Molecular confirmation of the genomic constitution of <Emphasis Type="Italic">Douglasdeweya</Emphasis> (Triticeae: Poaceae): demonstration of the utility of the 5S rDNA sequence as a tool for haplome identification

A new genus Douglasdeweya containing the two species, Douglasdeweya deweyi and D. wangii was published in 2005 by Yen et al. based upon the results of cytogenetical and morphological findings. The genome constitution of Douglasdeweya-PPStSt-allowed its segregation from the genus Pseudoroegneria which contains the StSt or StStStSt genomes. Our previous work had demonstrated the utility of using 5S rDNA units, especially the non-transcribed spacer sequence variation, for the resolution of genomes (haplomes) previously established by cytology. Here, we show that sequence analysis of the 5S DNA units from these species strongly supports the proposed species relationships of Yen et al. (Can J Bot 83:413-419, 2005), i.e., the PP genome from Agropyron and the StSt genome from Pseudoroegneria. Analysis of the 5S rDNA units constitutes a powerful tool for genomic research especially in the Triticeae.     

Morphological variation and genome constitution in some perennial Triticeae

JARVIE, J. K. & BARKWORTH, M. E., 1992. Morphological variation and genome constitution in some perennial Triticeae. A numerical analysis of species of five genomically defined genera of the Triticeae was undertaken, based on 42 morphological characters and 142 operational taxonomic units (OTUs). The primary goal was to determine the degree of congruence between morphological variation and genomic constitution. The second goal was to determine which existing supraspecific classification, if any, best reflected the morphological variation encountered. The five genera investigated were Thinopyrum (J genome), Lophopyrum (E genome), Pseudoroegneria (S genome), Trichopyrum (EES genome) and Elytrigia (SJE/SSX genome). Both principal co-ordinate and cluster analysis of the data placed the OTUs in supraspecific groups that reflected their genomic constitution. Monogenomic taxa were clearly separated. Allotetraploids between the E and S genomes were situated between E and S monogenomic taxa. Allotetraploids between the J and E genomes were situated closest to J genome taxa. The EES taxa of Trichopyrum were placed closest to Lophopyrum. OTUs of Elytrigia overlapped those of Pseudoroegneria , but not those of Lophopyrum or Thinopyrum.     

Phylogenetic relationships among diploid Aegilops species inferred from 5S rDNA units

Relationships among the currently recognized 11 diploid species within the genus Aegilops have been investigated. Sequence similarity analysis, based upon 363 sequenced 5S rDNA clones from 44 accessions plus 15 sequences retrieved from GenBank, depicted two unit classes labeled the long AE1 and short AE1. Several different analytical methods were applied to infer relationships within haplomes, between haplomes and among the species, including maximum parsimony and maximum likelihood analyses of consensus sequences, “total evidence” phylogeny analysis and “matrix representation with parsimony” analysis. None were able to depict suites of markers or unit classes that could discern among the seven haplomes as is observed among established haplomes in other genera within the tribe Triticeae; however, most species could be separated when displayed on gene trees. These results suggest that the haplomes currently recognized are so refined that they may be relegated as sub-haplomes or haplome variants. Amblyopyrum shares the same 5S rDNA unit classes with the diploid Aegilops species suggesting that it belongs within the latter. Comparisons of the Aegilops sequences with those of Triticum showed that the long AE1 unit class of Ae. tauschii shared the clade with the equivalent long D1 unit class, i.e., the putative D haplome donor, but the short AE1 unit class did not. The long AE1 unit class but not the short, of Ae. speltoides and Ae. searsii both share the clade with the previously identified long {S1 and long G1 unit classes meaning that both Aegilops species can be equally considered putative B haplome donors to tetraploid Triticum species. The semiconserved nature of the nontranscribed spacer in Aegilops and in Triticeae in general is discussed in view that it may have originated by processes of incomplete gene conversion or biased gene conversion or birth-and-death evolution.     

The 5S rRNA gene in wall barley (Hordeum murinum L. sensu lato): sequence variation among repeat units and relationship to the Y haplome in the genus Hordeum (Poaceae: Triticeae).

