Parallel polyploid speciation: distinct sympatric gene‐pools of recurrently derived allo‐octoploid Asplenium ferns

Although polyploidy is widespread, its significance to the generation of biodiversity remains unclear. Many polyploids have been derived recurrently. For a particular polyploid, gene‐flow between the products of independent origin is typical where they come into contact. Here, we use AFLP DNA‐fingerprinting and chloroplast DNA sequences to demonstrate parallel polyploid speciation within both of the ferns Asplenium cimmeriorum and A. gracillimum. Both of these taxa comprise at least two allopolyploids, recurrently derived from the same progenitor pair. Each of these allopolyploids remain genetically distinguishable even with extensive sympatry, and could therefore be considered distinct species. To our knowledge, parallel speciation on this scale amongst recurrent polyploids has not been previously reported. With their parallel origins, these ‘evolutionary replicates’ provide an unrivalled opportunity to investigate how the reproductive barriers and ecological differentiation necessary for speciation arise following polyploidy.     

荧光原位杂交技术在植物多倍体起源与进化研究中的应用

多倍化是植物物种形成与多样化的重要原动力。研究植物特别是一些重要经济作物和园艺植物多倍体的起源与进化,不仅对于揭示多倍体形成过程中性状变异的分子机制具有重要意义,而且可为植物遗传资源的保护与利用提供理论和技术支持。作为连接基因组序列片段到染色体组的桥梁,荧光原位杂交技术长期被广泛用来研究多倍体形成与进化过程中相关特异基因或序列的表达定位、外源染色体检测和鉴定、基因组结构变异等科学问题。因此,在简单介绍荧光原位杂交技术发展历史和植物多倍体主要类型的基础上,主要总结了荧光原位杂交技术在植物多倍体起源与进化相关研究上的应用。     

Inferring the mode of origin of polyploid species from next‐generation sequence data

Many eukaryote organisms are polyploid. However, despite their importance, evolutionary inference of polyploid origins and modes of inheritance has been limited by a need for analyses of allele segregation at multiple loci using crosses. The increasing availability of sequence data for nonmodel species now allows the application of established approaches for the analysis of genomic data in polyploids. Here, we ask whether approximate Bayesian computation (ABC), applied to realistic traditional and next‐generation sequence data, allows correct inference of the evolutionary and demographic history of polyploids. Using simulations, we evaluate the robustness of evolutionary inference by ABC for tetraploid species as a function of the number of individuals and loci sampled, and the presence or absence of an outgroup. We find that ABC adequately retrieves the recent evolutionary history of polyploid species on the basis of both old and new sequencing technologies. The application of ABC to sequence data from diploid and polyploid species of the plant genus Capsella confirms its utility. Our analysis strongly supports an allopolyploid origin of C. bursa‐pastoris about 80 000 years ago. This conclusion runs contrary to previous findings based on the same data set but using an alternative approach and is in agreement with recent findings based on whole‐genome sequencing. Our results indicate that ABC is a promising and powerful method for revealing the evolution of polyploid species, without the need to attribute alleles to a homeologous chromosome pair. The approach can readily be extended to more complex scenarios involving higher ploidy levels.     

A novel method to infer the origin of polyploids from Amplified Fragment Length Polymorphism data reveals that the alpine polyploid complex of Senecio carniolicus (Asteraceae) evolved mainly via autopolyploidy

Despite its evolutionary and ecological relevance, the mode of polyploid origin has been notoriously difficult to be reconstructed from molecular data. Here, we present a method to identify the putative parents of polyploids and thus to infer the mode of their origin (auto‐ vs. allopolyploidy) from Amplified Fragment Length Polymorphism (AFLP) data. To this end, we use Cohen's d of distances between in silico polyploids, generated within a priori defined scenarios of origin from a priori delimited putative parental entities (e.g. taxa, genetic lineages), and natural polyploids. Simulations show that the discriminatory power of the proposed method increases mainly with increasing divergence between the lower‐ploid putative ancestors and less so with increasing delay of polyploidization relative to the time of divergence. We apply the new method to the Senecio carniolicus aggregate, distributed in the European Alps and comprising two diploid, one tetraploid and one hexaploid species. In the eastern part of its distribution, the S. carniolicus aggregate was inferred to comprise an autopolyploid series, whereas for western populations of the tetraploid species, an allopolyploid origin involving the two diploid species was the most likely scenario. Although this suggests that the tetraploid species has two independent origins, other evidence (ribotype distribution, morphology) is consistent with the hypothesis of an autopolyploid origin with subsequent introgression by the second diploid species. Altogether, identifying the best among alternative scenarios using Cohen's d can be straightforward, but particular scenarios, such as allopolyploid origin vs. autopolyploid origin with subsequent introgression, remain difficult to be distinguished.     

