Apomixis in Taraxacum paludosum (section Palustria, Asteraceae): Recombinations of apomixis elements in inter-sectional crosses

Recent studies have shown independent control of apomixis elements (restitution/diplospory, parthenogenesis and autonomous endosperm) in Taraxacum sect. Ruderalia. We studied inheritance of apomixis elements in the section Palustria using the crosses between various sections used as mother plants and apomictic T. paludosum (sect. Palustria) as pollen donor. Non-apomictic plants prevailed in F₁ progeny, and a high incidence of sterility was observed. Triploid non-apomictic F₁ hybrids were backcrossed with diploids (sects. Ruderalia, Palustria) and tetraploids (sects. Palustria, Piesis), and produced various types of progeny. These F₁ hybrids were classified into three types depending on the occurrence of parthenogenesis along with restitution, and the occurrence of various progeny in particular crosses (i.e. within the same mother plant) was observed. The results indicate the independent genetic control of all apomixis elements in T. paludosum, and recombinations during a restitutional megasporogenesis in hybrids.     

New chromosome numbers inTaraxacum with reference to SAT-chromosomes

Chromosome numbers of eight agamospermousTaraxacum microspecies are reported for the first time:T hypanicum Tzvel. [sect.Dioszegia (Heuff.) Heuff.,T. neosivaschicum Tzvel. [sect.Palustria (Lindb, fil.)Dahlst.],T. pseudohoppeanum Kirschner et?těpánek (sect.Erythrocarpa Dahlst.),T. schroeterianum H.-M. (sect.Rhodocarpa Van Soest),T. marmottae C.E. Sonck,T. lambinonii Van Soest [sect.Erythrosperma (Lindb. fil.)Dahlst.],T. zermattense Dahlst, andT. magnoobliquum Van Soest (taxa of uncertain classification). All these polyploid microspecies have satellite chromosomes in their karyotypes. Advanced karyological characters were found in sect.Dioszegia, hitherto regarded as a primitive section ofTaraxacum: triploidy in agamospermousT. hypanicum Tzvel. and satellite chromosomes as in this taxon, as in two diploid sexualsT. serotinum (W. et K.)Poiret andT. haussknechtii Uechtr. The results presented are compared to the literature data.     

New sections in<Emphasis Type="Italic">Taraxacum</Emphasis>

Sectional taxonomy ofTaraxacum in steppe or subsaline habitats in Central Asia is revised based on material collected during expeditions, cultivated or studied in herbarium. Two new sections are described from that area:T. sect.Stenoloba similar toT. sect.Leucantha (syn.:T. sect.Sinensia), andT. sect.Suavia allied toT. sect.Dissecta. The type species of the sectionSuavia is described asTaraxacum formosissimum Kirschner etŠtěpánek. Widespread mountain dandelions of the Caucasus, intermediate between the sect.Piesis andT. stevenii, are described asT. sect.Confusa. Taraxacum species dominating dry habitats in S Ukraine and Crimea are described asT. sect.Borysthenica. Species belonging to the new sections were found to be polyploid and agamospermous.     

Twelve new native Taraxacum species from the Nordic countries

Eleven native Taraxacum species from Norden are described as new: T. acutilimbatum, T. frondatum, T. latulum, T. thorvaldii, T. wendtii and T. wessbergii (all in T. sect. Erythrosperma), T. danicum (sect. Palustria), T. conspersum and T. lentiginosum (sect. Naevosa), T. pietii‐oosterveldii (sect. Celtica) and T. ovillum (sect. Spectabilia). They are compared with morphologically similar species, and their ecological preferences are outlined. Known distribution areas and lists of paratypes are given. Taraxacum polyschistum Dahlst. forma oelandicum G. E. Haglund (sect. Erythrosperma) is given status of species.     

Towards a better understanding of the <Emphasis Type="Italic">Taraxacum</Emphasis> evolution (Compositae–Cichorieae) on the basis of nrDNA of sexually reproducing species

