Chromosomal evolution in Pleurothallidinae (Orchidaceae: Epidendroideae) with an emphasis on the genus Acianthera: chromosome numbers and heterochromatin

In this study, we analysed chromosome number variation and chromomycin A₃/4′,6‐diamidino‐2‐phenylindole (CMA/DAPI) banding patterns in 48 species belonging to 12 genera of subtribe Pleurothallidinae (Orchidaceae) in order to understand the chromosome evolution based on recent phylogenetic hypotheses and taxonomic treatments. All species had small chromosomes, with numbers ranging from 2n = 20 in two Specklinia spp. to 2n = 80 in an unidentified Octomeria sp. In Acianthera, the most highly represented genus in this study, a great diversity of chromosome number and pattern of fluorescent bands was observed, showing heterochromatin accumulation in Acianthera section Sicariae subsection Pectinatae. Interspecific ascending and, mainly, descending dysploidy were the main mechanisms of chromosome number evolution in subtribe Pleurothallidinae. For Pleurothallidinae, x = 20 is suggested as the basic chromosome number, the same suggested for the related subtribe Laeliinae and for the whole tribe Epidendreae. The Brazilian species of the mega‐genus Stelis had chromosomes with small amounts of heterochromatin and chromosome numbers based on x₂ = 16. These are generally divergent from those reported for Andean and Meso‐American species, but in agreement with the monophyletic hypothesis proposed for Stelis spp. with a Brazilian Atlantic distribution. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 178 , 102–120.     

Evolutionary significance of hybridization in Onosma (Boraginaceae): analyses of stabilized hemisexual odd polyploids and recent sterile hybrids

Interspecific hybridization is an important evolutionary force promoting plant speciation. In the genus Onosma, one of three main evolutionary lineages presumably evolved by hybrid speciation. The assumed hybrid lineage (Heterotricha) consists of two species complexes with bimodal karyotypes containing different numbers of large (L) and small (S) chromosomes, the tetraploid Onosma pseudoarenaria (2n = 12 L + 14S) and the triploid Onosma arenaria (2n = 12 L + 8S). The latter represents a rare case of hemisexual, asymmetrically compensating allopolyploids. Representatives of the other two lineages of the genus, Haplotricha (2n = 12 L) and Asterotricha (2n = 14S), have been considered to be the ancestral taxa of O. pseudoarenaria and O. arenaria, although this has yet to be investigated critically. In the present study, we examined genetic [amplified fragment length polymorphism (AFLP), internal transcribed spacer (ITS) , and chloroplast (cp)DNA)], reproductive (pollen viability and seed production) and cytogenetic (chromosome counts, genome size assessment) patterns to resolve the hypothesized allopolyploid formations in the Heterotricha group, single or polytopic allopolyploid origins, as well as ongoing interspecific gene flow as one piece of evidence for understanding past hybrid speciation events in the genus. Discordant patterns in maternally inherited cpDNA (Heterotricha accessions bearing the haplotypes related to asterotrichous species) and the nuclear ITS and AFLP markers (Heterotricha clustering with haplotrichous Onosma fastigiata), as well as karyological features, support the hybrid origin of the stabilized Heterotricha lineage. Genetic variation that is both large and geographically correlated indicates multiple origins of Heterotricha allopolyploids or, less likely, a single origin with recurring introgression from the progenitor species. The nuclear markers and cytogenetic features also provide evidence for the ongoing hybridization between O. arenaria and Onosma echioides (2n = 14S), which gives rise to sterile triploids of 2n = 6 L + 15S. We contrast the two cases of triploids with LLS (hemisexual O. arenaria from the stabilized Heterotricha lineage) and LSS (recent sterile hybrids) karyotypes, which could help to understand the mechanisms ensuring the establishment and reproductive fitness of the odd allopolyploids in Onosma. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 112 , 89–107.     

