Low Chromosome Number Research Articles

Meiosis in Haematopinus Suis and Menacanthus Stramineus (Phthiraptera, Insecta)

Haemalopinus suis (Anoplura) and Menacanthus stramineus (Mallophaga) have been cytogenetically analyzed. Both species have 2n = 10, holokinetic chromosomes, and achiasmatic male meiosis. Bivalents orientate with their long axis perpendicular to the spindle fibers at melaphase I, and first anaphase is reductional. As in other species of Phthiraptera, male gametogenesis follows a particular pattern: each cell entering meiosis results in a cyst of 64 (in H. suis) and 32 (in M. stramineus) spermatozoa and 64/32 non-functional cells (=pycnotic nuclei). The results are compared with those previously reported for Phthiraptera, and a new terminology for the different stages of male gametogenesis is proposed. The low chromosome number together with the achiasmatic nature of male meiosis and the mitotic divisions that follow meiosis may restrict the potential for genetic variability. This might be related to the high host specificity of these parasites.

Cytogenetics of a Moth Species with a Low Chromosome Number, Orgyia Thyellina

While most Lepidoptera have numerous small chromosomes, Orgyia thyellina has few (n = 11) and relatively big chromosomes. We exploited this situation in a light microscopic study of chromosome morphology in mitosis and in various stages of male and female meiosis.—There is no indication of a primary constriction in mitotic chromosomes. Meiosis is chiasmatic in males and achiasmatic in females. Bivalents in the late female pachytene stage have a chromomere pattern of an unusually high degree of resolution. It is especially suited to test structural homology of synapsed chromosomes in bivalents. The chromomere pattern is homologous in the synapsed autosomes but partly differential in the equally synapsed sex chromosomes. The female pachytene affords a good basis for cytogenetic investigations in Lepidoptera.

Karyotype Evolution by Chromosome Fusion in the Moth Genus Orgyia

Chromosome numbers vary greatly in Orgyiu, from low numbers, like n = 11 in O.thyellina and n = 14 in O.antiqua, to a high number, n = 30, as in O.recens and O. ericue. Meiotic synapsis was regular in O. thyellina and O.antiqua; 11 and 14 normal bivalents, respectively, were found in meiosis. The paired homologues displayed homologous chromomere patterns. In the species hybrid between antiqua and thyellina, many synapsed chromosome segments were found in meiosis. This indicates sufficient segmental homology between chromosomes of the two species although the paired pachytene chromosome segments rarely displayed similar chromomere patterns. Chromosomes switched pairing partners, thus forming multivalents, linked by chiasmata in males, and long synaptic chains in the achiasmatic females. Multivalent formation is understood as the consequence of a separate evolution of the two species from a species with a high chromosome number. Multiple chromosome fusions resulted in similarly low chromosome numbers but different segmental compositions of the chromosomes in the two species.

Identification of RAPD markers linked to recessive genes conferring siliqua shatter resistance in Brassica rapa

AbstractShattering of siliquae causes significant seed loss in canola (Brassica napus) production worldwide. There is little genetic variation for resistance to shatter in canola and, hence, the trait has been studied in B. rapa. Previous studies have shown two randomly segregating recessive genes to be responsible for shatter resistance. Three random amplified polymorphic DNA markers were identified as being linked to shatter resistance using bulked segregant analysis in a F3B. rapa population. The population was derived from a cross between a shatter‐susceptible Canadian cultivar and a shatter‐resistant Indian line. Of the three markers, RAC‐3900 and RX‐71000 were linked to recessive sh1 and sh2 alleles, and SAC‐201300 was linked to both dominant Sh1 and Sh2 alleles. The common marker for the dominant wild‐type allele for the two loci was explained to have resulted from duplication of an original locus and the associated markers through chromosome duplication and rearrangements in the process of evolution of the modern B. rapa from its progenitor that had a lower number of chromosomes. Segregation data from double heterozygous F3 families, although limited, indicated the markers were not linked to each other and provided further evidence for the duplication hypothesis.

Uniparental loss of ribosomal DNA in the allotetraploid grass Zingeria trichopoda (2n = 8).