The genus Taraxacum is characterized by prevailing complex multiple hybridity, frequent polyploidy and widespread agamospermous reproduction, which makes the phylogenetic analysis difficult. On the basis of the previous analysis of the variation of nrDNA in Taraxacum taxa with different ploidy levels and modes of reproduction, to mitigate consequences of the reticulate complexity of the genus, a phylogenetic study of 52 samples of sexually reproducing dandelions of 26 sections (and another 13 agamospermous representatives of other sections known to include sexuals) was carried out. Both sexual and agamospermous samples were analysed using maximum parsimony and neighbour network. Exclusively sexual dandelions were analysed using the same approaches. In spite of the general agreement among various types of analyses, there is a limited overall congruence between results of nrDNA analyses and the established taxonomic system of the genus Taraxacum. The analyses shed light on the relationships among the most primitive groups. A stable clade is formed by representatives of the sections Primigenia, Orientalia, Sonchidium, Piesis and T. cylleneum. Another case of stable relationships is that of the members of the sect. Dioszegia. Relationships between the sects. Erythrosperma and Erythrocarpa were supported, and the relatedness of the members of sect. Australasica was confirmed. Rather unexpectedly, the agamospermous samples of the sect. Oligantha (T. minutilobum) are shown to be closely related with the sect. Macrocornuta. The latter section is generally considered to be close to sect. Ceratoidea (T. koksaghyz) on morphological grounds but this presumption is not corroborated by the results of nrDNA analyses. Analyses of 72 samples of sexual dandelions were also performed using the trnL–trnF region of the chloroplast DNA. The maximum parsimony analysis of this region reveals intraspecific variation in a number of ancestral diploid sexual species, all present in the two main branches of the cladogram. This phenomenon is attributed to the ancient gene flow and possibly to the persistence of ancestral cpDNA polymorphism. The strict consensus cpDNA tree information content and interpretability is quite low. The maximum parsimony analysis of combined nrDNA and cpDNA data sets was also performed with expectably low interpretability of the results.     

Taraxacum siphonanthum, a new species from Nei Mongol, Ne China

A new species,Taraxacum siphonanthum X.D.Sun, Ge Xuejun, Kirschner & Štěpánek is described from Nei Mongol, NE China. The species is intermediate between sectionsMongolica andBorealia, although in most characters it is closer to the former. It is an apomictic species with tubular florets; these and other similar characters inTaraxacum are discussed.     

Selected and annotated chromosome counts inTaraxacum sect.Palustria Dahlst. (Studies inTaraxacum 3.)

Chromosome counts of 9 species ofTaraxacum sect.Palustria are given. Five species were karyologically examined for the first time, viz.T. trilobifolium Hudziok,T. lissocarpum agg.,T. paucilobum Hudziok,T. subalpinum Hudziok andT. mendax, a new pentaploid species. Taxonomic and nomenclatural notes are added.     

Differentiation of Diploid and Triploid Taxa within Taraxacum sect. Erythrosperma (Asteraceae) from the Pannonian Region

Six taxa of the genus Taraxacum sect. Erythrosperma were analyzed morphometrically using multivariate methods. A total of 391 specimens from Slovakia, Hungary, Czech Republic and Austria were studied. This study aimed to explore if leaf shape can be used to differentiate diploids and triploids, to verify if triploid microspecies deserve separate taxonomic status, and if the diploid plants can be divided into phenotype groups. The analysis of leaf-shape variability revealed no notable difference between diploid and triploid plants. The analysis of the triploid microspecies T. cristatum, T. danubium, T. parnassicum, T. princeps and T. proximum s.l. resulted in their differentiation into separate groups. For differentiation, the characters with a higher determination value were employed, especially the shape of a terminal leaf lobe, the position of outer bracts, the number of lateral lobes and their termination. Analyzing a very variable diploid species T. erythrospermum enabled the definition of four basic phenotypes based on leaf shape. The phenotypes differed in leaf size and shape in relation to environmental factors such as intensity of light, nutrients, moisture, or disturbance. In conclusion, to evaluate the taxonomic status of particular taxa within Taraxacum sect. Erythrosperma it is inevitable to understand the complex leaf-shape variability, being a result of both genetic variability and phenotypic plasticity.     

The genusTaraxacum in the Caucasus 1. Introduction, 2. The sectionPorphyrantha

An introduction is presented to a taxonomic evaluation of rich cultivated and herbarium material of the genusTaraxacum from the Caucasus. Sources of the material, a survey of localities, and a preliminary account of the sections and species groups ofTaraxacum described from the Caucasus are given. The introduction is followed by a monograph ofT. sect.Porphyrantha, a section shown (contrary to the original conception and some literature data) to be endemic to the Caucasus. Six new species are described belonging to the section divided in two subsections, subsect.Porphyrantha and subsect.Haemantha, viz.T. pseudoporphyranthum, T. vepallidum, T. haemanthum, T. ignivomum, T. exstinctum andT. deminutum. Lectotypes are selected forT. porphyranthum Boiss. andT. pseudoroseum ?i?kin.     