New chromosome reports in the subtribes Diocleinae and Glycininae (Phaseoleae: Papilionoideae: Fabaceae)

The base chromosome number of x = 11 is the most probable in all the subtribes included in tribe Phaseoleae, although some aneuploid reduction is evident in Collaea and Galactia (Diocleinae) and chromosome duplications are seen in Amphicarpaea, Cologania and Glycine (Glycininae). The aims of this study were to improve the cytological knowledge of some species of Collaea and Galactia and to examine the anomalous counts reported for Calopogonium (Glycininae) and verify its taxonomic position. In addition, a molecular phylogeny was constructed using nuclear ribosomal DNA sequences (internal transcribed spacer region), and the chromosome number was optimized on the topology. In this work, the chromosome counts for Galactia lindenii, Galactia decumbens and Collaea cipoensis (all 2n = 20), and Calopogonium sericeum (2n = 22) are reported for the first time. The new reports for Galactia and Collaea species are in agreement with the chromosome number proposed for subtribe Diocleinae. The study rejects the concept of a cytologically anomalous Calopogonium and, based on the phylogenetic analysis, corroborates the position of this genus within subtribe Glycininae. The ancestral basic chromosome number of x = 11 proposed for Phaseoleae is in agreement with the evolutionary pathway of chromosome numbers analysed in this work. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 158 , 336–341.     

Towards resolving the systematics of Cerastium subsection Cerastium (Caryophyllaceae): a cytogenetic approach

Analyses of mitotic chromosome numbers and nuclear DNA content were performed for 39 populations of 17 perennial Cerastium taxa from south‐eastern Europe. The DNA content ranged from 2C = 2.43 to 8.78 pg, revealing four ploidy levels corresponding to 4x (2n = 36), 8x, 12x and 16x. High‐polyploid cytotypes with a greater range of ploidy (up to 2n = 144) occur mostly in the central mountainous parts of the Balkan Peninsula. The chromosome number was determined for the first time for C. dinaricum (2n = 36 + 1B), C. decalvans subsp. orbelicum (2n = 36), C. decalvans subsp. glutinosum (2n = 36), C. neoscardicum (2n = 144), C. malyi subsp. serpentini (2n = 144) and C. moesiacum s.s. (2n = 144). New chromosome counts were recorded for C. arvense subsp. strictum (2n = 108), C. banaticum subsp. kosaninii (2n = 36) and C. grandiflorum (2n = 36). For the first time, flow cytometry was used to estimate C values for six species (15 taxonomic entities). The intraspecific variation quotient of C values is high, ranging from 1.003 in C. malyi to 1.306 in C. decalvans subsp. decalvans. The variation in chromosome size among both tetra‐ and octoploid members of Cerastium is much more prominent than in most other angiosperm polyploid series. Significant genome downsizing after polyploidization was observed in some investigated taxa. Differences in ploidy levels and monoploid genome size values confirm the taxonomic status of C. decalvans subsp. glutinosum and C. decalvans subsp. leontopodium. The results obtained indicate a possible close relationship between C. banaticum and C. grandiflorum, but not C. arvense. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 182 , 205–224.     

New chromosome counts and evidence of polyploidy in Haageocereus and related genera in tribe Trichocereeae and other tribes of Cactaceae

Chromosome numbers for a total of 54 individuals representing 13 genera and 40 species of Cactaceae, mostly in tribe Trichocereeae, are reported. Five additional taxa examined belong to subfamily Opuntioideae and other tribes of Cactoideae (Browningieae, Pachycereeae, Notocacteae, and Cereeae). Among Trichocereeae, counts for 35 taxa in eight genera are reported, with half of these (17 species) for the genus Haageocereus. These are the first chromosome numbers reported for 36 of the 40 taxa examined, as well as the first counts for the genus Haageocereus. Both diploid and polyploid counts were obtained. Twenty nine species were diploid with 2n=2x=22. Polyploid counts were obtained from the genera Espostoa, Cleistocactus, Haageocereus, and Weberbauerocereus; we detected one triploid (2n=3x=33), nine tetraploids (2n=4x=44), one hexaploid (2n=6x=66), and three octoploids (2n=8x=88). In two cases, different counts were recorded for different individuals of the same species (Espostoa lanata, with 2n=22, 44, and 66; and Weberbauerocereus rauhii, with 2n=44 and 88). These are the first reported polyploid counts for Haageocereus, Cleistocactus, and Espostoa. Our counts support the hypothesis that polyploidy and hybridization have played prominent roles in the evolution of Haageocereus, Weberbauerocereus, and other Trichocereeae.     

