Evolutionary Diversification of New Caledonian Araucaria

New Caledonia is a global biodiversity hotspot. Hypotheses for its biotic richness suggest either that the island is a ‘museum’ for an old Gondwana biota or alternatively it has developed following relatively recent long distance dispersal and in situ radiation. The conifer genus Araucaria (Araucariaceae) comprises 19 species globally with 13 endemic to this island. With a typically Gondwanan distribution, Araucaria is particularly well suited to testing alternative biogeographic hypotheses concerning the origins of New Caledonian biota. We derived phylogenetic estimates using 11 plastid and rDNA ITS2 sequence data for a complete sampling of Araucaria (including multiple accessions of each of the 13 New Caledonian Araucaria species). In addition, we developed a dataset comprising 4 plastid regions for a wider taxon sample to facilitate fossil based molecular dating. Following statistical analyses to identify a credible and internally consistent set of fossil constraints, divergence times estimated using a Bayesian relaxed clock approach were contrasted with geological scenarios to explore the biogeographic history of Araucaria. The phylogenetic data resolve relationships within Araucariaceae and among the main lineages in Araucaria, but provide limited resolution within the monophyletic New Caledonian species group. Divergence time estimates suggest a Late Cretaceous-Cenozoic radiation of extant Araucaria and a Neogene radiation of the New Caledonian lineage. A molecular timescale for the evolution of Araucariaceae supports a relatively recent radiation, and suggests that earlier (pre-Cenozoic) fossil types assigned to Araucaria may have affinities elsewhere in Araucariaceae. While additional data will be required to adequately resolve relationships among the New Caledonian species, their recent origin is consistent with overwater dispersal following Eocene emersion of New Caledonia but is too old to support a single dispersal from Australia to Norfolk Island for the radiation of the Pacific Araucaria sect. Eutacta clade.     

Nuclear DNA content in the polyploid complex Turnera ulmifolia (Turnera L., Passifloraceae)

Turnera ulmifolia constitutes a well-studied polyploid complex with allo- and autopolyploid species ranging from 2 to 8x. Flow cytometry was used to determine nuclear DNA content, and to estimate 2C- and 1Cx-values with the aim of analysing the genome size in Turnera in terms of polyploid speciation. The 2C-value and 1Cx-value were evaluated in 12 species of the T. ulmifolia complex. Nuclear DNA content was estimated by flow cytometry of nuclei stained with propidium iodide. The 2C DNA content ranged from 1.38 to 1.83?pg in diploids, from 2.67 to 3.96?pg in tetraploids, from 2.73 to 4.31?pg in hexaploids, and from 3.53 to 5.90?pg in octoploids. The 1Cx-value ranged from 0.44 to 0.99?pg. The Turnera ulmifolia complex showed an increase in total DNA content in the ploidy level, but not in the expected proportion. The general tendency indicated a decrease in the 1Cx-value with increasing chromosome number, with T. grandidentata 4x being an outstanding exception. The 1Cx-values in the allooctoploids T. aurelii and T. cuneiformis differed by 1.6-fold from each other, probably as a result of different evolutionary histories following divergence from the last common ancestor.     

Geographical gradients in the genome size variation of wild coffee trees (Coffea) native to Africa and Indian Ocean islands

The genus Coffea, mainly native to Africa and to the Indian Ocean islands (Mascarocoffea), accounts for 124 species. Genome size data are available for 23 African species. The aim of this study was to assess the genome size of 44 Mascarocoffea species and to investigate possible association with species geographic distribution, stomata traits, and species relationships. 2?C values were measured using flow cytometry. A lyophilization procedure for leaves was tested. The 2?C nuclear DNA content of Mascarocoffea species ranged from 0.96 to 1.41?pg. Coffea mauritiana and Coffea humblotiana have the smallest genomes and Coffea millotii has the largest. Mean 2?C DNA for Mascarocoffea and Africa is 1.19 and 1.43?pg, respectively. The overall DNA values corresponded to two partially overlapped normal distributions: one harboring species from east Africa Mascarocoffea, the other harboring species from west/central Africa. Plotted on a geographical map according to the native origin of species, these values showed a gradient in Madagascar and Africa. Genome sizes increased following a north to southeast gradient in Madagascar and an east to west gradient in Africa. None, or only weak correlations were noted between genome size and stomata parameters. Genetically close species could be highly distinctive in their genome size while divergent species could be similarly sized. The non-random geographic distribution and habitat of species, and the absence of correlation between genome size and genetic relationships, suggest that during Coffea genome evolution, both DNA content increase and/or decrease occurred independently in Africa and in the Indian Ocean Islands.     