The molecular diversity of the 5S rDNA units in 13 accessions of wall barley, which include Hordeum murinum, H. leporinum, and H. glaucum, is reported. Our analyses, based on 54 sequenced clones, indicate the presence of two sequence classes not previously seen in other barley species; namely, the long Y1 unit class and the short Y1 unit class. In addition, the accumulation of new sequence information has allowed us to refine previous groups. Using these new results, along with previously published work, we present a summary of all the unit classes described to date and potential correspondences between 5S rDNA unit classes and haplomes identified previously. In H. murinum, we found the long H1 and long X2 unit classes, and in one of six accessions referable to H. glaucum we found the unique short Y1 unit class. Our cladistic analyses, using orthologous sequences, provide support for the current model for the relationships among several species within the Triticeae.     

A study of 28 Elymus species using repetitive DNA sequences.

Four repetitive DNA sequences cloned from the barley (Hordeum vulgare) genome and common for different Triticeae species were used for a molecular study of phylogenetic relationships among 28 Elymus species. Two wild Hordeum species (H genome), two Pseudoroegneria species (S genome), Agropyron cristatum (P genome), and Australopyrum velutinum (W genome) were included as genomic representatives for the genomes that supposedly were involved in the evolution of the genus Elymus. Our results are essentially congruent with the genomic classification system. This study demonstrates that Elymus is not a monophyletic genus. Based on an analysis of Southern blot hybridization we could discriminate between SY and SH species owing to the strong specific hybridization pattern of the H genome. Hexaploid SYH species gave a hybridization pattern similar to SH species for the same reason. The results support the genomic composition of Elymus batalinii as SYP and also indicated the presence of at least one H genome in Elymus enysii with a hitherto unknown genomic constitution. Elymus erianthus had a hybridization pattern distinctly different from all other species in the investigation. Key words : Elymus, RFLP, phylogeny, repetitive DNA.     

The genome composition of hexaploid Psammopyrum athericum and octoploid Psammopyrum pungens (Poaceae: Triticeae).

The genomic constitution of two species in the genus Psammopyrum, i.e., Ps. athericum (2n = 6x = 42) and Ps. pungens (2n = 8x = 56), was studied by genomic in situ hybridization (GISH). In Ps. athericum, one diploid chromosome set hybridized to a genomic probe from Pseudoroegneria ferganensis (St genome), one diploid set to a probe from Agropyron cristatum (P genome), and one diploid set to a probe from Thinopyrum junceiforme (EbEe genomes) or Th. bessarabicum (Eb genome). Substituting the St-genome probe with an L-genome probe from Festucopsis serpentinii resulted in exactly the same hybridization pattern, suggesting a genomic constitution of EStP or ELP for Ps. athericum. The same probes used on Ps. pungens showed two diploid sets of chromosomes hybridizing to the St-genome probe, one diploid set hybridizing to the P-genome probe, and one diploid set hybridizing to the EbEe-genome probe. The L-genome probe hybridized to approximately 14 of the chromosomes that were labeled by the St-genome probe. Hence the genomic constitution for Ps. pungens is proposed to be EStStP or EStLP.     

Genome Analysis of a Natural Hybrid with 2n= 63 Chromosomes in the Genus Elytrigia Desv. (Poaceae) Using the GISH Technique

Abstract: Genomic in situ hybridization (GISH), using genomic DNA probes from Thinopyrum elongatum (E genome, 2 n = 14), Th. bessarabicum (J genome, 2 n = 14), Pseudoroegneria stipifolia (S genome, 2 n = 14), Agropyron cristatum (P genome, 2 n = 28) and Critesion californicum (H genome, 2 n = 14), was used to identify the genome constitution of a natural hybrid population morphologically close to Elytrigia pycnantha and with somatic chromosome number of 2 n = 63. The GISH results indicated the presence of a chromosomal set more or less closely related to the E, P, S and H genomes. In particular, two sets of 14 chromosomes each showed close affinity to the E genome of Th. elongatum and to the P genome of A. cristatum. However, they included 2 and 10 mosaic chromosomes, respectively, with S genome specific sequences at their centromeric regions. Two additional sets (28 chromosomes) appeared to be very closely related to the S genome of Ps. stipifolia. The last genome involved (7 chromosomes) is related to the H genome of C. californicum but includes one chromosome with S genome-specific sequences around the centromere and two other chromosomes with a short interstitial segment also containing S genome related sequences. On a basis of GISH analysis and literature data, it is hypothesized that the natural 9-ploid hybrid belongs to the genus Elytrigia and results from fertilization of an unreduced gamete (n = 42) of E. pycnantha and a reduced gamete (n = 21) of E. repens. The genomic formula SSSSP^SP^SE^SE^SH^S is proposed to describe its particular genomic and chromosomal composition.     