Analysis of the grass Zingeria trichopoda (2n = 8, 2C = 5.3 pg) revealed a dynamic evolution with the following characteristics. (i) Genomic in situ hybridization (GISH) demonstrates that Z. trichopoda evolved from an interspecific hybrid involving a species like contemporary Zingeria biebersteiniana (2n = 4) and a second species with a similar low number of chromosomes. The nucleus of Z. trichopoda is spatially organized at the genome level and the two parental genomes occupy distinct and separate domains of lateral arrangements. (ii) The copy number of the Z. biebersteiniana specific pericentromeric tandem repeat family Zbcen1 is drastically reduced in Z. trichopoda. (iii) GISH in combination with labeled rDNA sequences simultaneously discriminated the two parental genomes and the corresponding 5S and 45S rDNA sites. Hence, following allopolyploidization of Z. trichopoda the Z. biebersteiniana like parental chromosomes probably underwent drastic loss of 45S rDNA. This could have arisen either through the loss of Z. biebersteiniana derived 45S rDNA or through Z. trichopoda genome-wide homogenization of Z. biebersteiniana type 45S rDNA and subsequent elimination of 45S rDNA loci from Z. biebersteiniana derived chromosomes. Finally, 5S rDNA loci are present in both subgenomes of Z. trichopoda and the chromosomal position of these loci is similar for both Z. biebersteiniana and the Z. biebersteiniana like parental genome of Z. trichopoda.

Reversal and convergence in marsupial chromosome evolution

The karyotypes of marsupial species are characterized by their relatively low number of chromosomes, and their conservation. Most species have diploid numbers lying between the two modes, 2n = 14 and 2n = 22, but the karyotype of Aepyprymnus rufescens is exceptional in containing 2n = 32 chromosomes. Many differences in diploid number between marsupial species can be accounted for by particular fissions and fusions, which are easy to detect because of the low numbers of chromosomes in each karyotype. This should be a system in which it is possible to detect reversals and repeated chromosome rearrangements. We have used chromosome-specific paints derived from A. rufescens to compare the karyotypes of eight marsupial species, representing closely and distantly related taxa, to trace chromosome change during evolution, and especially to detect reversals and convergence. From these and other painting comparisons, we conclude that there have been at least three reversals of fusions by fissions, and at least three fusions or fissions that have occurred independently in different lineages.

Review of chromophobe renal cell carcinoma with focus on clinical and pathobiological aspects.

In recent years, the concept of chromophobe renal cell carcinoma (RCC) has been established. Chromophobe RCCs account for about 4-6% of all renal tumors. Macroscopically, the cut surface of the tumor is generally grey-beige in color. Histologically, there are two variants (typical and eosinophilic). In the typical variant, large tumor cells with architecture of a compact tubulo-cystic pattern proliferate. The cytoplasm is abundant and shows a fine reticular translucent pattern. The cell border is thick, prominent and eosinophilic. In the eosinophilic variant, tumor cells are smaller and markedly eosinophilic, and a perinuclear halo is often seen. Histochemically, the tumor cells generally show a diffuse and strong reaction for Hale's colloidal iron staining. Ultrastructurally, tumor cells contain many cytoplasmic microvesicles (150-300 nm). In chromosomal analysis, a low chromosome number is characteristic of chromophobe RCCs, due to the frequent occurrence of a combined loss of chromosomes 1, 2, 6, 10, 13, 17, and 21. In differential diagnosis, histological distinction from oncocytomas, which share a common phenotype (intercalated cells of the collecting duct system), is most important. In this diagnostic setting, recent studies have given rise to several problems. Firstly, some cases of coexistent chromophobe RCC and oncocytoma (so-called renal oncocytosis) or cases of oncocytoma with metastasis have recently been reported. Secondly, the existence of chromophobe adenoma, which is the benign counterpart of chromophobe RCC, and an oncocytic variant of chromophobe RCC has recently been suggested. Therefore, further studies are needed to elucidate the relationship between chromophobe RCCs and oncocytomas, to confirm whether chromophobe adenoma actually exists or not, and to identify the key gene that causes chromophobe RCCs.