Genome Size Evaluation in Tetraodontiform Fishes from the Neotropical Region

Smooth pufferfish of the family Tetraodontidae had become pure genomic models because of the remarkable compaction of their genome. This trait seems to be the result of DNA loss following its divergence from the sister family Diodontidae, which possess larger genomes. In this study, flow cytometry was used for estimate the genome size of four pufferfish species from the Neotropical region. Cytogenetic data and confocal microscopy were also used attempting to confirm relationships between DNA content and cytological parameters. The haploid genome size was 0.71?±?0.03 pg for Sphoeroides greeleyi, 0.34?±?0.01 pg for Sphoeroides spengleri, 0.82?±?0.03 pg for Sphoeroides testudineus (all Tetraodontidae), and 1.00?±?0.03 pg for Chilomycterus spinosus (Diodontidae). These differences are not related with ploidy level, because 46 chromosomes are considered basal for both families. The value for S. spengleri represents the smallest vertebrate genome reported to date. Since erythrocyte cell and nuclear sizes are strongly correlated with genome size, the variation in this last is considered under both adaptive and evolutionary perspectives.     

Characterization of nuclear microsatellites in New Caledonian Araucaria species

Thirteen of the world's 19 species of Araucaria are endemic to the Pacific Ocean island of New Caledonia. In order to investigate the evolutionary biological processes underlying the radiation of the genus on the island we have developed a set of nuclear microsatellite loci. Using a membrane enrichment procedure, five loci have been developed (four derived from A. subulata DNA and one from A. rulei DNA) which amplified in A. columnaris. PCR products of the expected size were also produced in a very limited sample of eight other New Caledonian Araucaria species tested.     

Karyological relationships among some South American species of Solanum (Solanaceae) based on fluorochrome banding and nuclear DNA amount

Fluorescent chromosome banding and measurements of nuclear DNA content by image cytometry of Feulgen-stained cells were performed in one sample each of eight diploid (2n?=?24) species of Solanum: S.?endoadenium, S.?argentinum, S.?pseudocapsicum, S.?atropurpureum, S.?elaeagnifolium, S.?sisymbriifolium, S.?chenopodioides, and S.?palustre. The species studied could be distinguished by heterochromatin amount, banding patterns, and genome size. They exhibited only GC-rich heterochromatin and showed a comparatively low heterochromatin amount (expressed as percentage of haplotype karyotype length), ranging from 2.10 in S.?argentinum to 8.37 in S.?chenopodioides. Genome size displayed significant variation between species, with 1C-values ranging from 0.75?pg (735?Mbp) in S.?palustre to 1.79?pg (1,754?Mbp) in S.?sisymbriifolium. No significant correlation between genome size and heterochromatin amount was observed, but intrachromosomal asymmetry index (A ₁) was negative and significantly correlated with heterochromatin amount. DNA content was positively and significantly correlated with karyotype length. DNA C-value distribution in the genus as well as karyotype affinities and relationships between species are discussed in relation to different infrageneric classifications of Solanum.     

Characterization of nuclear microsatellite loci in South American Araucariaceae species

The Araucariaceae family has only two species in South America: Araucaria angustifolia and Araucaria araucana. Both species are mainly used for timber and have been overexploited in the past. Currently, they are found as fragmented populations and are classified under the International Union for Conservation of Nature and Natural Resources (IUCN) guidelines as vulnerable species. Population fragmentation may seriously affect the genetic diversity of these two species of Araucariaceae and can consequently lead to decreased survival. To better understand the genetic structure of these South American Araucaria species, eight nuclear microsatellites are reported: six new microsatellites loci developed based on a membrane enrichment procedure and two microsatellites loci transferred from the related species, Araucaria cunninghamii.     