The 5S DNA sequences in Hordeum bogdanii and in the H. brevisubulatum complex, and the evolution and the geographic dispersal of the diploid Hordeum species (Triticeae: Poaceae).

The molecular diversity of 5S rDNA from the closely related Asiatic diploid species, Hordeum bogdanii and the H. brevisubulatum complex has been catalogued and analysed. As in previous studies in Hordeum, we found that the sequences are constrained in such an manner that unit classes can be defined. The long H1 unit class, known to occur in all Eurasian species, was frequently found in these 2 taxa. In addition, we identified a new unit class, called the short H3 to reflect the H genome found in these 2 taxa. Although the 2 taxa are very close morphologically, the variation in the long H1 DNA units is constrained to such a great degree that, in many cases, the accessions in a unit class from a single species are clustered. In H. bogdanii, the majority of the sequences are grouped in this manner, whereas in the H. brevisubulatum complex, the tendency to be constrained is lower in some but not all subspecies. These results support keeping H. brevisubulatum ssp. violaceum and ssp. iranicum as 1 species with the long H1 and short H1 unit classes, while retaining ssp. nevskianum and ssp. turkestanicum in the H. brevisubulatum complex. We have summarized our work on the presence/absence of the 10 unit classes found in all diploid species of Hordeum. A phylogenetic analysis, based strictly on the presence/absence of unit classes, indicated clearly that all the South American diploids and all the North American diploids possess long H2 and long Y2 unit classes and, except for H. californicum and H. pusillum, which contain long H1 in addition to the long H2 and long Y2 classes, are devoid of the long H1 unit class. This suggests that the gene gain/loss process from a common ancestor has been concomitant with intercontinental dispersal between the Old and the New Worlds.     

Phylogenetic relationships in Elymus (Poaceae: Triticeae) based on the nuclear ribosomal internal transcribed spacer and chloroplast trnL-F sequences

To estimate the phylogenetic relationship of polyploid Elymus in Triticeae, nuclear ribosomal internal transcribed spacer (ITS) and chloroplast trnL-F sequences of 45 Elymus accessions containing various genomes were analysed with those of five Pseudoroegneria (St), two Hordeum (H), three Agropyron (P) and two Australopyrum (W) accessions. The ITS sequences revealed a close phylogenetic relationship between the polyploid Elymus and species from the other genera. The ITS and trnL-F trees indicated considerable differentiation of the StY genome species. The trnL-F sequences revealed an especially close relationship of Pseudoroegneria to all Elymus species included. Both the ITS and trnL-F trees suggested multiple origins and recurrent hybridization of Elymus species. The results suggested that: the St, H, P, and W genomes in polyploid Elymus were donated by Pseudoroegneria, Hordeum, Agropyron and Australopyrum, respectively, and the St and Y genomes may have originated from the same ancestor; Pseudoroegneria was the maternal donor of the polyploid Elymus; and some Elymus species showed multiple origin and experienced recurrent hybridization.     

Molecular diversity of the 5S rRNA gene and genomic relationships in the genus Avena (Poaceae: Aveneae).