An unusual karyotype with low chromosome number in Megacephalini, a basal group of tiger beetles (Coleoptera, Cicindelidae): cytogenetic characterisation by C-banding and location of rDNA genes

Mitotic and meiotic chromosomes of Megacephala brasiliensis, a representative of the tribe Megacephalini-a basal group in the family Cicindelidae-were studied using conventional Giemsa-staining, C-banding and fluorescence in-situ hybridization (FISH) with 18S rDNA probe. The diploid chromosome number was 2n=12 and the karyotype contained five pairs of metacentric and submetacentric autosomes and one pair of sex chromosomes, XY and XX in male and female, respectively. The X chromosome was metacentric while the Y was subtelocentric. All autosomes and the X showed distinct, large C-positive blocks around the centromere indicating extensive distribution of constitutive heterochromatin. The Y chromosome showed a conspicuous large C-positive block in the subterminal region as well as a weak interstitial band. FISH with a rDNA probe gave consistently positive signals in the pericentromeric region of the fourth pair of chromosomes. Size polymorphism of this rDNA-positive site was always observed. The karyotype of this beetle exhibits the smallest 2n known for any tiger beetle of the genus Megacephala and of other basal groups of the family though it shares single sex chromosome system with them. The extreme reduction in the autosome number appears to be the result of massive and combined rearrangenments of various types. The discovered case might parallel the famous “Muntjac scandal” in mammal cytogenetics.

First chromosome number determinations in south-eastern South American species of Lupinus L. (Leguminosae)

Chromosome numbers are presented for the first time for 30 accessions of nine south-eastern South American Lupinus species. Chromosome numbers of 2n = 32 and 34 were found for L. bracteolaris (three out of five accessions with 2n = 32) and L. linearis (two out of three accessions with 2n = 32), and of 2n = 36 for L. gibertianus, L. lanatus, L. magnistipulatus, L. multiflorus, L. rubriflorus, L. reitzii and L. uleanus. All the South American species examined have relatively low chromosome numbers when compared with most of the Old World and North American species. Our results, where 2n = 36 is the rule, are in sharp contrast to the data for North American Lupinus species and reveal the following: (1) low chromosome numbers are the rule, at least in the southern part of eastern South America; (2) cytologically, the eastern South American species form a group distinct from the North American taxa; (3) high levels of polyploidy have not played as important a role in evolution and speciation in eastern South America as in North America; (4) the predominance of low chromosome numbers in eastern South American species and the existence of similar numbers in two of the six rough-seeded Old World species support the hypothesis that in the evolution of the genus the eastern South American species branched off first, followed by the rough-seeded group. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Socety, 2002, 139, 395–400.

The Taxonomy of the Carex bicknellii Group (Cyperaceae) and New Species for Central North America

Based on morphology and karyology, we found the eastern North American species Carex bicknellii (sect. Ovales) to be a complex of four spe- cies. We describe two new species, C. missouriensis and C. shinnersii, and raise one variety, C. bicknellii var. opaca, to species rank as C. opaca. The three species segregated from C. bicknellii have lower chromosome numbers: n = 23 II + 1 III to 27 II for C. missouriensis, n = 29 II + 1 III to 30 II for C. shinnersii, and n = 32 II + 1 III to 34 II for C. opaca. All three species are characterized by large tussocks, herbaceous textured foliage and smooth sheaths, and long apiculum on the achenes; they occupy hydric habitats. Carex missouriensis, a spe- cies characterized by awned pistillate scales, grows in remnant prairie swales from western Indiana to southeastern Nebraska. Carex opaca, with blunt scales and large perigynia, has a narrow distribu- tion mostly limited to the periphery of the Ozark Mountain system. Carex shinnersii, with acuminate but unawned scales and perigynia smaller than C. opaca and C. missouriensis, ranges from northern Texas to southern Kansas. This last species is also contrasted with C. brevior, a species with similar morphology and overlapping range. Carex bicknellii in the strict sense is morphologically similar to the northeastern species C. merritt-fernaldii. They both have few culms per tussock, coriaceous foliage with papillose sheaths, papery, erose-margined perigyn- ia, achenes with a very short apiculum, and rela- tively high chromosome numbers (n = 35 II to 39 II). These two species differ in characters of the anther, achene, and perigynium. They occupy more or less xeric habitats, especially in the Central Plains of the United States (C. bicknellii) and south- ern Canada eastward from the Great Lakes region

Origin and relationships of the tarweed–silversword lineage (Compositae–Madiinae)