CHROMOSOME NUMBERS IN PERITYLE AND RELATED GENERA (PERITYLANAE-COMPOSITAE)

Chromosome numbers are presented for 28 species of the genus Perityle, one putative inter-sectional hybrid, two species of Amauria, one species of Eutetras, and one species of Pericome. For Perityle, initial counts are recorded for 12 species of sect. Laphamia (n = 16, 17, 18, 36, ca. 102) and 11 species of sect. Perityle (n = 11, 12, 13, 16, 17, 18, 19, 34, 51). Chromosome numbers for the two species of Amauria (n = 18) are first reports for the genus. Including the current information, chromosome numbers have been recorded for 37 of the approximately 50 species recognized for Perityle. At least 24 taxa have numbers of n = 17, suggesting a base chromosome number of x = 17 for Perityle.     

Cytogenetic variability in genus odontocheila (Coleoptera,Cicindelidae): karyotypes,C-banding,NORs and localisation of ribosomal genes of O. confusa and O. nodicornis

Two species of Odontocheila, O. confusa and O. nodicornis, from the Neotropical Region were studied regarding their karyotypes, localisation and activity of ribosomal genes and C-banding. The species, although belonging to the same genus, have quite distinct karyotypes. O. confusa has 10 pairs of autosomes and a single sex chromosome mechanism of the XY/XX type, thus a diploid value of 2n = 22 in males and females. One aneuploid male with a diploid number of 2n = 20 and one male with three B chromosomes were found in a total of eight males studied. O. nodicornis has 17 autosomal pairs and also a single chromosome system but of the X0/XX type, thus a diploid value of 2n = 35 in males and 2n = 36 in females. Fluorescence in situ hybridisation (FISH) revealed the presence of rDNA clusters in two autosomes in both species in mitotic and meiotic figures. Silver staining of male interphase nuclei confirmed the FISH results and showed that all rDNA genes were active. C-banding analysis revealed the presence of constitutive heterochromatin in the centromeres of all chromosomes in the two species plus two pairs in O. nodicornis with terminal positive C-bands. These results are discussed from the cytogenetic and evolutionary point of view.     

Karyology of the genus Epidendrum (Orchidaceae: Laeliinae) with emphasis on subgenus Amphiglottium and chromosome number variability in Epidendrum secundum

Epidendrum is one of the largest Neotropical genera of Orchidaceae and comprises approximately 1500 species. Only 2.8% of these species have been studied cytologically, demonstrating chromosome numbers ranging from n = 12 in E. fulgens to n = 120 in E. cinnabarinum. The present work evaluated the evolution of the karyotypes of Epidendrum spp. based on data gathered from the literature and from analyses of the karyotypes of 16 Brazilian species (nine previously unpublished). The appearance of one karyotype with n = 12 with one larger chromosome pair in subgenus Amphiglottium appears to have occurred at the beginning of the divergence of this lineage, and x = 12 probably represents the basic number of this subgenus. Epidendrum secundum exhibits wide variation in chromosome numbers, with ten different cytotypes found in 22 Brazilian populations, seven of which were new counts: 2n = 30, 42, 50, 54, 56, 58 and 84. Most lineages of Epidendrum seem to have been secondarily derived from one ancestral stock with x = 20, as is seen in the majority of the present‐day representatives of the genus. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 172 , 329–344.     

Chromosome number variation and polyploidy in the genus Echinocereus (Cactaceae)

Analyses of meiotic and mitotic chromosomes were undertaken in 16 taxa of Echinocereus belonging to 12 species and all seven taxonomic sections (sensu Taylor). Chromosome numbers are reported for the first time for eight taxa, and previously published chromosome counts are confirmed for the remaining eight. Both diploid and polyploid counts were obtained. Eleven (69%) of the taxa surveyed were diploid (2n = 22); the five varieties of E. engelmannii were polyploid (2n = 44). Overall, chromosome counts are available for 23 of the 48 proposed species (sensu Taylor). Of these, 19 (82%) are diploid, and four (18%) are polyploid. Polyploid cytotypes are most common in the primitive sections, e.g., sections Erecti and Triglochidiatus, which suggests that polyploidy is probably a derived condition in Echinocereus. Polyploid taxa range from medium to high latitudes and elevations relative to the overall distribution of the genus. Polyploidy, hybridization, and cryptic chromosomal rearrangements are thought to be the major causes of the speciation events of the genus.     