Propagule pressure and the establishment of emergent polyploid populations

BackgroundWhereas the incidence or rate of polyploid speciation in flowering plants is modest, the production of polyploid individuals within local populations is widespread. Explanations for this disparity primarily have focused on properties or interactions of polyploids that limit their persistence.HypothesisThe emergence of local polyploid populations within diploid populations is similar to the arrival of invasive species at new, suitable sites, with the exception that polyploids suffer interference from their progenitor(s). The most consistent predictor of successful colonization by invasive plants is propagule pressure, i.e. the number of seeds introduced. Therefore, insufficient propagule pressure, i.e. the formation of polyploid seeds within diploid populations, ostensibly is a prime factor limiting the establishment of newly emergent polyploids within local populations. Increasing propagule number reduces the effects of genetic, environmental and demographic stochasticity, which thwart population survival. As with invasive species, insufficient seed production within polyploid populations limits seed export, and thus reduces the chance of polyploid expansion.ConclusionThe extent to which propagule pressure limits the establishment of local polyploid populations remains to be determined, because we know so little. The numbers of auto- or allopolyploid seed in diploid populations rarely have been ascertained, as have the numbers of newly emergent polyploid plants within diploid populations. Moreover, seed production by these polyploids has yet to be assessed.     

Distribution of basic diploid and polyploid species of Isoetes in East Asia

Aims Isoetes L. is an ancient, primitive genus of heterosporous lycopsids characterized by a strongly reduced plant. The genus occupies a unique position in plant evolution as the closest relatives of the famous tree lycopods. Hybridization and allopolyploid speciation as well as habitat preference are regarded as having played an important role in the evolution of the genus Isoetes. However, it is still uncertain what factors have impacted upon hybridization and allopolyploid speciation of the genus Isoetes. Our understanding of the origin, evolution and modern distribution pattern of Isoetes in East Asia would benefit from investigations into the relationship between the unique geographical location and topographic features and the existing fossil record in the region. Methods The chromosome number was determined from known 81 populations of 10 species of Isoetes in East Asia. The altitude was obtained in location of every population. T‐test was used to evaluate the altitude difference between diploid and polyploid populations. Data of Japanese Isoetes from Takamiya et al. was used in the study. Results There are 10 known species of Isoetes with four diploids and six polyploids in East Asia. The four diploid species (2n = 22) are found at high altitudes (mean altitude = 2649.67 ± 1396.16 m, n = 18) and isolated from each other. In contrast, the six polyploid species widely occur in low altitude regions (mean altitude = 182.62 ± 181.44 m, n = 63) and are partially sympatric. Highly significant differences (P < 0.001) were observed between the mean altitude of locations of populations of diploids and polyploids. Main conclusions The polyploidy speciations of Isoetes in East Asia might originate and develop from Holocene (Quaternary). The present pattern of distribution of Isoetes in East Asia is the result of allopatric speciation derived from vicariance, dispersal and combinations of both, and significantly correlative with the geological history and geographical changes. The change of altitude might have played an important role in allopolyploid speciation and the pattern of distribution of the genus Isoetes in East Asia by exerting a considerable influence on dispersal and hybridization opportunities of Isoetes species.     

Allopolyploidy in the Thalloid Liverwort Corsinia (Marchantiales)

The thalloid liverwort Corsinia coriandrina includes morphologically similar haploid and polyploid populations with an allopatric geographical distribution. Haploid and polyploid colonies of the Old World, and one polyploid colony from Texas have been analysed. The polyploid, monoecious cytotype has a wider geographical range and ecological tolerance than the haploid, dioecious cytotype which appears to be restricted to southern Europe and Macaronesia. Similarity coefficients between the two Old World cytotypes based on isozyme data show them to be more genetically divergent than suggested by their morphology, and to fit the definition of sibling species. Fixed heterozygosity in six of eight enzyme loci suggests an alloploid origin of the Old World polyploids. The haploid cytotype could be one of the putative parents. Alleles in the polyploid that were not detected in the haploid are presumably derived from an unknown progenitor. The polyploid New World colony shows significant genetic divergence; it represents a different allopolyploid sibling species. Accordingly, at least two independent origins of the polyploid must be supposed; one in the Old World; the other in the New World. The presumed autopolyploid origin of polyploid liverworts is once more challenged by our analysis of polyploid Corsinia. Indeed, autopolyploidy has still not been documented conclusively in any polyploid liverwort.     