Based on results from phylogenetic analyses of nuclear 18S-26S rDNA internal transcribed spacer (ITS) region sequences, we suggest that the monophyletic tarweed and silversword subtribe (Madiinae) is phylogenetically nested among epaleate, x = 19 species of helenioid Heliantheae. Strong bootstrap support (100%) was obtained for a sister-group relationship between Madiinae and Arnica (including Mallotopus and Whitneya) in an analysis including representatives of recognized genera in a principally Californian clade (Madieae sensu Baldwin) identified from a phylogenetic investigation of Heliantheae s.l. (sensu lato) and Eupatorieae. In all minimum-length trees, the robust lineage comprising Madiinae and Arnica (x = 19) is part of a larger clade that also comprises Eatonella s.s. (sensu stricto), Hulsea, and Venegasia, all with x = 19. The phylogenetic position of Madiinae within a group of genera based uniformly on x = 19 leads us to conclude that the modal numbers of n = 7 and n = 8 (and other numbers, as low as n = 4) in Madiinae are the results of extreme dysploidy. Among the x = 19 "arnicoid" taxa, the near-universal characteristics of perenniality (except in the monotypic Eatonella s.s. and a minority of hulseas) and montane or high-latitudinal occurrence (except in the monotypic Venegasia) lead us to suggest that the most recent common ancestor of the tarweeds (a principally annual group of seasonally dry, low-elevation habitats) was probably a montane, herbaceous perennial resembling the unusual subalpine and alpine tarweeds constituting Raillardella s.s. (x = 17), an arnica-like genus. In Madiinae, Raillardella s.s. may be plesiomorphic in habit, capitular and ecological characteristics, and high base chromosome number. Shifts to an annual habit and to low chromosome numbers in Madiinae have been followed by subsequent episodes of polyploidy and descending dysploidy. We conclude that genome evolution in Madiinae has been marked by wide swings in chromosome number that confuse identification of diploids and polyploids.

Estudios cromosómicos en Vernonia cincta y V. scorpioides (Asteraceae- Vernonieae)

Vernonia cincta Griseb. y V. seorpioides V. (Lam.) Pers.. (Asteraceae, Vernonieae) son dos taxones estrechamente relacionados que han sido considerados por diferentes autores como una misma especie o como dos variedades de la misma especie. En el presente estudio se realizó un detallado análisis cromosómico en un intento de aclarar la situación y las relaciones de estos dos taxones. El estudio citológico reveló que Vernonia cincta tiene 2n = 60 cromosomas y una fórmula cariotípica compuesta de 36m + 16sm + 8t, mientras que V. scorpioides presenta 2n = 66 y un cariotipo con 34m + 20sm + 12t. Además, V. cincta mostró dos pares de cromosomas con satélite en los brazos cortos, un par m con satélite lineal y un par t con macrosatélite; mientras V. scorpioides presentó un par de cromosomas m que llevaba un satélite lineal en el brazo largo. Además del número de cromosomas, estas especies mostraron algunas otras diferencias de cariotipo, principalmente en su fórmula, la longitud cromosómica total y el nivel de asimetría. La información cromosómica aquí presentada apoya el estatus específico de ambos taxones. La presencia de cromosomas telocéntricos en V. cincta y V. scorpioides los distinguen del resto de las especies de Vernonia del Nuevo Mundo, que suelen tener cromosomas metacéntricos y submetacéntricos. Las diferencias en el cariotipo de V. cincta y V. scorpioides puede explicarse por la ocurrencia de rearreglos estructurales, tales como fusiones céntricas o traslocaciones. Esta hipótesis está sostenida por la similitud en la longitud total del cariotipo en ambos taxones y la mayor de longitud promedio de los cromosoma de V cincta, que presenta un menor número de cromosomas telocéntricos que V. seorpioides.

In vitro Regeneration and Cytological Studies on Somaclones ofErianthus elephantinus Hook. F.

Callus induction, plantlet regeneration and their field establishment were achieved in the genusErianthus which is closely related toSaccharum. The species utilised wasE. elephantinus with the lowest chromosome number of the genus (2n = 20). The donor clone SES 305 is cytologically stable. The 64 somaclones which attained maturity and were studied did not show much morphological variation. However, many somaclones showed consistantly low pollen fertility over years. Although chromosome numerical variation was rare structural aberrations such as occurrence of a fragment, chromosome fusion, ring chromosomes, laggards, bridges etc. were noticed during root tip mitosis and meiosis. The data did not indicate any relationship between pollen fertility and meiotic abnormalities.