Evolutionary trends in Iridaceae: new cytogenetic findings from the New World

With the present work, we aim to provide a better understanding of chromosome evolutionary trends among southern Brazilian species of Iridoideae. Chromosome numbers and genome sizes were determined for 21 and 22 species belonging to eight genera of Tigridieae and two genera of Trimezieae, respectively. The chromosome numbers of nine species belonging to five genera are reported here for the first time. Analyses of meiotic behaviour, tetrad normality and pollen viability in 14 species revealed regular meiosis and high meiotic indexes and pollen viability (> 90%). The chromosome data obtained here and compiled from the literature were plotted onto a phylogenetic framework to identify major events of chromosome rearrangements across the phylogenetic tree of Iridoideae. Following this approach, we propose that the ancestral base chromosome number for Iridoideae is x = 8 and that polyploidy and dysploidy events have occurred throughout evolution. Despite the variation in chromosome numbers observed in Tigridieae and Trimezieae, for these two tribes our data provide support for an ancestral base number of x = 7, largely conserved in Tigridieae, but a polyploidy event may have occurred prior to the diversification of Trimezieae, giving rise to a base number of x₂ = 14 (detected by maximum‐parsimony using haploid number and maximum likelihood). In Tigridieae, polyploid cytotypes were commonly observed (2x, 4x, 6x and 8x), whereas in Trimezieae, dysploidy seems to have been the most important event. This feature is reflected in the genome size, which varied greatly among species of Iridoideae, 4.2‐fold in Tigridieae and 1.5‐fold in Trimezieae. Although no clear difference was observed among the genome sizes of Tigridieae and Trimezieae, an important distinction was observed between these two tribes and Sisyrinchieae, with the latter possessing the smallest genome sizes in Iridoideae. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 177 , 27–49.     

Onosma maculata sp. nov. (Boraginaceae) from Iran

Onosma maculata Ranjbar & Almasi, a new Boraginaceae species endemic to Iran, is described and illustrated. The new species belongs to Onosma sect. Onosma subsect. Onosma. It is closely related to O. nervosa Riedl, but is easily distinguished by its spotted stem and peduncle (vs no spots), leaves 14–23 cm long (vs leaves 4–12 cm long), pedicel 5–15 mm long (vs pedicel 3–5 mm long), higher density of hairs, and glabrous nutlet (vs villous). Moreover, meiotic chromosome number and behavior were studied in two populations of the new species and it was found to be diploid with 2n = 2x = 16.     

The annual species ofAdonis (Ranunculaceae)—a polyploid complex

The five annual species ofAdonis L., sect.Adonis, growing in Israel, form a series of diploid, tetraploid and hexaploid species. Their somatic chromosome numbers are 2n = 16 inA. annua L.,A. dentata Del. andA. palaestina Boiss., 2n = 32 inA. microcarpa DC., 2n = 48 inA. aestivalis L.; counts forA. dentata, A. palaestina andA. microcarpa are new records. There are indications that alloploidization may have been involved in the process of speciation in sect.Adonis. A taxonomic survey of the 8 species of the section reveals that a higher ploidy level is usually combined with a larger distribution area.     

Cytogeography of European perennial species of Cyanus (Asteraceae)

To reveal the general cytogeographical pattern of Cyanus section Protocyanus in Europe, DNA ploidy and/or chromosome numbers were newly examined for 160 populations by flow cytometry (450 plants) and/or chromosome counting (30 plants). Furthermore, previously published karyological data were revised (236 records). Our analyses confirmed chromosome counts of 2n = 22 for all newly investigated samples of the C. triumfetti group (the records for C. semidecurrens and C. ternopoliensis are new), C. diospolitanus and C. achtarovii; 2n = 44 for C. montanus and C. mollis; and 2n = 20 for C. lingulatus, C. napulifer, C. nissanus, C. orbelicus, C. thirkei, C. tuberosus and C. velenovskyi. The chromosome count of 2n = 20 is the first report for C. epirotus. The cytotype 2n = 40 was newly recorded for the Crimean endemic C. fuscomarginatus and Calabrian and Greek populations of C. graminifolius. The cytotypes 2n = 20 and 2n = 40 were confirmed for C. pindicola. For the first time triploidy (2n～3x～30) was found in C. nissanus, C. thirkei and in a newly discovered hybrid, C. epirotus × C. graminifolius. Two contrasting ecogeographical patterns emerged: cytotypes derived from the base chromosome number x = 11 (2n = 22, 44) are widespread in northern latitudes and ecologically diverse, whereas cytotypes with x = 10 (2n = 20, 30, 40) are confined to mountains in southern Europe. In general, tetraploids have smaller ranges than diploids. The new combinations Cyanus section Protocyanus (Dobrocz.) Ol?avská comb. nov. and Cyanus ternopoliensis (Dobrocz.) Ol?avská comb. nov. are provided. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173 , 230–257.     