Polyploidy, hybridization and reticulate evolution: lessons from the Brassicaceae

The family Brassicaceae is well known for its large variation in chromosome numbers, common occurrence of polyploids and many reports of interspecific gene flow. The present review summarizes studies from the past decades on polyploidization and hybridization events, recognizing them as important evolutionary forces in the family. Attention is drawn to the issue of the reconstruction of reticulated pattern of evolution resulting from allopolyploid and homoploid hybrid speciation. The research of various authors on several Brassicaceae genera is presented and discussed in the context of our current understanding of polyploid and hybrid evolution. Model species, Arabidopsis thaliana and Brassica taxa, are referred to only marginally, major focus is on a comprehensive survey of studies on about a dozen best explored non-model genera (e.g. Cardamine, Draba, Rorippa, Thlaspi). The increasing amount of genetic and genomic resources available for Brassicaceae model species provides excellent opportunities for comparative genetic and genomic studies. Future research directions and challenges are thus outlined, in order to obtain more detailed insights into the evolution of polyploid and hybrid genomes.     

Polyploid plants have faster rates of multivariate niche differentiation than their diploid relatives

Polyploid speciation entails substantial and rapid postzygotic reproductive isolation of nascent species that are initially sympatric with one or both parents. Despite strong postzygotic isolation, ecological niche differentiation has long been thought to be important for polyploid success. Using biogeographic data from across vascular plants, we tested whether the climatic niches of polyploid species are more differentiated than their diploid relatives and if the climatic niches of polyploid species differentiated faster than those of related diploids. We found that polyploids are often more climatically differentiated from their diploid parents than the diploids are from each other. Consistent with this pattern, we estimated that polyploid species generally have higher rates of multivariate niche differentiation than their diploid relatives. In contrast to recent analyses, our results confirm that ecological niche differentiation is an important component of polyploid speciation and that niche differentiation is often significantly faster in polyploids.     

Oilseed rape: learning about ancient and recent polyploid evolution from a recent crop species

Oilseed rape (Brassica napus) is one of our youngest crop species, arising several times under cultivation in the last few thousand years and completely unknown in the wild. Oilseed rape originated from hybridisation events between progenitor diploid species B. rapa and B. oleracea, both important vegetable species. The diploid progenitors are also ancient polyploids, with remnants of two previous polyploidisation events evident in the triplicated genome structure. This history of polyploid evolution and human agricultural selection makes B. napus an excellent model with which to investigate processes of genomic evolution and selection in polyploid crops. The ease of de novo interspecific hybridisation, responsiveness to tissue culture, and the close relationship of oilseed rape to the model plant Arabidopsis thaliana, coupled with the recent availability of reference genome sequences and suites of molecular cytogenetic and high‐throughput genotyping tools, allow detailed dissection of genetic, genomic and phenotypic interactions in this crop. In this review we discuss the past and present uses of B. napus as a model for polyploid speciation and evolution in crop species, along with current and developing analysis tools and resources. We further outline unanswered questions that may now be tractable to investigation.     

Physical mapping of rDNA sites in possible diploid progenitors of polyploid Festuca species

Festuca species form a polyploid series but only two of the diploid species have been firmly proposed as progenitors of any polyploid. The number and distribution of rDNA sites on the chromosomes of F. scariosa (section Scariosae) and the four diploid species that comprise section Montanae are presented with their relative DNA amounts and key morphological features. Comparisons of the results with those of some polyploid Festuca species from section Bovinae published previously indicate that F. scariosa and F. altissima could be diploid progenitors of the polyploids. It is unlikely that any one of the other three Montanae species is a progenitor of these polyploids.     