Strinatia brevipennis Chopard 1970 and S. teresopolis sp. n.: Description of New Species and Comparative Study of Their Chromosomes and Male and Female Genitalia Sclerites (Grylloidea, Phalangopsidae)

Materials and Methods A new species of the genus Strinatia Chopard is described. The new species differs from S. brevipennis Chopard, the only other known species of the genus, in body color pattern, chromosome number and the structure of the male and female genitalia sclerites. Strinatia shows affinities with Eidmanacris-they both have low chromosome numbers, a reduction of the tegmina to small pads, and the absence of tibial tympanum. However, they differ in the size of the stylet, which is very short in Strinatia and elongated in Eidmanacris species, and in the shape of the distal ectophallic sclerites. [

Use of FISH Analysis for Diagnosis of Renal Cell Carcinoma Subtypes

Cytogenetic and molecular genetic techniques have been used in demonstrating the chromosomal abnormalities which characterize specific subtypes of renal cell carcinoma (RCC). The aim of this study was to determine the efficiency of fluorescent in situ hybridization (FISH) technique in characterizing various subtypes of RCC based on the presence of specific chromosome abnormalities found in each RCC subtype. FISH was performed on touch imprint smears from eight renal cell carcinomas histologically confirmed by established criteria. In four tumors with histologic features of chromophobe renal cell carcinoma (ChRCC), interphase FISH was performed using centromeric probes for chromosomes 1, 2, 6, 10, 12, 17 and 21. All four ChRCC tumors showed one FISH signal corresponding to one copy number for each of these chromosomes. Two papillary RCCs included in this study showed trisomy 7 and 17, and loss of chromosome Y, using the corresponding chromosome centromeric probes. Similarly, we tested two clear cell RCCs for chromosome 3 short arm deletion with DNA probe 3p21.3. Both tumors showed loss of 3p21.3 signal. We conclude that interphase FISH performed on touch imprint smears is a relatively simple, rapid and reliable method for detecting chromosome abnormalities which are specific for various subtypes of RCC.

Molecular genetics and diagnosis of renal cell tumors

Renal cell tumors display notoriously an intra- and intertumoral morphological heterogeneity making a reproducible cytomorphological diagnosis impossible. To overcome the cytological heterogeneity, the "Heidelberg Classification of Renal Cell Tumours" is soundly based on the genetic lesions that underlie the formation of distinct tumors. Allelic loss of chromosome 3 p and mutation of the VHL gene specify conventional renal cell carcinoma. In addition duplication of chromosome 5 q as well as allelic losses of prognostic value at chromosomes 6 q, 8 p, 9 p and 14 q characterize conventional renal cell carcinomas. Papillary renal cell tumors, which display an adenoma-carcinoma sequence, are marked by trisomies of chromosomes 3 q, 7, 8 p, 12 q, 16 q, 17 q und 20 as well as loss of the Y chromosome in males. Chromophobe renal cell carcinoma shows a low chromosome number due to monosomy of chromosomes 1, 2, 6, 10, 13, 17, and 21. Benign tumors, such as renal oncocytoma and metanephric adenoma, can also be diagnosed by genetic means. The distinct types of tumors have different biological behaviour and therefore, an accurate classification is considered clinically important. We worked out a quick and reproducible fluorescent microsatellite assay for detecting allelic changes. This technique is useful for postoperative and retrospective diagnosis as well as for preoperative analysis of fine needle aspiration specimens.

Molecular Systematics of the Asteriscus Alliance (Asteraceae: Inuleae) I: Evidence from the Internal Transcribed Spacers of Nuclear Ribosomal DNA