Genome sizes of all 19 Araucaria species are correlated with their geographical distribution

Nuclear genome size was determined to investigate the relationships between all 19 species of Araucaria de Jussieu. Species from the two other genera of Araucariaceae, Wollemia and Agathis, were also studied. The genome size of 17 out of the 19 species of Araucaria are reported here for the first time. All Araucariaceae have the same chromosome number 2n?=?26. However, the nuclear DNA contents (2C value) for Araucaria range from 31.3 to 45.4?pg. There is a good correlation between genome size and division in sections, and geographical distribution. The two species from South America have 44.7 and 45.4?pg, the two species from Australia have 35.7 and 44.4?pg and the two species from New Guinea 34.7 and 40.4?pg. All 13 species of New Caledonia and the one from Norfolk Island have a similar, if not identical, amount of nuclear DNA of, on average, 31.9?pg. This corroborates the identical DNA rbcL sequences found for the New Caledonian araucarias. It suggests that the species from New Caledonia diversified more recently and it questions their status as separate species. Compared with this 31.9?pg a strong increase seems to have occurred in the genome size of the “mainland” araucarias. Genome sizes are evaluated and compared with available taxonomic treatments and extant geographic spreading. The nuclear DNA contents found within the sections are close, making it possible to assign an unknown plant to a section. A difference of 1?pg, which amounts to a difference of 978?Mbp, far exceeds a single character. Nuclear DNA content, as measured by flow cytometry, may conveniently be used to produce systematic data. It is applicable even with young plants or seeds for monitoring the trade in endangered species.     

Differentiation of the pollen size in five representatives of <Emphasis Type="Italic">Taraxacum</Emphasis> sect. <Emphasis Type="Italic">Palustria</Emphasis>

Measurements of the pollen size in 5 species of Taraxacum sect. Palustria at three levels of ploidy: 2n = 3x = 24 (T. paucilobum), 2n = 4x = 32 (T. vindobonense, T. trilobifolium), 2n = 5x = 40 (T. mendax) and one taxon of unknown number of chromosomes 2n = ? (T. portentosum) are presented in this paper. Obtained results indicate a lack of distinct positive correlation between the pollen size and ploidy in the studied group of plants. Distinct relationship was, however, found between ploidy and the range of pollen size and shape variability. Most variable were the pollen grains of triploid T. paucilobum and the least — those in pentaploid T. mendax. Ranges of pollen variability in tetraploid T. trilobifolium and T. vindobonense and in T. portentosum of unknown number of chromosomes showed intermediate values.     

Latitudinal variation in suppression of flower bud formation at high temperature in four native dandelions (Taraxacum spp.) with different distributions and genetic structures in Japan

The control of the response of flowering to temperature plays a key role in successful range‐expansion of plants. A previous study showed that the suppression of flower‐bud formation at high temperature in Taraxacum officinale decreases genetically with latitude from north to south in Japan. The present study investigated whether similar trait variation occurs among populations of native Taraxacum species in Japan. Seedlings of T. albidum (a low‐ and mid‐latitude allopolyploid), T. japonicum (a mid‐latitude diploid) and T. venustum (a high‐latitude autopolyploid) were grown at three temperatures. Time to flower‐bud appearance increased with temperature in T. japonicum and T. venustum, but did not increase in T. albidum. Time to flower‐bud appearance did not differ significantly among the three species at 14°C, but it was shorter in T. albidum than in the other two species at 19°C and 24°C. The early appearance of buds of T. albidum was confirmed by another experiment in which plants of 18 populations from the three species and T. platycarpum (a mid‐latitude diploid) grown at 19°C were used. The results clearly indicate that high‐temperature suppression of flower‐bud formation was lower in low‐latitude species than in high‐latitude species. This interspecific variation is analogous to the intraspecific variation in T. officinale. Time to bud appearance of five populations in T. albidum was homogeneous within and between the populations. The results suggest that the five populations are monoclonal and lack the sensitivity of suppression of flower‐bud formation to high temperature.     

Photonastic and thermonastic opening of capitulum in dandelion,Taraxacum officinale andTaraxacum japonicum

The capitula ofTaraxacum officinale andT. japonicum open in response to temperature rise at lower temperatures (thermonasty), and in response to light at higher temperatures (photonasty), as was the case inT. albidum. The capitula ofT. officinale could respond to the same temperature rise more sensitively than those ofT. albidum orT. japonicum. The minimum temperature for photonastic opening is as low as 13 C forT. officinale, while that forT. albidum andT. japonicum is about 18 C. That is why the capitula ofT. officinale opened earlier than those ofT. albidum andT. japonicum in the morning in April under natural conditions. The capitulum continued to be open for about 13–14 hr inT. officinale and about 8–11 hr inT. japonicum and inT. albidum both under natural conditions in April and even under constant light-temperature conditions, suggesting that the time of capitula-closing in these three species is not controlled by changes in environmental factors (light and/or temperature).     

