributed to unconventionally asynchronous rates between morphological and molecular evolution, at least in certain species within the Lamniformes, along with likely manifestation of mosaic evolution. The recognition of the family Carchariidae is important to conservation biology, because the extinction of C. taurus would not only mean the elimination of the genus Carcharias, but also the entire family Carchariidae. Our study demonstrates the importance of the integration of both morphological and molecular information to understand organismal evolution.

Synthesis of Diverse Green Carbon Nanomaterials through Fully Utilizing Biomass Carbon Source Assisted by KOH

With multiple properties, green carbon nanomaterials with high specific surface area have become extensively attractive as energy storage devices with environmental-friendly features. The primary synthesis attempts were based on alkalis activation, which, however, faced the dilemma of low utilization rate of carbon sources. Herein, the green carbon with ultrahigh surface area (up to 3560 m2/g) was prepared by the KOH-assisted biomass carbonization. Moreover, the redundant K2O steam and CxHy flow were further utilized; as a result, the carbon materials with a wide range of morphological diversity were collected on the Cu foam. Accordingly, we carried out density functional theory simulations to reveal the mechanism of O-adatom-promoted CH4 dissociation over the Cu surface for carbon formation. The electrodes of electrochemical capacitor fabricated by carbon synthesis possess a 170% higher specific capacitance compared with commercial carbon electrodes. As such, this strategy might be promising in developing hierarchical carbons along with sufficient carbon sources for broadening their potential applications.

Induction of squamous cell carcinoma after MAP3K8 overexpression in murine salivry gland epithelial cells.

Salivary gland neoplasms are relatively rare and comprise only 1%-4% of all human neoplasms. Salivary gland neoplasms also show an extremely wide range of morphological diversity. Currently, the genetic alterations and corresponding molecular mechanisms underlying salivary gland neoplasms development remain largely unknown. We generated an inducible Tet-MAP3K8::MMTV-rTA mouse model by crossing the MAP3K8 transgenic mice with MMTR-rTA transgenic mice to express MAP3K8 in the salivary gland. MAP3K8 overexpression in the murine salivary glands of Tet-MAP3K8::MMTR-rTA transgenic mice induces tumorigenesis. Pathological investigations reveal partial fibrosis and adenosis of salivary glands, and foci of atypical squamoid cellular proliferation, which represent invasive squamous cell carcinoma (SCC). MAP3K8 overexpression is associated with SCC development in murine salivary glands. It provides an in vivo framework for the understanding of molecular mechanisms underlying SCC development in the salivary glands and also for the development of a future therapeutic strategy targeting this tumor type.

The Stratigraphic, Palaeobiogeographic and Phylogenetic Significance of <i>Aquilapollenites</i>

Angiosperm evolved and diversified during Cretaceous. During this course of evolution and radiation, various pollen of uncertain origin had evolved. Aquilapollenites represents the early stock of angiosperms attaining its acme with respect to diversity and dominance during Campanian and Maastrichtian age. It was globally present (except Antarctica) however more dominant in northern hemisphere (Canada, North America, Sakhlain Oblast and China). In India, the Aquilapollenites sp. is present in Maastrichtian aged deposits. The pollen affinity has been associated with Loranthaceae and Santalaceae plant families. Here, a comparative description of all the Aquilapollenites sp. comprising a wide range of morphological diversity has been discussed. The wider morphological diversity and ecological adaptability of Aquilapollenites sp. infer that it is globally significant and warrants a more detailed study.

Morphological diversity in a barley composite cross-derived population evolved under low-input conditions and its relationship with molecular diversity: indications for breeding