华南地区3种兔儿风属植物(菊科-帚菊木族)的细胞学研究

首次报道了华南地区兔儿风属(Ainsliaea DC.)(菊科-帚菊木族Asteraceae-Pertyeae)3种植物共4个居群的染色体数目和核型。其中长穗兔儿风(A.henryi Diels)的染色体数目为2n=24,核型公式为2n=16m+8sm;三脉兔儿风(A.trinervis Y.C.Tseng)的染色体数目为2n=26,核型公式为2n=16m+10sm;莲沱兔儿风(A.ramosa Hemsl.)2个居群的染色体数目均为2n=26,核型公式为2n=26=22m+4sm。所有居群的染色体由大到小逐渐变化,核型没有明显的二型性。这些结果表明兔儿风属植物确有x=12和x=13两个基数,其中x=13可能是该属的原始基数。     

Caryological analysis of South American species of Vernonia (Vernonieae,Asteraceae)

Abstract

In the present study 16 populations belonging to 13 species of the genus Vernonia Schreb. were examined cytologically. In total, six different chromosome numbers, which represent three basic numbers: x = 10, x = 16 and x = 17, were found. These results include the first chromosome number reports for the following four species: V. lanifera Cristóbal & Dematt. (2n = 2x = 32), V. membranacea Gardner (2n = 2x = 34), V. salzmannii DC. (2n = 2x = 20) and V. scabrifoliata Hieron. (2n = 2x = 128). Besides, a new chromosome number was found in V. saltensis Hieron. (2n = 2x = 32), for which only tetraploid populations have been previously recorded. The data obtained in this work, along with the information available from the literature, show that the genus Vernonia in South America is heterogeneous with basic chromosome numbers that range between x = 9 and x = 19. These numbers suggest that a combination of polyploidy and aneuploidy has played an important role in the evolution of the genus.     

THE CYTOTAXONOMY OF FILIPENDULA (ROSACEAE) AND ITS IMPLICATIONS

The genus Filipendula Mill. is generally separated from Spiraea L. in systematic keys on the basis of a single fruit character. In some taxonomic treatments of the Rosaceae, where subfamilies are used, this places the genera in separate subfamilies. Karyological studies can be useful in assaying the justifiability of such treatment and are needed because of serious discrepancies between previous reports of chromosome numbers and the recent textbook designation, on dubious grounds, of F. vulgaris as an example of a “permanent chromosome hybrid.” The results given in this paper show that x = 7 in this genus (compared with x = 9 in Spiraea) and the reasons for rejecting previous counts of 2n = 15 for F. vulgaris are presented. “Permanent chromosome hybridity” for this species is also rejected. The possibility that a cytotype with 2n = 16 may exist in the northern part of the range of F. ulmaria cannot be completely discounted, but positive evidence is presented for 2n = 14 in this species (even though 2n = 16 has been reported most frequently recently). The basic number 7 for Filipendula is in agreement with the placing of this genus in the subfamily Rosoideae even though the hereditary peculiarities (apomixis and permanent chromosome hybridity) shown by some other members of this subfamily are apparently not now needed to explain the cytological situation in Filipendula.     

Chromosome number and karyotype of Phaenospermateae and Duthieeae (Poaceae), with reference to their systematic implications

Recent molecular phylogenetic studies indicate that Phaenospermateae and Duthieeae are among the early diverging lineages of Pooideae and that they are closely related to each other. Here, we test this with cytotaxonomical data. The monotypic tribe Phaenospermateae, represented by Phaenosperma globosum, has a chromosome number of 2n = 2x = 24 and a fairly symmetric karyotype consisting of 22 median (m) and 2 submedian (sm) chromosomes varying in length between 1.8–3 μm. Duthieeae, represented by Duthiea brachypodium, Sinochasea trigyna, Stephanachne monandra and Stephanachne pappophorea, also share the chromosome number 2n = 2x = 24 and similar symmetric karyotypes with the chromosomes varying in length between 1.4–5 μm. Thus, the close relationship of Phaenospermateae and Duthieeae is corroborated.     