Variation inTaraxacum bessarabicum and allied taxa of the sectionPiesis (Compositae): allozyme diversity,karyotypes and breeding behaviour

Allozyme techniques, karyotype analyses and cultivation experiments were carried out on 20 population samples ofTaraxacum sect.Piesis (Compositae), viz.T. bessarabicum (17 samples from W. and C. Europe, Ukraine and Crimea, Central Asia and the Altai),T. salsum from Crimea,T. x mesohalobium from Crimea, andT. stenolepium from the Causasus. The taxa studied share a primitive, symmetrical karyotype. All taxa studied are sexual,T. bessarabicum mostly autogamous. Sexuality at the tetraploid level (T. stenolepium) and occasional male sterility in a sexual (T. bessarabicum in Moravia) were recorded for the first time in the genus. Selfing, diploidy and the highly predictable habitat may account for the mostly low level within population allozyme variation inT. bessarabicum. W. and C. European samples ofT. bessarabicum are almost invariable allozymically and, as a group, have no unique alleles. The Crimean and Asian group of populations shows higher levels of allozyme variation and has 15 alleles not found in the former group at 13 loci studied. Recent migration from one source region is suggested to account for the homogeneity of the western group, refugial persistence of alleles and possible introgression from sympatric species may have resulted in allele richness in the eastern group. Hybridization betweenT. bessarabicum andT. salsum was documented by allozyme patterns in a few plants in Crimea. Some aberrant allozyme or karyotypic features of two populations are discussed as well.     

Anthropogenic disturbance and habitat differentiation between sexual diploid and apomictic triploidTaraxacum sect.Ruderalia

Co-occurrence of sexual diploid and apomictic triploidTaraxacum sectionRuderalia has been reported frequently. Many suggestions have been put forward with respect to the existence of an ecological differentiation between the cytotypes. In a study of 116Ruderalia populations in the area around Neuchatel (Switzerland) such a habitat differentiation has been proven. Large differences in the diploid/triploid ratio have been found between different field types. Adjacent fields of different types sometimes had significantly different cytotype ratios. In a canonical correspondence analysis significant vegetation differences were found between fields with mainly diploidRuderalia and fields with mainly triploidRuderalia. Two environmental indicators were significantly positively correlated with ploidy levels, altitude with diploids, and the percentage of therophytes in a vegetation with triploids. The percentage of therophytes is thought to be an indicator of the amount of disturbance due to human activities. At lower altitudes, the diploid/triploid ratio is largely determined by the amount of disturbance. Highly-disturbed fields contain mainly triploids whereas relatively stable fields contain mainly diploids. At higher altitudes there are mainly diploids. The presence of triploidTaraxacum sect.Ruderalia in the region around Neuchatel appears to be the result of the high amount of human activities of the last few hundred years. Whether the triploid presence is due to immigration or to local formation from diploids is yet unknown.     

A trnL-F based phylogeny for species ofPelargonium (Geraniaceae) with small chromosomes

Phylogenetic analysis was performed of 921 positions of trnL (UAA) 5 exon — trnF (GAA) exon chloroplast DNA regions from 68 representatives ofPelargonium sectt.Campylia, Cortusina, Glaucophyllum, Hoarea, Isopetalum, Ligularia, Otidia, Pelargonium, Peristera, Polyactium, andReniformia, together with five putative outgroup species from sectionsCiconium, Chorisma andJenkinsonia. The total data set therefore comprised 67.2 kb of DNA sequence. Two main ingroup clades were identified: one clade contains sectionsPeristera, Reniformia, andIsopetalum, the other contains sectionsCampylia, Cortusina, Glaucophyllum, Hoarea, Ligularia, Otidia, Pelargonium, Polyactium and two species currently grouped in sect.Peristera. Branching order among five main clades within the latter clade was not resolved. The trnL-F sequence data support monophyly only for sectionsReniformia andHoarea, the remainder of the currently recognized sections ofPelargonium being either paraphyletic or polyphyletic. The data further suggest that sect.Polyactium is diphyletic and that sect.Glaucophyllum is nested within sect.Pelargonium. One relatively derived clade, which represents half of the genus, contains predominantly geophytic and succulent species, occurring in the geographically restricted winter rainfall region of the South African Cape. This pattern is interpreted as reflecting explosive radiation, possibly as an adaptive response to recent aridification in the western Cape.     

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.     

Genetic interpretation of enzyme variation in sexual and agamospermous taxa of Taraxacum sections Vulgaria and Mongolica

The inheritance of 15 enzymes, comprising at least 22 genetic loci, was investigated in crosses between sexual diploid individuals of Taraxacum sections Vulgaria and Mongolica. Patterns were consistent with simple Mendelian segregation. From the inheritance information isozyme phenotypes in agamospermous plants from natural populations were inferred. In some crosses part or all of the progeny originated from self-fertilization, sofar a very rare phenomenon in the sections Vulgaria and Mongolica. It is possible that the probability of self-fertilization increases after pollination by triploid pollen, affecting the cohabitation dynamics of the various ploidy components in mixed natural stands.