Karyotype evolution in apomictic Boechera and the origin of the aberrant chromosomes

Chromosome rearrangements may result in both decrease and increase of chromosome numbers. Here we have used comparative chromosome painting (CCP) to reconstruct the pathways of descending and ascending dysploidy in the genus Boechera (tribe Boechereae, Brassicaceae). We describe the origin and structure of three Boechera genomes and establish the origin of the previously described aberrant Het and Del chromosomes found in Boechera apomicts with euploid (2n = 14) and aneuploid (2n = 15) chromosome number. CCP analysis allowed us to reconstruct the origin of seven chromosomes in sexual B. stricta and apomictic B. divaricarpa from the ancestral karyotype (n = 8) of Brassicaceae lineage I. Whereas three chromosomes (BS4, BS6, and BS7) retained their ancestral structure, five chromosomes were reshuffled by reciprocal translocations to form chromosomes BS1‐BS3 and BS5. The reduction of the chromosome number (from x = 8 to x = 7) was accomplished through the inactivation of a paleocentromere on chromosome BS5. In apomictic 2n = 14 plants, CCP identifies the largely heterochromatic chromosome (Het) being one of the BS1 homologues with the expansion of pericentromeric heterochromatin. In apomictic B. polyantha (2n = 15), the Het has undergone a centric fission resulting in two smaller chromosomes – the submetacentric Het′ and telocentric Del. Here we show that new chromosomes can be formed by a centric fission and can be fixed in populations due to the apomictic mode of reproduction.     

Production of tetraploid plants of non apomictic citrus genotypes

Ploidy manipulation in Citrus is a major issue of current breeding programs aiming to develop triploid seedless mandarins to address consumer demands for seedless fruits. The most effective method to obtain triploid hybrids is to pollinate tetraploid non apomictic cultivars with pollen of diploid varieties. Such non apomictic tetraploid lines are not found in the citrus germplasm and need to be created. In this work we describe a new methodology based on in vitro shoot-tip grafting combined with treatment of the micro-grafted shoot-tip with colchicine and oryzalin to achieve chromosome doubling and a dechimerization procedure assisted by flow cytometry. Stable tetraploid plants of Clemenules, Fina and Marisol clementines and Moncada mandarin have been obtained directly from shoot tip grafting combined with colchicine and oryzalin treatments or after dechimerization of mixoploids plants (2x–4x). These stable tetraploid plants have been used in 4x × 2x hybridizations, to recover over 3,250 triploid hybrids in 3 years.     

GEOGRAPHY OF CLAYTONIA VIRGINICA CYTOTYPES

Three widespread ploidy levels have evolved in Claytonia virginica, a diploid represented by n = 8, 7, and 6 races, a triploid primarily by n = 12 and 11, and a tetraploid by n = 16, 15, 14, and other aneutetraploids. In addition, sporadic higher polyploids (5x–24x) occur throughout eastern North America. These data are considered briefly in relation to meiotic behavior, to coexistence of major cytotypes, and to speciation.     

Genome accumulation in eastern gamagrass,Tripsacum dactyloides (L.) L. (Poaceae)

Intermatings between sexual diploids (2n=36) and facultative apomictic tetraploids (2n=4n=72) of Tripsacum dactyloides var. dactyloides, (L.), L., have been generated. Subsequent exchange and addition of genetic material between the two cytotypes, via a backcrossing program, provides one method for the manipulation of genetic elements involved in apomictic reproduction (diplospory) of this species.Identification and development of fertile triploids, and their innate tendency to exhibit a high frequency of unreduced egg cells which remain receptive to fertilization by a sperm nucleus, allows for the unique development of B _III (2n=3x+n) tetraploids by genome accumulation. The resultant B _III progeny provide new breeding stock for investigating the inheritance and generation of such materials also allows for the occurrence of genetic recombination between sexual diploids and apomictic tetraploids. Potential use of fertile triploids, their tendency for genome accumulation and their use in exploiting apomictic tetraploid germplasm resources are also discussed.All programs and services of the U.S. Department of Agriculture are offered on a nondiscriminatory basis without regard to race, color, national origin, religion, sex, age, marital status, or handicap.     