SUMMARYIn order to reduce the environmental impact of agriculture and improve the resilience and sustainability of our food systems, there is an increasing interest in shifting from the present agricultural systems, which are characterized by high external inputs, to low-input productive systems characterized by high resilience and sustainability. Purposely developed varieties are needed for the latter. With the rapid disappearance of landraces, heterogeneous populations such as composite cross populations (CCPs) or line mixtures, developed through evolutionary plant breeding, could be the ideal source of breeding material for the development of new cultivars for low-input productive systems. Parental lines of CCPs should be selected among old breeding lines, varieties or landraces because the specific characteristics required for low-input or organic farming systems might have been lost during selection of modern varieties. In the current scenario of renewed interest in evolutionary plant breeding, the evolution of diversity in heterogeneous populations needs to be better investigated to maximize the advantages that can be obtained by their utilization.The present paper reports on the analysis of 88 barley plants chosen randomly from a CCP, namely AUT DBA (where AUT indicates autumn sowing and DBA is the acronym of the former Department) that was multiplied for 13 years under a low-input management system without any conscious human selection, aiming to investigate the morphological diversity still existing in the population and its potential value as source of breeding material for low-input/organic agriculture and understanding the traits that contributed to the adaptive success of certain groups of individuals.Eighteen plant and spike morphological traits were analysed using bi-dimensional spatial analysis, cluster analysis, non-parametric tests and multivariate approaches. Low lodging and loose smut damage were observed in the CCP where several individuals were superior to the best control for at least one of the four yield-related traits, namely spike weight, number of seeds per spike, weight of seeds in a spike and grain weight. Three morphological clusters were identified using cluster analysis. Clusters 2 and 3 grouped the largest number of CCP individuals which, compared with those in cluster 1, were characterized mainly by heavier spikes with higher seed number, taller culms and early flowering. Interestingly, the plant architecture of all the controls was different from that of the most frequent genotypes in the CCP, showing that low-input systems may require a plant architecture different from the one usually considered as the most suitable for high-input systems. Taking advantage of results from Raggiet al. (2015), phenotypic data were also analysed according to individual genetic group assignment. Results suggest that plant height at the beginning of stem elongation, and days to heading, together with traits related to culm and leaf morphology, could have played a significant role in determining the success of plants from genetic group D, which is the group most represented in the CCP.According to the wide range of morphological diversity existing in the AUT DBA and the high percentage of lines that show favourable combinations of different traits, this population could be a useful gene-pool from which to select lines for breeding activities. Even though further use of the CCP for breeding purposes may be limited by its possible evolution, there are different ways of manipulating the CCP to counteract the undesirable changes without great economic and/or technical efforts. The high number of multi-locus genotypes and the evolutionary responses observed in AUT DBA show that the prediction that phenotypic micro-evolution in natural systems may be limited by low genetic variances in harsh environments and low selection pressure in good environments is not necessarily true for low-input systems.

Morphology and Structure of Ultraluminous Infrared Galaxies at z ∼ 2 in the EGS Field

Using the high-resolution F160W images observed by the HST WFC3 (Hubble Space Telescope Wide Field Camera 3) in the CANDELS-EGS (Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey-Extended Groth Strip) field, we have studied the morphological and structural features of 9 ultraluminous infrared galaxies (ULIRGs) at z ∼ 2. We find a wide range of morphological diversity for these ULIRGs, from ellipsoids to multiple bright nuclei or diffuse structures, e.g., the double nuclei, gaseous bridges, dual asym- metries, irregular or elliptical structures. In order to study the morphology of these ULIRGs quantitatively, their morphological parameters (the Gini coeffcient G and moment index M20) are measured in the rest-frame optical wave- band. Compared with the low-redshift counterparts, the high-redshift ULIRGs show a smaller value of G and a larger value of M20, indicating a less concen- tricity and a larger asymmetry of the stellar population distribution in these ULIRGs. Based on a 2-D fitting of the brightness profiles of these ULIRGs, we have derived their effective radii, which are distributed in a range from 2.4 to kpc, with a mean value of (3.9 ± 1.1) kpc. Moreover, we find that in average the sizes of the high-redshift ULIRGs are one to two times smaller than those of the nearby star-forming galaxies of analogous stellar mass. Our results are consistent with those of other studies under the similar conditions of redshift and infrared luminosity.