Genome size and environmental factors in the genus Pinus

Nuclear 1C DNA content in haploid megagametophyte tissue of 18 North American and one exotic Pinus species was determined using scanning microspectrophotometry. The nuclear DNA content in root meristematic cells of Zea mays L. ssp. mays, inbred line Va35 (4C = 10.31 pg) was used as a standard. DNA content measured by microspectrophotometry was verified using laser flow cytometry with two additional standards, Hordeum vulgare cv. Sultan (2C = 11.12 pg) and P. eldarica (2C = 47.30 pg). DNA values obtained by both methods were significantly correlated (r = 0.987). The 1C nuclear DNA content ranged from 21 pg to 31 pg. The ratio of DNA content in embryo tissue of P. eldarica to that in megagametophyte tissue was 1.72 by scanning microspectrophotometry and 1.74 by laser flow cytometry. To date, this is the most comprehensive data set available for North American Pinus species. Relationships between genome size of 18 North American Pinus species and climatic factors and indices of growth were investigated using regression and correlation analyses. Positive correlations were observed between nuclear DNA content and growth indices, minimum seed-bearing age, and seed dimensions. Strong negative correlations were observed between nuclear DNA content and two climatic factors, the lowest mean annual and monthly precipitation (excluding January) and the highest mean monthly spring air temperature. These correlations suggest that the large genome size and its variation in Pinus are adapted responses to the habitats of these species.     

Does complete plastid genome sequencing improve species discrimination and phylogenetic resolution in Araucaria?

Obtaining accurate phylogenies and effective species discrimination using a small standardized set of plastid genes is challenging in evolutionarily young lineages. Complete plastid genome sequencing offers an increasingly easy‐to‐access source of characters that helps address this. The usefulness of this approach, however, depends on the extent to which plastid haplotypes track morphological species boundaries. We have tested the power of complete plastid genomes to discriminate among multiple accessions of 11 of 13 New Caledonian Araucaria species, an evolutionarily young lineage where the standard DNA barcoding approach has so far failed and phylogenetic relationships have remained elusive. Additionally, 11 nuclear gene regions were Sanger sequenced for all accessions to ascertain the success of species discrimination using a moderate number of nuclear genes. Overall, fewer than half of the New Caledonian Araucaria species with multiple accessions were monophyletic in the plastid or nuclear trees. However, the plastid data retrieved a phylogeny with a higher resolution compared to any previously published tree of this clade and supported the monophyly of about twice as many species and nodes compared to the nuclear data set. Modest gains in discrimination thus are possible, but using complete plastid genomes or a small number of nuclear genes in DNA barcoding may not substantially raise species discriminatory power in many evolutionarily young lineages. The big challenge therefore remains to develop techniques that allow routine access to large numbers of nuclear markers scaleable to thousands of individuals from phylogenetically disparate sample sets.     

Genome size and genome evolution in diploid Triticeae species.

One of the intriguing issues concerning the dynamics of plant genomes is the occurrence of intraspecific variation in nuclear DNA amount. The aim of this work was to assess the ranges of intraspecific, interspecific, and intergeneric variation in nuclear DNA content of diploid species of the tribe Triticeae (Poaceae) and to examine the relation between life form or habitat and genome size. Altogether, 438 plants representing 272 lines that belong to 22 species were analyzed. Nuclear DNA content was estimated by flow cytometry. Very small intraspecific variation in DNA amount was found between lines of Triticeae diploid species collected from different habitats or between different morphs. In contrast to the constancy in nuclear DNA amount at the intraspecific level, there are significant differences in genome size between the various diploid species. Within the genus Aegilops, the 1C DNA amount ranged from 4.84 pg in A. caudata to 7.52 pg in A. sharonensis; among genera, the 1C DNA amount ranged from 4.18 pg in Heteranthelium piliferum to 9.45 pg in Secale montanum. No evidence was found for a smaller genome size in annual, self-pollinating species relative to perennial, cross-pollinating ones. Diploids that grow in the southern part of the group's distribution have larger genomes than those growing in other parts of the distribution. The contrast between the low variation at the intraspecific level and the high variation at the interspecific one suggests that changes in genome size originated in close temporal proximity to the speciation event, i.e., before, during, or immediately after it. The possible effects of sudden changes in genome size on speciation processes are discussed.     

Nuclear DNA amounts in pacific Crustacea

Nuclear DNA amounts have been determined for 42 species of crustaceans bringing the total number of species with known nuclear DNA content to over 70. Genome size in Crustacea varies over a 25-fold range with a modal value of 2 to 3 pg haploid being common in many groups. Both average genome size and the amount of variability among species are characteristic for certain groups. A trend towards small genomes is evident in advanced and specialized crustacean groups. Somatic polyploidy is a very pronounced feature of the Crustacea. The data suggest that evolution by polyploidy may be more common in crustaceans than earlier data had indicated. These features and the presence of very characteristic satellite fractions in the nuclear DNA recommend the Crustacea for further studies in evolutionary genetics.     