CHROMOSOME NUMBERS OF CAMPANULACEAE. III. REVIEW AND INTEGRATION OF DATA FOR SUBFAMILY LOBELIOIDEAE

Chromosome numbers are now known for 153 species in 21 genera of Lobelioideae (Campanulaceae); this represents almost 13% of the species and 70% of the genera in the subfamily. Numbers reported are n = 6, 7, 8, 9, 10, 11, 12, 13, 14, 19, 21, 35, 70. The subfamily as a whole has x = 7; the best documented exception is Downingia and its allies with x = 11. Only four genera show interspecific variation in chromosome number: Downingia (n = 6, 8, 9, 10, 11, 12); Lobelia (n = 6, 7, 9, 12, 13, 14, 19, 21); Pralia (n = 6, 7, 13, 14, 21, 35, 70); and Solenopsis (n = 11, 14). Intraspecific variation occurs in 13 species, with as many as four different cytotypes in one species. The herbaceous members of the subfamily as a group are quite variable, showing the entire range of chromosome numbers, including numerous dysploids, but are predominantly diploid. The woody species, by contrast, are much less variable; nearly all of the species are tetraploid, with only a few diploids and hexaploids and no dysploid numbers known. These data support the hypothesis that woodiness is apomorphic within the subfamily. A general trend of higher chromosome numbers at higher latitudes and higher elevations is evident within the subfamily. The chromosome number of Apetahia raiateensis (n = 14) is reported here for the first time, on the basis of a count made about 30 years ago by Peter Raven.     

Asynchronous meiotic rhythm as the cause of selective chromosome elimination in an interspecific <Emphasis Type="Italic">Brachiaria</Emphasis> hybrid

This paper reports the occurrence of chromosome elimination during microsporogenesis in an interspecific hybrid between a sexual diploid accession (SEX) of Brachiaria ruziziensis (2n=2x=18) and an apomictic tetraploid accession (APO) of B. brizantha (2n=4x=36). Meiosis was very abnormal in the triploid hybrid (2n=3x=27); we observed a distinct asynchrony from metaphase I to the end of meiosis. The APO and the SEX genomes did not show the same meiotic rhythm. When the former, with nine bivalents, was in metaphase I, the nine SEX univalents were not yet aligned; when the latter reached the plate, the APO genome was already in anaphase. In subsequent stages, the APO genome had reached the poles while the SEX was undergoing sister-chromatid segregation. As the SEX genome always remained temporally behind, it gave rise to one extra-nucleus in each pole. In the second division, the behavior was the same but anaphase II did not occur for the SEX genome, and only one extra-nucleus was observed in each cell in telophase II. Chromosome elimination for the SEX genome ranged from partial to total. The importance of these findings with respect to Brachiaria breeding programmes is discussed.     

Distribution and diversity of cytotypes in Dianthus broteri as evidenced by genome size variations

Background and Aims

Studying the spatial distribution of cytotypes and genome size in plants can provide valuable information about the evolution of polyploid complexes. Here, the spatial distribution of cytological races and the amount of DNA in Dianthus broteri, an Iberian carnation with several ploidy levels, is investigated.

Methods

Sample chromosome counts and flow cytometry (using propidium iodide) were used to determine overall genome size (2C value) and ploidy level in 244 individuals of 25 populations. Both fresh and dried samples were investigated. Differences in 2C and 1Cx values among ploidy levels within biogeographical provinces were tested using ANOVA. Geographical correlations of genome size were also explored.

Key Results

Extensive variation in chromosomes numbers (2n = 2x = 30, 2n = 4x = 60, 2n = 6x = 90 and 2n = 12x =180) was detected, and the dodecaploid cytotype is reported for the first time in this genus. As regards cytotype distribution, six populations were diploid, 11 were tetraploid, three were hexaploid and five were dodecaploid. Except for one diploid population containing some triploid plants (2n = 45), the remaining populations showed a single cytotype. Diploids appeared in two disjunct areas (south-east and south-west), and so did tetraploids (although with a considerably wider geographic range). Dehydrated leaf samples provided reliable measurements of DNA content. Genome size varied significantly among some cytotypes, and also extensively within diploid (up to 1·17-fold) and tetraploid (1·22-fold) populations. Nevertheless, variations were not straightforwardly congruent with ecology and geographical distribution.