Resolving phylogenetic relationships of the recently radiated carnivorous plant genus Sarracenia using target enrichment

The North American carnivorous pitcher plant genus Sarracenia (Sarraceniaceae) is a relatively young clade (<3 million years ago) displaying a wide range of morphological diversity in complex trapping structures. This recently radiated group is a promising system to examine the structural evolution and diversification of carnivorous plants; however, little is known regarding evolutionary relationships within the genus. Previous attempts at resolving the phylogeny have been unsuccessful, most likely due to few parsimony-informative sites compounded by incomplete lineage sorting. Here, we applied a target enrichment approach using multiple accessions to assess the relationships of Sarracenia species. This resulted in 199 nuclear genes from 75 accessions covering the putative 8–11 species and 8 subspecies/varieties. In addition, we recovered 42kb of plastome sequence from each accession to estimate a cpDNA-derived phylogeny. Unsurprisingly, the cpDNA had few parsimony-informative sites (0.5%) and provided little information on species relationships. In contrast, use of the targeted nuclear loci in concatenation and coalescent frameworks elucidated many relationships within Sarracenia even with high heterogeneity among gene trees. Results were largely consistent for both concatenation and coalescent approaches. The only major disagreement was with the placement of the purpurea complex. Moreover, results suggest an Appalachian massif biogeographic origin of the genus. Overall, this study highlights the utility of target enrichment using multiple accessions to resolve relationships in recently radiated taxa.

Seed diversity in the tribe Miconieae (Melastomataceae): taxonomic, systematic, and evolutionary implications.

Miconieae is the largest tribe in the Melastomataceae with over 1,850 species. The members of Miconieae display a wide range of morphological diversity, and seed morphology is no exception. Previous studies have found that seed morphological diversity is not congruent with traditional classifications, and suggest that it may reflect evolutionary relationships within Miconieae. Here we characterize seed morphology of 364 species of Miconieae. The morphological data set and a DNA sequence data matrix were analyzed under a parsimony and Bayesian framework. Seed characters were used to test taxonomic and clade hypotheses, to estimate morphological ancestral character states, and to assess phylogenetic signal. The phylogenetic analyses of morphological data retrieved a poorly-resolved, low-supported phylogeny; in contrast, a relatively strongly supported phylogeny was estimated using the molecular data. Hypothesis testing procedures could only reject the monophyly of Clidemia, Leandra, and Miconia. The results indicated that the seed morphological characters were homoplasious, but contained phylogenetic signal. The morphological seed types that were described in previous studies did not support any of the clades retrieved by the molecular phylogeny. In contrast with previous investigations, our study shows that although seed morphology is very variable, it does not provide information for supporting some genera or clades within Miconieae. However, it is suggested that seed characters in combination with other vegetative and reproductive traits may aid in the characterization of smaller clades. The presence of phylogenetic signal retrieved by homoplasious characters may indicate that diversification of seed characters could have an adaptive component. Further studies that increase taxon sampling, refine seed trait characterization, and evaluate the alleged relationships between environmental variables and seed diversification will contribute to a better understanding of seed morphology and evolution in this species-rich tribe.

Larachelus morla, gen. et sp. nov., a new member of the little-known European Early Cretaceous record of stem cryptodiran turtles

ABSTRACT A relatively diverse record of European Early Cretaceous pan-cryptodiran turtles has been revealed from the analysis of new specimens and from a review of previously defined taxa. However, knowledge about many of these taxa remains relatively limited. We erect the new taxon, Larachelus morla, gen. et sp. nov., on the basis of a shell from the late Hauterivian–early Barremian of the Iberian Range (Spain). The comparative study of this taxon with the continental European Cretaceous pan-cryptodiran representatives and cladistic analyses reveal L. morla to be a member of the little-known European Early Cretaceous stem Cryptodira. Stem cryptodirans have been recognized from the Early Cretaceous of several continents. The study of L. morla not only confirms the presence of this group in the Early Cretaceous of Europe, it also provides new insights into the European evolution of Pan-Cryptodira. This finding reveals greater diversity in European Early Cretaceous continental pan-cryptodires, highlighting its Hauterivian–Aptian record. This diversity is particularly relevant in the Iberian Range, where several clades of turtles whose coexistence has not been recognized in the Lower Cretaceous of any other region are identified: paracryptodiran members, stem cryptodiran turtles, and representatives of several lineages of the crown group Cryptodira. This very high diversity of continental taxa shows a wide range of morphological diversity that could be related to adaptation to different ecological niches.