The systematic value of nuclear DNA content for all species of Narcissus L. (Amaryllidaceae)

The taxonomy of all species of Narcissus (Amaryllidaceae), an important horticultural crop, has not been investigated recently. As a new approach, genome size was determined by flow cytometry with propidium iodide from 375 accessions. The somatic nuclear DNA contents (2C) were shown to range from 14 to 38 pg for the diploids. Narcissus assoanus and N. gaditanus are, based on their nuclear DNA content, removed from section Apodanthi and placed in a new section Juncifolii. The different ploidy levels and species involved were entangled for N . “fernandesii” s.l. and a new allotetraploid form is named here. Section Pseudonarcissus was much more heterogeneous in nuclear DNA content than expected. Sixty-five accessions of N. pseudonarcissus possessed, with 23.7 pg, similar amounts of DNA. However, several species from this section were clearly distinctive in nuclear DNA content. It runs from the diploid N. primigenius with 21.7 pg to the also diploid N. nevadensis with 38.2 pg. Also N. abscissus and N. moleroi are with about 26 pg clearly different from N. pseudonarcissus. For the first time, in 11 accessions, hexaploidy was found in N. pseudonarcissus ssp. bicolor. A new section Nevadensis with 30–39 pg of nuclear DNA was split off from the section Pseudonarcissus with now 21–27 pg. A nonoploid N. dubius with 96.3 pg has by far the highest amount of nuclear DNA and can be calculated to have the highest ploidy ever reported in Narcisssus. The total number of Narcissus species was determined as 36, nine more than in Flora Europaea and they were divided up in two subgenera and 11 sections. Flow cytometry is shown to produce easily obtainable and original systematic data that lead to new insights. Genome size or C-value turns out to be one of the most salient features to define the status of the species in the genus Narcissus.     

DNA Content Variation and Its Significance in the Evolution of the Genus Micrasterias (Desmidiales,Streptophyta)

It is now clear that whole genome duplications have occurred in all eukaryotic evolutionary lineages, and that the vast majority of flowering plants have experienced polyploidisation in their evolutionary history. However, study of genome size variation in microalgae lags behind that of higher plants and seaweeds. In this study, we have addressed the question whether microalgal phylogeny is associated with DNA content variation in order to evaluate the evolutionary significance of polyploidy in the model genus Micrasterias. We applied flow-cytometric techniques of DNA quantification to microalgae and mapped the estimated DNA content along the phylogenetic tree. Correlations between DNA content and cell morphometric parameters were also tested using geometric morphometrics. In total, DNA content was successfully determined for 34 strains of the genus Micrasterias. The estimated absolute 2C nuclear DNA amount ranged from 2.1 to 64.7 pg; intraspecific variation being 17.4–30.7 pg in M. truncata and 32.0–64.7 pg in M. rotata. There were significant differences between DNA contents of related species. We found strong correlation between the absolute nuclear DNA content and chromosome numbers and significant positive correlation between the DNA content and both cell size and number of terminal lobes. Moreover, the results showed the importance of cell/life cycle studies for interpretation of DNA content measurements in microalgae.     

Genetic variation and conservation of Changnienia amoena, an endangered orchid endemic to China

Nuclear DNA content (2C) is used as a new criterion to investigate nearly all species of the genus Nerine Herb. The species have the same chromosome number (2n = 2x = 22), with the exception of three triploid plants found. The nuclear DNA content of the diploids, as measured by flow cytometry with propidium iodide, is demonstrated to range from 18.0–35.3 pg. This implies that the largest genome contains roughly 2 × 10¹⁰ more base pairs than the smallest. The species, arranged according to increasing genome size, fell apart in three groups if growth cycle and leaf width were also considered. A narrow-leafed, evergreen group with a DNA content between 18.0 and 24.6 pg contains thirteen species, a broad-leaved winter growing group with four species has a DNA content from 25.3–26.2 pg and a broad-leafed summer growing group has a DNA content of 26.8–35.3 pg and contains six species. If the presence of filament appendages and hairiness of the pedicels were also considered, the thirteen evergreen species could be further divided into a group without filament appendages or hairy pedicels with a DNA content of 18.0–18.7 pg. A second group without filament appendages but with hairy pedicels had a DNA content of 19.7–22.3 pg. And a third group with both filament appendages and hairy pedicels had a DNA content of 22.0–24.6 pg. The exception is N. marincowitzii that, despite a low DNA content and narrow leaves is summer growing. The broad-leafed group is further characterised by the absence of filament appendages and the absence of strongly hairy pedicels. The exception here is N. pusilla that, despite a high DNA content, has narrow leaves and minutely hairy pedicels. Nuclear DNA content as measured by flow cytometry is shown to be relevant to throw new light on the relationships between Nerine species.     