Conclusions

Dianthus broteri shows the highest diversity of cytotypes known to date in the genus Dianthus. Moreover, some cytotypes present remarkable internal genome size variation. The evolution of the complex is discussed in terms of autopolyploidy, with primary and secondary contact zones.     

CHROMOSOME ANALYSIS OF HYBRIDS BETWEEN 4N GRINDELIA CAMPORUM AND 2N G. GRANDIFLORA (COMPOSITAE)

Morphology and meiosis are described in four progeny plants resulting from tetraploid Grindelia camporum Greene (2n = 24) from California pollinated by diploid G. grandiflora Hook. (2n = 12) from Coahuila, Mexico. Three of the four progeny were tetraploid, morphologically like the pistillate parent, and had metaphase I chromosome configurations which included quadrivalents and a complementary number of bivalents. They are considered to have resulted from selfing. The fourth plant was triploid (2n = 18) andmorphologically intermediate between the parents. Chromosome configurations in the triploid were variable with univalents, ring and rod bivalents, trivalents and pentavalents. These two species are considered related through an ancestor with a basic genome, but are separated cytologically by polyploidy and by two distinct chromosomal interchanges that explain the configurations observed in the triploid hybrid.     

Intraspecific genome size variation and morphological differentiation of Ranunculus parnassifolius (Ranunculaceae), an Alpine–Pyrenean–Cantabrian polyploid group

The aim of this study was to assess genome size variation and multivariate morphometric analyses to ascertain cytotype distribution patterns and the morphological differentiation within the Ranunculus parnassifolius group in the Pyrenees and the Alps. Although divergences in nuclear DNA content among different species within a genus are widely acknowledged, intraspecific variation is still a somewhat controversial issue. Holoploid and monoploid genome sizes (C‐ and Cx‐values) were determined using propidium iodide flow cytometry in 125 plants of R. parnassifolius s.l. distributed across four European countries. Three different DNA ploidy levels were revealed in the study area: diploid (2n ～ 2x, 57.14%), triploid (2n ～ 3x, 1.19%), and tetraploid (2n ～ 4x, 41.67%). The mean population 2C‐values ranged from 8.15 pg in diploids to 14.80 pg in tetraploids, representing a ratio of 1 : 1.8. Marked intraspecific/interpopulation differences in nuclear DNA content were found. Diploid populations prevail in the Pyrenees, although tetraploid cytotypes were reported throughout the distribution area. In general, mixed‐cytotype populations were not found. The Spearman correlation coefficient did not reveal significant correlations between genome size and altitude, longitude, or latitude. Morphometric analyses and cluster analyses based on genome size variation revealed the presence of three major groups, which exhibited a particular biogeographical pattern. A new cytotype, DNA triploid, was found for the first time. Tetraploid populations showed constant nuclear DNA levels, whereas diploid populations from the Pyrenees, in which introgressive hybridization is suggested as a presumable trigger for genome size variation, did not. Scenarios for the evolution of geographical parthenogenesis in R. parnassifolius s.l. are discussed. Finally, the different levels of effectiveness between plant and animal reference standards are analysed. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 251–271.     

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.     

AUTOPOLYPLOIDY IN TOLMIEA MENZIESII (SAXIFRAGACEAE)

Tolmiea menziesii comprises diploid (2n = 14) and tetraploid (2n = 28) cytotypes that differ in geographic distribution. Chromosome counts now available indicate that the diploid and tetraploid cytotypes occupy the southern and northern portions, respectively, of the range of Tolmiea. Available data strongly suggest that Tolmiea represents an example of autopolyploidy. The genus is monotypic and very distinct in both floral and vegetative morphology among genera of tribe Saxifrageae. Infraspecific taxa have not been recognized in T. menziesii, and the two cytotypes appear to be indistinguishable morphologically. Karyotypic, flavonoid chemical, and preliminary allozymic data are all in agreement with the contention that the tetraploid cytotype is of autopolyploidal origin.     