An explosive innovation: Phylogenetic relationships of Solanum section Gonatotrichum (Solanaceae)

Solanum is one of the largest plant genera and exhibits a wide range of morphological diversity. Solanum section Gonatotrichum, the focus of this study, is unique within the genus because of its fruits that swell with turgor pressure and explosively dehisce to disperse the seeds. We infer phylogenetic relationships within section Gonatotrichum using DNA sequence data from two nuclear regions (ITS and the granule-bound starch synthase gene [GBSSI or waxy]) and the chloroplast region trnT-F. The resulting phylogenetic trees support the monophyly of the section with the inclusion of Solanum lignescens, a species not previously thought to belong to the group due to the presence of stellate hairs. This inclusion of this species in section Gonatotrichum suggests that the simple, often geniculate hairs of species in the group may represent reduced stellate hairs. The presence of heterantherous flowers appears to be derived in the section, but this character is largely lost in Solanum parcistrigosum.

Skeletogenesis and sequence heterochrony in rodent evolution, with particular emphasis on the African striped mouse, Rhabdomys pumilio (Mammalia)

Data documenting skeletal development in rodents, the most species-rich ‘order’ of mammals, are at present restricted to a few model species, a shortcoming that hinders exploration of the morphological and ecological diversification of the group. In this study we provide the most comprehensive sampling of rodent ossification sequences to date, with the aim of exploring whether heterochrony is ubiquitous in rodent evolution at the onset of skeletal formation. The onset of ossification in 17 cranial elements and 24 postcranial elements was examined for eight muroid and caviomorph rodent species. New data are provided for two non-model species. For one of these, the African striped mouse, Rhabdomys pumilio, sampling was extended by studying 53 autopodial elements and examining intraspecific variation. The Parsimov method of studying sequence heterochrony was used to explore the role that changes in developmental timing play in early skeletal formation. Few heterochronies were found to diagnose the muroid and caviomorph clades, suggesting conserved patterning in skeletal development. Mechanisms leading to the generation of the wide range of morphological diversity encapsulated within Rodentia may be restricted to later periods in development than those studied in this work. Documentation of skeletogenesis in Rhabdomys indicates that intraspecifc variation in ossification sequence pattern is present, though not extensive. Our study suggests that sequence heterochrony is neither pivotal nor prevalent during early skeletal formation in rodents.

Genetic diversity of the African hexaploid species Solanum scabrum Mill. and Solanum nigrum L. (Solanaceae)

Two hexaploid species of Solanum sect. Solanum are present in Africa: Solanum scabrum and S. nigrum. Solanum scabrum is a widely cultivated species and is used as a leafy vegetable, as a source of medicine and as a source of ink dye. In previous studies a wide range of morphological diversity has been reported in this species and in some studies subspecies have been proposed. Subspecies are also recognized in S. nigrum. However, it has not been established whether or not the morphological differences are reflected at the genomic level. The present study applies AFLPs to study the genetic diversity in S. scabrum and its relationship to geographical provenance, morphological differences and the possible existence of subspecies within S. scabrum and S. nigrum. The data obtained were analyzed with cluster analysis (using UPGMA and NJ). The results indicate that the genetic variation within S. scabrum was higher within accessions than between accessions. Accessions did not cluster according to their geographical provenance, indicating that accessions from different geographical areas were not significantly different genetically. The clustering reflected neither morphological differences nor domestication status (cultivated or wild). The morphological differences exhibited by S. scabrum could be due to selection by farmers for different plant types. The AFLP derived clustering pattern did not segregate the subspecies recognized in S. scabrum and S. nigrum into separate subclusters.