CHROMOSOMES AND CROSSING BEHAVIOR OF SOME SPECIES OF SANSEVIERIA

Menzel , Margaret Y. (Florida State U., Tallahassee), and James B. Pate . Chromosomes and crossing behavior of some species of Sansevieria. Amer. Jour. Bot. 47(3) : 230—238. Illus. 1960.–Approximately 20 species (28 clones) studied were diploids, tetraploids or hexaploids of the basic numbers x = 20; about 40% of the taxa were polyploid. All species had similar karyotypes, except for chromosome number. Five of 12 combinations of diploid species gave fertile F₁ hybrids; 4 studied cytologically showed 20 bivalents at metaphase I. Two triploid interspecific hybrids showed high trivalent frequencies. In contrast, multivalent formation in polyploid species was variable but rather low. Morphological relationships appeared reticulate among and between diploids and polyploids and did not coincide with barriers to crossing or to hybrid fertility. The following tentative hypothesis concerning relationships in the genus is proposed: Sansevieria is monophyletic and speciation has proceeded through genetic variation and hybridization at the diploid level and by allopolyploidy (of the segmental type) ; a low level of chromosome differentiation has accompanied speciation such that complete pairing occurs in diploid hybrids, but considerable preferential pairing occurs in allopolyploids. The occurrence of both polyploid and hybrid vigor, the fertility of hybrids between species differing greatly in morphology and physiology, and the high potential for vegetative propagation make the genus a favorable subject for breeding based on interspecific hybridization.     

Time-calibrated phylogenetic trees establish a lag between polyploidisation and diversification in <Emphasis Type="Italic">Nicotiana</Emphasis> (Solanaceae)

We investigate the timing of diversification in allopolyploids of Nicotiana (Solanaceae) utilising sequence data of maternal and paternal origin to look for evidence of a lag phase during which diploidisation took place. Bayesian relaxed clock phylogenetic methods show recent allopolyploids are a result of several unique polyploidisation events, and older allopolyploid sections have undergone subsequent speciation at the polyploid level (i.e. a number of these polyploid species share a singular origin). The independently formed recent polyploid species in the genus all have mean age estimates below 1 million years ago (Ma). Nicotiana section Polydicliae (two species) evolved 1.5 Ma, N. section Repandae (four species) formed 4 Ma, and N. section Suaveolentes (~35 species) is about 6 million years old. A general trend of higher speciation rates in older polyploids is evident, but diversification dramatically increases at approximately 6 Ma (in section Suaveolentes). Nicotiana sect. Suaveolentes has spectacularly radiated to form 35 species in Australia and some Pacific islands following a lag phase of almost 6 million years. Species have filled new ecological niches and undergone extensive diploidisation (e.g. chromosome fusions bringing the ancestral allotetraploid number, n = 24, down to n = 15 and ribosomal loci numbers back to diploid condition). Considering the progenitors of Suaveolentes inhabit South America, this represents the colonisation of Australia by polyploids that have subsequently undergone a recent radiation into new environments. To our knowledge, this study is the first report of a substantial lag phase being investigated below the family level.     

Cytogeography and chromosomal variation of the endemic East Asian herb Lycoris radiata

Information on the spatial distribution of cytotypes and karyotype variation in plants is critical for studies of the origin and evolution of polyploid complexes. Here, the spatial distribution of cytological races and intraspecific variation in the karyotype of Lycoris radiata, an endemic species to East Asia, is investigated. Conventional karyotype analysis methods were used to determine ploidy level and karyotypical characteristics in 2,420 individuals from 114 populations of L. radiata nearly covering the whole distribution areas in China. Of 114 populations studied, 52 (45.61%), 58 (50.88%), and 4 (3.51%) are diploid, triploid, and mixoploid populations, respectively, with 1,224, 1,195, and 1 individuals being diploid, triploid, and tetraploid, respectively. The triploid possesses a much wider distribution range than the diploid, with the former almost occupying the entire range of this complex species in East Asia and the latter distributing in the middle and east regions of China. Triploids tend to occur at high altitudes, and the relationship between the ploidy and altitude is significantly positive but low (r² = 0.103, p < 0.01). About 98.6% of examined bulbs have a common karyotype consisting of 22 or 33 acrocentric (A) chromosomes. Some aberrant chromosomes which should be generated from A‐type chromosome have been found including metacentrics (m), small metacentrics (m′), and B‐type chromosome. The results can provide a fundamental cytogeographic data for further studies on the evolutionary origins and adaptive divergences of polyploids, especially the triploid, within L. radiata using molecular and/or ecological methods in the future.     