Quantification and characterization of nuclear genomes in commercial red seaweeds (Gracilariales) from the Philippines

Eight species of Gracilariaceae from the Philippines, representing the generaGracilaria, Gracilariopsis andHydropuntia, were investigated to quantify and characterize their nuclear genomes. DNA reassociation kinetics were used to determine nuclear genome organization and complexity in six of these species. Results indicate the presence of three second order components corresponding to fast, intermediate and slow fractions. Repetitive sequences varied from 13–74% and unique DNA ranged from 26–84%. Microspectrophotometry with the DNA-localizing fluorochrome DAPI was used to quantify nuclear DNA contents. Comparisons of mean nuclear DNA (I _f ) values to chicken erythrocytes (RBC) resulted in an estimate of 0.38–0.43 pg/2 C genomes for seven of the species investigated. Preliminary analyses of agar content and quality confirm the economic potential ofGracilaria firma, Gracilaria sp. 2 from Sorsogon andGracilariopsis bailinae. Nuclear genome profiles developed from data for genome size, organization and complexity are compared with data for agar quantity and quality. Gel quality and quantity do not appear to be correlated with either large repetitive fraction DNA or a high degree of genome complexity.Author for correspondence     

Flow cytometric measurement of nuclear DNA content inCapsicum (Solanaceae)

Nuclei were isolated from leaf tissue of differentCapsicum species and the relative fluorescence intensity was measured by flow cytometry after propidium iodide staining.Pisum sativum nuclei with known nuclear genome size (9.07 pg) were used as internal standard to determine nuclear DNA content of the samples in absolute units. The 2C DNA contents ranged between 7.65 pg inC. annuum and 9.72 pg inC. pubescens, and the general mean of the genus was 8.42 pg. These values correspond, respectively, to 1C genome size of 3.691 (C. annuum), 4.690 (C. pubescens) and 4.063 (general mean) Mbp. In general, white-flowered species proved to have less DNA, with the exception ofC. praetermissum, which displayed a 2C DNA content of 9.23 pg. It was possible to divide the studied species into three main groups according to their DNA content, and demonstrate differences in DNA content within two of the three species complexes established on the basis of morphological traits.     

Nuclear genome size variation in fleshy-fruited Neotropical Myrtaceae

In Myrtaceae, reports regarding the nuclear DNA content are scarce. The aim of this study is to present genome size data for fleshy-fruited Myrteae, and to test their relation with chromosome number and ploidy, the available data for cytoevolutionary studies in Myrtaceae. Thirty species out of ten genera were investigated for chromosome number and genome size using flow cytometry. Twenty-eight species were diploid with 2n = 2x = 22 and two species were tetraploid with 2n = 4x = 44. All genome sizes measured are new. Among the diploid species, a gradual and small variation in 2C-values (0.486 pg in Gomidesia schaueriana to 0.636 pg in Eugenia multicostata) was observed, whereas the tetraploid genomes of Psidium acutangulum and P. cattleianum had about twice as much DNA (1.053 and 1.167 pg, respectively). The total interspecific variation of C-values was 2.45-fold. The fleshy-fruited Myrteae have smaller holoploid genomes than the capsular-fruited Eucalypteae and Melaleuceae.     