SSR analysis of cultivated groundnut (Arachis hypogaea L.) germplasm resistant to rust and late leaf spot diseases

Cultivated groundnut (Arachis hypogaea L.) is an agronomically and economically important oilseed crop grown extensively throughout the semi-arid tropics of Asia, Africa and Latin America. Rust (Puccinia arachidis) and late leaf spot (LLS, Phaseoisariopsis personata) are among the major diseases causing significant yield loss in groundnut. The development of varieties with high levels of resistance has been constrained by adaptation of disease isolates to resistance sources and incomplete resistance in resistant sources. Despite the wide range of morphological diversity observed in the cultivated groundnut gene pool, molecular marker analyses have thus far been unable to detect a parallel level of genetic diversity. However, the recent development of simple sequence repeat (SSR) markers presents new opportunities for molecular diversity analysis of cultivate groundnut. The current study was conducted to identify diverse disease resistant germplasm for the development of mapping populations and for their introduction into breeding programs. Twenty-three SSRs were screened across 22 groundnut genotypes with differing levels of resistance to rust and LLS. Overall, 135 alleles across 23 loci were observed in the 22 genotypes screened. Twelve of the 23 SSRs (52%) showed a high level of polymorphism, with PIC values ≥0.5. This is the first report detecting such high levels of genetic polymorphism in cultivated groundnut. Multi-dimensional scaling and cluster analyses revealed three well-separated groups of genotypes. Locus by locus AMOVA and Kruskal–Wallis one-way ANOVA identified candidate SSR loci that may be valuable for mapping rust and LLS resistance. The molecular diversity analysis presented here provides valuable information for groundnut breeders designing strategies for incorporating and pyramiding rust and late leaf spot resistances and for molecular biologists wishing to create recombinant inbred line populations to map these traits.

The bHLH-PAS protein Spineless is necessary for the diversification of dendrite morphology of Drosophila dendritic arborization neurons

Dendrites exhibit a wide range of morphological diversity, and their arborization patterns are critical determinants of proper neural connectivity. How different neurons acquire their distinct dendritic branching patterns during development is not well understood. Here we report that Spineless (Ss), the Drosophila homolog of the mammalian aryl hydrocarbon (dioxin) receptor (Ahr), regulates dendrite diversity in the dendritic arborization (da) sensory neurons. In loss-of-function ss mutants, class I and II da neurons, which are normally characterized by their simple dendrite morphologies, elaborate more complex arbors, whereas the normally complex class III and IV da neurons develop simpler dendritic arbors. Consequently, different classes of da neurons elaborate dendrites with similar morphologies. In its control of dendritic diversity among da neurons, ss likely acts independently of its known cofactor tango and through a regulatory program distinct from those involving cut and abrupt. These findings suggest that one evolutionarily conserved role for Ahr in neuronal development concerns the diversification of dendrite morphology.

Comparative Developmental Genetics and the Evolution of Arthropod Body Plans

The arthropods display a wide range of morphological diversity, varying tagmosis, as well as other aspects of the body plan, such as appendage and cuticular morphology. Here we review the roles of developmental regulatory genes in the evolution of arthropod morphology, with an emphasis on what is known from morphologically diverse species. Examination of tagmatic evolution reveals that these changes have been accompanied by changes in the expression patterns of Hox genes. In contrast, review of the modifications to wing morphology seen in insects shows that these body plan changes have generally favored alterations in downstream target genes. These and other examples are used to discuss the evolutionary implications of comparative developmental genetic data.

Salivary gland tumours.

Salivary gland tumours are a relatively rare and morphologically diverse group of lesions. Although most clinicians and pathologists will have encountered the more common benign neoplasms, few have experience of the full range of salivary cancers, which are best managed in specialist centres. This review considers some current areas of difficulty and controversy in the diagnosis and management of these neoplasms. The classification of these lesions is complex, encompassing nearly 40 different entities, but precise classification and terminology is essential for an accurate diagnosis and for the allocation of tumours to prognostic groups. For many salivary tumours diagnosis is straightforward but the wide range of morphological diversity between and within tumour types means that a diagnosis may not be possible on small incisional biopsies and careful consideration of the clinical and pathological features together is essential. Although tumour grading is important and helpful, it is not an independent prognostic indicator and must be considered in the context of stage. Large malignancies tend to have a poor prognosis regardless of grade and even high-grade neoplasms may do well when they are small. A helpful guide to management of salivary cancers is the '4 cm rule'.