RECURRENT FORMATION AND POLYPHYLY OF NORDIC POLYPLOIDS IN DRABA (BRASSICACEAE)

Draba (Brassicaceae) is well known for its taxonomic complexity in arctic and alpine floras, and the polyploids in particular present vexing taxonomic problems. It has been suggested that polyploids in Draba may have formed recurrently from different populations of the parental species (polytopy), and it is also possible that a given taxonomic species may actually comprise several polyploid races, each originating from different progenitor species (polyphyly). To unravel the taxonomic complexity of polyploid Draba in the Nordic area, we investigated three of the most morphologically variable species and their possible progenitors using enzyme electrophoresis and restriction site analysis of chloroplast DNA (cpDNA) and nuclear ribosomal RNA genes (rDNA): D. norvegica (6x), D. lactea (6x), and D. corymbosa (16x). Electrophoretic analyses of progeny showed high levels of fixed heterozygosity in all three polyploids, demonstrating that all are genetic alloploids. Electrophoretic and rDNA data indicate that polytopic and/or polyphyletic origins have contributed to the complexity of these polyploids. However, a lack of cpDNA variation among the species limited the usefulness of this molecule for analysis of polyploid origins. The considerable electrophoretic variation observed in D. norvegica necessitates a minimum of three and probably 13 independent origins. Electrophoretic and rDNA data suggest that D. lactea and D. corymbosa are polyphyletic polyploids. Crossing data also support that D. corymbosa is polyphyletic. Given the widespread geographic distributions of these species and their possible progenitors, and that the populations analyzed represent only a small fraction of their geographic distributions, it is likely that these species have formed numerous times in different areas. As more molecular analyses of polyploids are completed, the data continue to suggest that multiple origins of polyploids are the rule rather than the exception.     

Genetic diversity patterns in Curcuma reflect differences in genome size

The relationships between genome size and the systematic and evolutionary patterns in vascular plants are equivocal, although a close relationship between genome size and evolutionary patterns has been previously reported. However, several studies have also revealed the dynamic nature of genome size evolution and its considerable ‘ups’ and ‘downs’. Thus, in this study, the phylogenetic relationships among three previously revealed genome size groups and among species of the highly polyploid genus Curcuma were evaluated using AFLP. Our results suggest two main lineages within Indian Curcuma reflecting evolution of genome size. The first one includes hexaploids and higher polyploids of the previously recognized genome size group I, and the second one includes mainly hexaploids of genome size groups II and III. Within genome size group I, relationships among species seem to be influenced by reticulate evolution and higher polyploids are likely to be of allopolyploid origin. Reproductive systems in Indian Curcuma vary considerably among ploidy levels and these differences considerably affect morphological and genetic variation. In general, clonally reproducing species are expected to exhibit low genotypic diversity, but, at the same time, species of allopolyploid origin are expected to maintain higher levels of heterozygosity compared with their progenitors. We investigated intra‐populational genetic variability in Curcuma spp. to evaluate whether mode of reproduction or ploidy represent the main factor influencing the degree of genetic diversity. We found that hexaploid species exhibited significantly higher genetic diversity than higher polyploids (9x, 15x). Our results suggest that this genetic diversity pattern is largely influenced by the mode of reproduction, as higher polyploids reproduce exclusively vegetatively, whereas hexaploids reproduce mainly sexually. © 2011 The Linnean Society of London, Botanical Journal of the Linnean Society, 2011, 165 , 388–401.     

Untangling Nucleotide Diversity and Evolution of the H Genome in Polyploid Hordeum and Elymus Species Based on the Single Copy of Nuclear Gene DMC1

Numerous hybrid and polypoid species are found within the Triticeae. It has been suggested that the H subgenome of allopolyploid Elymus (wheatgrass) species originated from diploid Hordeum (barley) species, but the role of hybridization between polyploid Elymus and Hordeum has not been studied. It is not clear whether gene flow across polyploid Hordeum and Elymus species has occurred following polyploid speciation. Answering these questions will provide new insights into the formation of these polyploid species, and the potential role of gene flow among polyploid species during polyploid evolution. In order to address these questions, disrupted meiotic cDNA1 (DMC1) data from the allopolyploid StH Elymus are analyzed together with diploid and polyploid Hordeum species. Phylogenetic analysis revealed that the H copies of DMC1 sequence in some Elymus are very close to the H copies of DMC1 sequence in some polyploid Hordeum species, indicating either that the H genome in theses Elymus and polyploid Hordeum species originated from same diploid donor or that gene flow has occurred among them. Our analysis also suggested that the H genomes in Elymus species originated from limited gene pool, while H genomes in Hordeum polyploids have originated from broad gene pools. Nucleotide diversity (π) of the DMC1 sequences on H genome from polyploid species (π = 0.02083 in Elymus, π = 0.01680 in polyploid Hordeum) is higher than that in diploid Hordeum (π = 0.01488). The estimates of Tajima''s D were significantly departure from the equilibrium neutral model at this locus in diploid Hordeum species (P<0.05), suggesting an excess of rare variants in diploid species which may not contribute to the origination of polyploids. Nucleotide diversity (π) of the DMC1 sequences in Elymus polyploid species (π = 0.02083) is higher than that in polyploid Hordeum (π = 0.01680), suggesting that the degree of relationships between two parents of a polyploid might be a factor affecting nucleotide diversity in allopolyploids.     