Karyomorphology and evolution in some Hamamelidaceae and Platanaceae (Hamamelididae; Hamamelidales)

Karyomorphology in 14 species of 12 genera representing a variation of Hamamelidaceae and in one species of Platanaceae (Platanus only) is investigated in an effort to contribute to an understanding of chromosome evolution and inter- and intrafamilial relationships. All genera investigated show similar chromosome features at resting stage and prophase, excepting that at resting stageRhodoleia shows the simple, rather than the simple-complex, chromocenter type as in other genera. At metaphase all the genera investigated of Hamamelidaceae, like other ‘lower’ Hamamelididae, have chromosomes with median centromeres (m-chromosomes), those with submedian centromeres (sm-chromosomes) and those with subterminal (or terminal) centromeres (st-t-chromosomes) at different frequencies, although frequencies ofst-t-chromosomes are always less than 33%. InPlatanus,m-chromosomes are lacking and insteadst-t-chromosomes are predominant (86%), a feature seemingly very specialized. We confirmedx=7 in Platanaceae,x=12 in Hamamelidoideae and Rhodoleioideae, andx=8 in Exbucklandioideae and Altingioideae (Hamamelidaceae). An analysis of chromosome morphology supports the hypothesis thatx=12 in the former two subfamilies is of tetraploid origin fromx=6, rather than of triploid origin fromx=8. We further give brief comments on the suprageneric classification of Hamamelidaceae that was recently proposed by Endress.     

Can obligate apomixis and more stable reproductive assurance explain the distributional successes of asexual triploids in Hieracium alpinum (Asteraceae)?

• Although reproductive assurance has been suggested to be one of the most important factors shaping the differential distributional patterns between sexuals and asexuals (geographic parthenogenesis), it has only rarely been studied in natural populations of vascular plants with autonomous apomixis. Moreover, there are almost no data concerning the putative relationship between the level of apomictic versus sexual plant reproduction on one hand, and reproductive assurance on the other.
• We assessed the level of sexual versus apomictic reproduction in diploid and triploid plants of Hieracium alpinum across its distributional range using flow cytometric analyses of seeds, and compared the level of potential and realized seed set, i.e. reproductive assurance, between the two cytotypes under field and greenhouse conditions.
• Flow cytometric screening of embryos and endosperms of more than 4,100 seeds showed that diploids produced solely diploid progeny sexually, while triploids produced triploid progeny by obligate apomixis. Potential fruit set was much the same in diploids and triploids from the field and the greenhouse experiment. While in the pollination‐limited environment in the greenhouse apomictic triploids had considerably higher realized fruit set than sexual diploids, there was no significant difference between cytotypes under natural conditions. In addition, sexuals varied to a significantly larger extent in realized fruit set than asexuals under both natural and greenhouse conditions.
• Our results indicate that triploid plants reproduce by obligate apomixis, assuring more stable and predictable fruit reproduction when compared to sexual diploids. This advantage could provide apomictic triploids with a superior colonisation ability, mirrored in a strong geographic parthenogenesis pattern observed in this species.

     

DOES HYBRIDIZATION DRIVE THE TRANSITION TO ASEXUALITY IN DIPLOID BOECHERA?

Gametophytic apomixis is a common form of asexual reproduction in plants. Virtually all gametophytic apomicts are polyploids, and some view polyploidy as a prerequisite for the transition to apomixis. However, any causal link between apomixis and polyploidy is complicated by the fact that most apomictic polyploids are allopolyploids, leading some to speculate that hybridization, rather than polyploidy, enables apomixis. Diploid apomixis presents a rare opportunity to isolate the role of hybridization, and a number of diploid apomicts have been documented in the genus Boechera (Brassicaceae). Here, we present the results of a microsatellite study of 1393 morphologically and geographically diverse diploid individuals, evaluating the hypothesis that diploid Boechera apomicts are hybrids. This genus‐wide dataset was made possible by the applicability of a core set of microsatellite loci in 69 of the 70 diploid Boechera species and by our ability to successfully genotype herbarium specimens of widely varying ages. With few exceptions, diploid apomicts exhibited markedly high levels of heterozygosity resulting from the combination of disparate genomes. This strongly suggests that most apomictic diploid Boechera lineages are of hybrid origin, and that the genomic consequences of hybridization allow for the transition to gametophytic apomixis in this genus.     