Chromosome evolution in pseudoxyrhophiine snakes from Madagascar: a wide range of karyotypic variability

In this first cytogenetic survey on the lamprophiid snake subfamily Pseudoxyrhophiinae, we studied the karyology of ten snake species belonging to seven genera from Madagascar (Compsophis, Leioheterodon, Liophidium, Lycodryas, Madagascarophis, Phisalixella and Thamnosophis) using standard and banding methods. Our results show a wide range of different karyotypes ranging from 2n = 34 to 2n = 46 elements (FN from 40 to 48), with nucleolus organizer regions (NORs) on one (plesiomorphic) or two (derived/apomorphic) microchromosome pairs, and W chromosome at early or advanced states of diversification from the Z chromosome. The observed W chromosome variations further support the most accepted hypothesis that W differentiation from the Z chromosome occurred by progressive steps. We also propose an evolutionary scenario for the observed high karyotype diversity in this group of snakes, suggesting that it is derived from a putative primitive pseudoxyrhophiine karyotype with 2n = 46, similar to that of Leioheterodon geayi, via a series of centric fusions and inversions among macrochromosomes and translocations of micro‐ either to micro‐ or to macrochromosomes. This primitive Pseudoxyrhophiinae karyotype might have derived from a putative Lamprophiidae ancestor with 2n = 48, by means of a translocation of a micro‐ to a macrochromosome. In turn, the karyotype of this lamprophiid common ancestor may have derived from the assumed primitive snake karyotype (2n = 36 chromosomes, with 16 biarmed macro‐ and 20 microchromosomes) by a series of centric fissions and one inversion. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 112 , 450–460.     

Ploidy in the alpine sedge Kobresia pygmaea (Cyperaceae) and related species: combined application of chromosome counts,new microsatellite markers and flow cytometry

Polyploidy is a fundamental mechanism in evolution, but is hard to detect in taxa with agmatoploidy or aneuploidy. We tested whether a combination of chromosome counting, microsatellite analyses and flow cytometric measurements represents a suitable approach for the detection of basic chromosome numbers and ploidy in Kobresia (Cyperaceae). Chromosome counting resulted in 2n = 64 for Kobresia pygmaea and K. cercostachys, 2n = 58 and 64 for K. myosuroides, and 2n = 72 for K. simpliciuscula. We characterized eight microsatellite loci for K. pygmaea, which gave a maximum of four alleles per individual. Cross‐species amplification was tested in 26 congeneric species and, on average, six of eight loci amplified successfully. Using flow cytometry, we confirmed tetraploidy in K. pygmaea. Basic chromosome numbers and ploidy were inferred from chromosome counts and the maximum number of alleles per locus. We consider the basic numbers as x = 16 and 18, with irregularities derived from agmatoploidy and aneuploidy. Across all Kobresia taxa, ploidy ranged from diploid up to heptaploid. The combination of chromosome counts and microsatellite analyses is an ideal method for the determination of basic chromosome numbers and for inferring ploidy, and flow cytometry is a suitable tool for the identification of deviating cytotypes. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 176 , 22–35.     

Low incidence of polyploids and high uniformity of karyotypes displayed by Delphinium (Ranunculaceae) in the Hengduan Mountains region of south‐west China

The chromosome numbers and morphology in 92 populations belonging to 49 species and three varieties in the genus Delphinium L. (Ranunculaceae), mostly from the Hengduan Mountains region of south‐west China, were studied. Forty seven species and three varieties were diploid, with 2n = 16, one species was tetraploid, with 2n = 32, and one species had diploid and tetraploid cytotypes. Three species had B chromosomes, representing the first time the occurrence of B chromosomes has been reported in the genus. The karyotypes of all the diploid species were quite uniform, commonly bimodal, and usually consisted of one pair of large median‐centromeric (m), one pair of large submedian‐centromeric (sm), five pairs of medium‐sized subterminal‐centromeric (st), and one pair of smaller sm (rarely st) chromosomes. The low incidence of polyploids in Delphinium from the Hengduan Mountains region indicates that polyploidy has played a minor role in the speciation of this highly diversified genus in the region. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 158 , 172–188.