The Asteriscus alliance comprises three genera (Asteriscus, Ighermia, and Pallenis) restricted to Macaronesia and the Mediterranean basin. This alliance is a member of the tribe Inuleae where it forms a distinct morphological group with low chromosome numbers (n = 5-7). The taxonomic boundaries of the three genera have been controversial, although previous morphological cladistic analyses support the monophyly of each genus. Phylogenetic comparisons of most taxa in the alliance and seven other genera of Inuleae were conducted using ITS sequences. Parsimony analyses support the monophyly of the Asteriscus alliance and identify four lineages. One group has two species (P hierochuntica and P maritima), and two lineages are monotypic (P spinosa and A. aquaticus). The fourth lineage includes the remaining 10 taxa of the Asteriscus alliance. Neither Asteriscus nor Pallenis, as currently defined, is monophyletic, and Ighermia is sister to the largest Asteriscus clade. All taxa distributed in Macaronesia, the arid African-Mediterranean basin, the Sahara region, and the Middle East (except P hierochuntica) are part of the largest lineage. At least two independent colonizations from northern Africa have occurred in Macaronesia, one involving A. schultzii and the second including the remaining five taxa endemic to the Cape Verde and the Canary Islands. The derived position of these endemics in the ITS tree suggests a recent colonization of the Macaronesian Islands from northern Africa. The ITS phylogeny is incongruent with previous morphological cladograms of the Inuleae because Buphthalmum and Xerolekia are not sister to the Asteriscus alliance. Several genera have their center of species diversity in a geographical zone defined by the Iberian peninsula, Morocco and Macaronesia. This area has a rich flora with at least 3,000 endemic species (Bramwell 1972; Quezel 1978, 1985; Gomez-Campo and Malato-Beliz 1985; Gomez-Campo et al. 1984; Greuter 1991; La Roche and Rodriguez-Pifiero 1994; Medail and Quezel 1997). The isolation of the 32 Macaronesian Islands and the existence of a high number of ecological niches in mountain ranges such as the Sierra Nevada in southern Spain and the Atlas systems of Morocco have facilitated the explosion of biodiversity in these regions (Greuter 1991; Medail and Quezel 1997). Major climatological changes of the late Tertiary were less dramatic in these regions and many organisms may have found refuge in this area (Axelrod 1975; Axelrod and Raven 1978; Quezel 1978; Bramwell 1985). Fur-

Post-zygotic gametic selection due to endosperm balance number explains unusual chromosome numbers of 3� � 2� progeny in Solanum

Crosses between triploid and diploid genotypes are usually the best sources of trisomics in potato as well as in several other crop species. However, 3×× 2× crosses between triploid (2n=3×=36; 2EBN) Solanum commersonii-S. tuberosum hybrids and diploid (2n= 2×=24; 2EBN) genotypes gave progenies with a high number of extra chromosomes, 29–36, suggesting that only eggs with 17–24 chromosomes produced embryos that reached full development. Our hypothesis is that although triploids produce eggs with a range of chromosome numbers, 3×× 2× crosses involving a 2×(2EBN) parent favor eggs with a high chromosome number. These eggs have higher probabilities of possessing the same endosperm balance number (EBN) value (i.e. 1) of gametes produced by the 2EBN diploid parent to give the required 2:1 maternal to paternal EBN ratio in the hybrid endosperm. Under this model, trisomics are produced only if the diploid parent has an EBN of 1. Based on our results and those reported in the literature, it is proposed that in 3×(2EBN) × 2×(2EBN) crosses the endosperm balance number exercises negative selection for gametes with a low chromosome number, and a corresponding low EBN, and positive selection for gametes with a high chromosome number and EBN.

Cytotaxonomic studies of Encarsia Förster (Hymenoptera: Aphelinidae)

AbstractA cytotaxonomic study was carried out on 13 species of Encarsia Förster, known to parasitize aleyrodids and diaspidids. The chromosomes varied greatly both in number and morphology, with E. protransvena Viggiani having the lowest chromosome number (2n = 6) and E. asterobemisiae Viggiani & Mazzone the highest (2n = 20). The most common chromosome number was 2n = 10. C-banding, G-banding and silver staining for nucleolar organizer regions (NOR) provided the possibility of distinguishing between karyotypes with the same chromosome number and morphology and to identify all the pairs of homologues in a diploid set for advanced cytogenetic studies. The karyotype of Coccophagus lycimnia (Walker) was also examined. The chromosome data suggested that in Encarsia, karyotype differentiation has mainly occurred through a series of centric fusions, although other rearrangements may also have been significant. The importance of karyological data in systematic studies and in the identification of biotypes and cryptic species of economic interest is outlined.

Molecular phylogeny ofBrachycome (Asteraceae)

Intrageneric relationships in the genusBrachycome were investigated by the comparison of nucleotide sequences of the chloroplast genematK. Evolutionary trends of some morphological and cytological characters were estimated based on thematK tree. The results indicate thatBrachycome is divided into four major clades, and circumscription of superspecies based primarily on fruit morphology is not fully supported. Fruit morphology has evolved in parallel from simple to complex structures in several lineages. The ancestral basic chromosome number isx = 9, and lower chromosome numbers are the products of several dysploid reductions fromn = 9 in two of four major clades ofBrachycome.