Karyomorphology ofCrossostylis (Rhizophoraceae)

We present the first report on somatic chromosome numbers and morphology in eight of 13 recorded species ofCrossostylis, one of inland genera of Rhizophoraceae. The chromosome number ofCrossostylis is 2n=28 in all species examined; therefore, the genus hasx=14, a number which is the smallest and unknown elsewhere in the family. Based onCrossostylis raiateensis, we further present that 24 of 28 chromosomes at metaphase have centromeres at median position, and the remaining four at submedian or subterminal position. The chromosome morphology seems to imply thatCrossostylis might be a tetraploid with the original base numberx=7, but an extensive study in the other inland genera is needed to find such a small chromosome number.     

On the origin and evolution of apomixis in Boechera

The genetic mechanisms causing seed development by gametophytic apomixis in plants are predominantly unknown. As apomixis is consistently associated with hybridity and polyploidy, these confounding factors may either (a) be the underlying mechanism for the expression of apomixis, or (b) obscure the genetic factors which cause apomixis. To distinguish between these hypotheses, we analyzed the population genetic patterns of diploid and triploid apomictic lineages and their sexual progenitors in the genus Boechera (Brassicaceae). We find that while triploid apomixis is associated with hybridization, the majority of diploid apomictic lineages are likely the product of intra-specific crosses. We then show that these diploid apomicts are more likely to sire triploid apomictic lineages than conspecific sexuals. Combined with flow cytometric seed screen phenotyping for male and female components of apomixis, our analyses demonstrate that hybridization is an indirect correlate of apomixis in Boechera.     

Genetic relationship among Paspalum species of the subgenus Anachyris: Taxonomic and evolutionary implications

Paspalum is one of the most important genera of the Poaceae family due to its large number of species and diversity. The subgenus Anachyris comprises six species mainly from South America grouped together by sharing rare spikelet characteristics. A genetic analysis using ISSR markers, compared with the morphological and phenotypic variation observed in each one species, was used to establish genetic relationships among 40 accessions with several ploidy levels, belonging to 5 species of the subgenus Anachyris. Fourteen accessions of Paspalum malacophyllum (2x and 4x), 12 of P. simplex (2x, 3x, 4x and 6x), 4 of P. procurrens (2x and 4x), 4 of P. usterii (4x) and 6 of P. volcanensis (4x) were analysed. A total of 227 ISSR loci (98.7% polymorphic) were detected among all accessions, with variable loci number and percentages of polymorphism according to species delimitations. Six main groups were identified by cluster analysis based on Jaccard's genetic distance and UPGMA, four of which matched all the respective accessions of P. simplex, P. procurrens, P. usterii and P. volcanensis, while the other two were consistent with two different groups of accessions of P. malacophyllum, one involving most tetraploid accessions, and the other one grouping together a tetraploid and two diploid accessions. The distinctive morphological characteristics and the separate clustering of these tetraploid and diploid cytotypes suggest to consider a new multiploid species complex inside the subgenus Anachyris. Both cytotypes of P. procurrens, and the four co-specific cytotypes of P. simplex consistently clustered together forming two specific groups for the two multiploid taxons. This is in agreement with the existence of high phenotypic similarities between diploid and tetraploid cytotypes of P. procurrens, and among diploid, triploid, tetraploid and hexaploid cytotypes of P. simplex. Since the polyploid cytotypes of these species are reproduced by apomixis, the specific genetic clustering by ISSR markers and morphological and cytological results support the hypothesis that the two multiploid species were originated by autopolyploidy. Our results confirm previous studies suggesting a monophyletic origin for the subgenus Anachyris and are concordant with previous data regarding genomic homologies and phylogenetic analyses in the genus.     