DYNAMICS OF POLYPLOID FORMATION IN TRAGOPOGON (ASTERACEAE): RECURRENT FORMATION,GENE FLOW,AND POPULATION STRUCTURE

Polyploidy is a major feature of angiosperm evolution and diversification. Most polyploid species have formed multiple times, yet we know little about the genetic consequences of recurrent formations. Among the clearest examples of recurrent polyploidy are Tragopogon mirus and T. miscellus (Asteraceae), each of which has formed repeatedly in the last ～80 years from known diploid progenitors in western North America. Here, we apply progenitor‐specific microsatellite markers to examine the genetic contributions to each tetraploid species and to assess gene flow among populations of independent formation. These data provide fine‐scale resolution of independent origins for both polyploid species. Importantly, multiple origins have resulted in considerable genetic variation within both polyploid species; however, the patterns of variation detected in the polyploids contrast with those observed in extant populations of the diploid progenitors. The genotypes detected in the two polyploid species appear to represent a snapshot of historical population structure in the diploid progenitors, rather than modern diploid genotypes. Our data also indicate a lack of gene flow among polyploid plants of independent origin, even when they co‐occur, suggesting potential reproductive barriers among separate lineages in both polyploid species.     

CHROMOSOME NUMBERS IN CUPHEA (LYTHRACEAE): NEW COUNTS AND A SUMMARY

The American genus Cuphea with ca. 260 species is extremely diverse with respect to chromosome number. Counts are now available for 78 species and/or varieties, or 29% of the genus. Included in this study are first reports for 15 taxa from Brazil, Cuba, Dominican Republic, Mexico, and Venezuela. Twenty-two different numbers are known for the genus, ranging from n = 6 to n = 54. The most common number in the primary center of species diversity in Brazil is n = 8, which is regarded as the base number of the genus. Two numbers are most common in the secondary center in Mexico, n = 10 and n = 12. Species with n = 14 or higher are considered to be of polyploid origin. Polyploids comprise 46% of the total species counted and appear in 9 of the 11 sections for which chromosome numbers have been reported. Aneuploid species comprise ca. 25% of the genus and are known from 7 of the 11 sections. The two subgenera are not characterized by different chromosome numbers or sequences of numbers. None of the 14 sections are circumscribed by a single chromosome number. Morphological and ecological variability in widespread, weedy species is correlated with differing chromosome numbers in some species whereas in others the chromosome number is stable. Summary of chromosome numbers by taxonomic section is presented. Section Euandra, centered in eastern Brazil, and the largest section of the genus, appears to be chromosomally most diverse. In section Trispermum, characterized by difficult, variable species with intermediate forms, two of the four species studied have polyploid races. Section Heterodon, endemic to Mexico and Central America and comprising most of the annual species of the genus, is best known chromosomally. Chromosome numbers have been counted for 25 of 28 species, and 12 different numbers are reported. The most advanced sections, Melvilla and Diploptychia, with numerous species occurring at higher altitudes, are characterized by high polyploids. Apomictic species occur in sect. Diploptycia. The cytoevolution of Cuphea is complex with frequent polyploid and aneuploid events apparently playing a significant role in speciation in both centers of diversity.     

Assessing the monophyly of polyploid Gossypium species

The origin and monophyly of the polyploid cotton (Gossypium) species has been largely accepted, despite the lack of explicit phylogenetic evidence. Recent studies in other polyploid systems have demonstrated that multiple origins for polyploid species are much more common than once thought, raising the possibility that Gossypium polyploids also had multiple origins, as postulated by some authors. To test the monophyly of polyploid cotton, we sequenced a 2.8-kb intergenic region from all diploid species belonging to the genome groups from which the polyploid originates. The resulting phylogenetic analyses strongly support a single origin of polyploid cotton involving a D-genome ancestor related to Gossypium raimondii and an A-genome ancestor that was sister to both extant A-genome species.