Characterization of highly conserved microsatellite loci in Araucaria cunninghamii and related species

 Ten microsatellite loci are described in Araucaria cunninghamii, the first reported in the Araucariaceae. Eight were tested in sections Eutacta and Bunya, which diverged more than 200 MYA, and to the sister genus Agathis. Specific amplification products within the expected size range were obtained for six to eight loci in section Eutacta (depending on species), five loci in section Bunya and three loci in Agathis. Two of the loci (CRCAc1 and CRCAc2, both GA repeats) produced specific amplification products in all taxa, with orthology confirmed by sequence analysis. The repeats were perfect in all taxa. The flanking sequences were extremely conserved, with sequence divergence of 0% to 2.0% within Araucaria species and 2.9% to 7.5% between Araucaria and Agathis. These microsatellites represent some of the most conserved microsatellite loci reported in plants. This may be due to a low evolutionary rate in Araucariaceae genome or the loci may be closely associated with highly conserved, unreported genes. Received January 14, 2002; accepted June 14, 2002 Published online: February 4, 2003 Current address: The Centre for Identification and Diagnostics, School of Life Sciences, The University of Queensland, Brisbane 4072, Australia.     

Revisiting the DNA C-values of the genome size-standards used in plant flow cytometry to choose the "best primary standards"

Flow cytometry (FCM) techniques have enabled characterization of the genome size for various plant species. In order to measure the nuclear genome size of a species, reference standards with well-established DNA content are necessary. However, different 2C-values have been described for the same species used as reference standard. This fact has brought about inaccurate genome measurements, making relevant the establishment of optimal DNA reference standards for plant cytometric analyses. Our work revisited the genome size of Arabidopsis thaliana and other seven plant standards, which were denominated ??Dole?el??s standard set?? and have been widely used in plant DNA measurements. These eight plant standards were reassessed for a comparative measurement of their DNA content values, using each plant species as primary standard in a cascade-like manner, from A. thaliana to Allium cepa. The genome size values obtained here were compared to those reported in the literature by statistical analyses. As a result, Raphanus sativus and Drosophila melanogaster were considered the most inadequate primary standards, whereas A. thaliana, Solanum lycopersicum and Pisum sativum were found to be the most suitable.     

Genome size in Hieracium subgenus Hieracium (Asteraceae) is strongly correlated with major phylogenetic groups

Background and Aims

Hieracium subgenus Hieracium is one of the taxonomically most intricate groups of vascular plants, due to polyploidy and a diversity of breeeding systems (sexuality vs. apomixis). The aim of the present study was to analyse nuclear genome size in a phylogenetic framework and to assess relationships between genome size and ploidy, breeding system and selected ecogeographic features.

Methods

Holoploid and monoploid genome sizes (C- and Cx-values) of 215 cultivated plants from 89 field populations of 42 so-called ‘basic’ Hieracium species were determined using propidium iodide flow cytometry. Chromosome counts were available for all analysed plants, and all plants were tested experimentally for their mode of reproduction (sexuality vs. apomixis). For constructing molecular phylogenetic trees, the external transcribed spacer region of nuclear ribosomal DNA was used.

Key Results

The mean 2C values differed up to 2·37-fold among different species (from 7·03 pg in diploid to 16·67 in tetraploid accessions). The 1Cx values varied 1·22-fold (between 3·51 and 4·34 pg). Variation in 1Cx values between conspecific (species in a broad sense) accessions ranged from 0·24% to 7·2%. Little variation (not exceeding the approximate measurement inaccurracy threshold of 3·5%) was found in 33 species, whereas variation higher than 3·5% was detected in seven species. Most of the latter may have a polytopic origin. Mean 1Cx values of the three cytotypes (2n, 3n and 4n) differed significantly (average of 3·93 pg in diploids, 3·82 pg in triploids and 3·78 pg in tetraploids) indicating downsizing of genomes in polyploids. The pattern of genome size variation correlated well with two major phylogenetic clades which were composed of species with western or eastern European origin. The monoploid genome size in the ‘western’ species was significantly lower than in the ‘eastern’ ones. Correlation of genome size with latitude, altitude and selected ecological characters (light and temperature) was not significant. A longitudinal component was only apparent for the whole data set, but absent within the major lineages.

Conclusions

Phylogeny was the most important factor explaining the pattern of genome size variation in Hieracium sensu stricto, species of western European origin having significantly lower genome size in comparison with those of eastern European origin. Any correlation with ecogeographic variables, including longitude, was outweighed by the divergence of the genus into two major phylogenetic lineages.Key words: Apomixis, chromosome numbers, Compositae, genome size, hawkweeds, Hieracium subgenus Hieracium, mode of reproduction, nuclear DNA content, phylogeny, polyploidy