Cytological and Reproductive Studies on Japanese Diplazium (Woodsiaceae; Pteridophyta): Apomictic Reproduction in Diplazium with Evergreen Bi- to Tripinnate Leaves

Diplazium , including polymorphic terrestrial species with evergreen bi- to tripinnate leaves. Diplazium hachijoense, D. virescens var. virescens, var. conterminum, var. okinawaense, and two other unnamed varieties, D. kawakamii var. kawakamii, D. dilatatum var. heterolepia, D. taiwanense, D. × kawabatae (=D. dilatatum × taiwanense), D. × takii (=D. hachijoense × virescens var. virescens), and D.× nakamurae (= D. hachijoense × virescens var. conterminum) are apomictic triploids (2n=n=123). Diplazium amamianum and D. esculentum are sexual diploids (2n=82, n=41) and D. subtripinnatum is a sexual tetraploid (2n= 164, n=82). Diplazium dilatatum var. dilatatum includes both sexual diploid and apomictic triploid populations. Cultivated gametophytes of six triploid taxa produced sporophytes apogamously, confirming their apomictic reproduction. All three putative hybrids, D. × kawabatae, D. × takii, and D. × nakamurae, are triploid, apomictic, and fertile taxa, therefore they are not the result of hybridization between known pairs of Japanese Diplazium plants. Received 16 March 1999/ Accepted in revised form 30 September 1999     

Physical mapping of ribosomal DNA on several species of the subgenus Rosa

The localization of NORs by fluorescent in situ hybridization on metaphase spreads of five diploid (Rosa gigantea Coll., Rosa moschata Herrm., Rosa multiflora Thunb., Rosa rugosa Thunb. and Rosa sempervirens L., 2n=2x=14), one triploid (Rosa chinensis’semperflorens’ Koehne., 2n=3x=21) and one tetraploid (Rosa gallica ’versicolor’ L., 2n=4x=28) ancestral species of modern roses was studied. Two terminal hybridization signals were observed in all diploid species corresponding to a single NOR per genome in these species. Triploid R. chinensis showed three hybridization sites on the short arm of three morphologically similar chromosomes. Six hybridization sites, located at terminal positions of the short arms of three chromosome pairs, were observed in the tetraploid species. These signals corresponded to three pairs of NORs and all of them were located in chromosome pairs of different size. These observations, together with the analysis of meiotic pairing in PMCs, support the view that our specimen of R. chinensis is an autotriploid and that R. gallica’versicolor’ has an alloploidy nature. Received: 27 November 2000 / Accepted: 12 March 2001     

Chromosome evolution in the Laurales based on analyses of original and published data

We present a summary of currently available chromosome information for all seven families in the order Laurales on the basis of original and previously published data and discuss the evolution of chromosomes in this order. Based on a total of 53 genera for which chromosome data were available, basic chromosome numbers appear consistent within families: x = 11 (Calycanthaceae); x = 22 (Atherospermataceae and Siparunaceae); x = 19 (Monimiaceae); and x = 12 and 15 (Lauraceae). The Hernandiaceae have diverse numbers: x = 15 (Gyrocarpoideae) and x = 18 and 20 (Hernandioideae). Karyotype analyses showed that Hennecartia, Kibaropsis, and Matthaea (all Monimiaceae) contained two or three sets of four distinct chromosomes in 38 somatic chromosomes, suggesting that 2n = 38 was derived by aneuploid reduction from 2n = 40, a tetraploid of x = 10. In light of the overall framework of phylogenetic relationships in the Laurales, we show that x = 11 is an archaic base number in the order and is retained in the Calycanthaceae, which are sister to the remainder of the order. Polyploidization appears to have occurred from x = 11 to x = 22 in a common clade of the Siparunaceae, Atherospermataceae, and Gomortegaceae (although 2n = 42 in the Gomortegaceae), and aneuploid reduction from x = 11 to x = 10 occurred in a common clade of the Hernandiaceae, Lauraceae, and Monimiaceae. To understand chromosome evolution in the Lauraceae, however, more studies are needed of genera and species of Cryptocaryeae.