The molecular diversity of the rDNA sequences (5S rDNA units) in 71 accessions from 26 taxa of Avena was evaluated. The analyses, based on 553 sequenced clones, indicated that there were 6 unit classes, named according to the haplomes (genomes) they putatively represent, namely the long A1, long B1, long M1, short C1, short D1, and short M1 unit classes. The long and short M1 unit classes were found in the tetraploid A. macrostachya, the only perennial species. The long M1 unit class was closely related to the short C1 unit class, while the short M1 unit class was closely related to the long A1 and long B1 unit classes. However, the short D1 unit class was more divergent from the other unit classes. There was only one unit class per haplome in Avena, whereas haplomes in the Triticeae often have two. Most of the sequences captured belonged to the long A1 unit class. Sequences identified as the long B1 unit class were found in the tetraploids A. abyssinica and A. vaviloviana and the diploids A. atlantica and A. longiglumis. The short C1 unit class was found in the diploid species carrying the C genome, i.e., A. clauda, A. eriantha, and A. ventricosa, and also in the diploid A. longiglumis, the tetraploids A. insularis and A. maroccana, and all the hexaploid species. The short D1 unit class was found in all the hexaploid species and two clones of A. clauda. It is noteworthy that in previous studies the B genome was found only in tetraploid species and the D genome only in hexaploid species. Unexpectedly, we found that various diploid Avena species contained the B1 and D1 units. The long B1 unit class was found in 3 accessions of the diploid A. atlantica (CN25849, CN25864, and CN25887) collected in Morocco and in 2 accessions of A. longiglumis (CIav9087 and CIav9089) collected in Algeria and Libya, respectively, whereas only 1 clone of A. clauda (CN21378) had the short D1 unit. Thus there might be a clue as to where to search for diploids carrying the B and D genomes. Avena longiglumis was found to be the most diverse species, possibly harboring the A, B, and C haplomes. The long M1 and short M1 are the unit classes typical of A. macrostachya. These results could explain the roles of A. clauda, A. longiglumis, and A. atlantica in the evolution of the genus Avena. Furthermore, one clone of the tetraploid A. murphyi was found to have sequences belonging to the short D1 unit class, which could indicate that A. murphyi might have been the progenitor of hexaploid oats and not, as postulated earlier, A. insularis. The evolution of Avena did not follow the molecular clock. The path inferred is that the C genome is more ancient than the A and B genomes and closer to the genome of A. macrostachya, the only existing perennial, which is presumed to be the most ancestral species in the genus.     

Genome analysis of Elytrigia pycnantha and Thinopyrum junceiforme and of their putative natural hybrid using the GISH technique.

Genomic in situ hybridization (GISH), using genomic DNA probes from Thinopyrum elongatum (Host) D.R. Dewey (E genome, 2n = 14), Th. bessarabicum (Savul. & Rayss) A. Love (J genome, 2n = 14), Pseudoroegneria stipifolia (Czern. ex Nevski) Love (S genome, 2n = 14), and Agropyron cristatum (L.) Gaertner (P genome, 2n = 14), was used to characterize the genome constitution of the polyploid species Elytrigia pycnantha (2n = 6x = 42) and Thinopyrum junceiforme (2n = 4x = 28) and of one hybrid population (2n = 5x = 35). GISH results indicated that E. pycnantha contains S, E, and P genomes; the first of these was closely related to the S genome of Ps. stipifolia, the second was closely related to to the E genome of Th. elongatum, and the third was specifically related to A. cristatum. The E and P genomes included 2 and 10 chromosomes, respectively, with S genome DNA sequences in the centromeric region. GISH analysis of Th. junceiforme showed the presence of two sets of the E genome, except for fewer than 10 chromosomes for which the telomeric regions were not identified. Based on these results, the genome formula SSPsPsEsEs is proposed for E. pycnantha and that of EEEE is proposed for Th. junceiforme. The genomic constitution of the pentaploid hybrid comprised one S genome (seven chromosomes), one P genome (seven chromosomes), and three E genomes (21 chromosomes). The E and P genomes both included mosaic chromosomes (chromosomes 1 and 5, respectively) with the centromere region closely related to S-genome DNA. On the basis of these data, the genome formula SPSESEE is suggested for this hybrid and it is also suggested that the two species E. pycnantha and Th. junceiforme are the parents of the pentaploid hybrid.     

The utility of the nontranscribed spacer of 5S rDNA units grouped into unit classes assigned to haplomes - a test on cultivated wheat and wheat progenitors.

Data is presented on the evolutionary dynamics of non-transcribed spacers (NTSs) of 5S rRNA genes in some diploid and polyploid Triticum and Aegilops species. FISH experiments with probes representing different unit classes revealed presence and (or) absence of these sequences in genomes or separate chromosomes of the species. Among the three diploid species only Aegilops speltoides has all of the different unit classes in ribosomal clusters as detected by the probes. Triticum urartu does not have the long D1 signals and Aegilops tauschii does not have the long A1 signals. Both polyploids possess all types of sequences, but because of genome rearrangements after polyploidization there is significant repatterning of single different rDNA unit classes in chromosomal positions when compared with those in diploid progenitors. Additional refined work is needed to ascertain if the sequences in the polyploids are mixed or are located in mini clusters in close proximity to each other. Mantel tests for association between the presence of the FISH signals of the A, B, and D genomes together and separately with the unit class data of the material, i.e., the probes used in FISH, indicated that all signals were associated with their respective probe material, but that there was no association of the unit classes found and the signals to each haplome. All combinations of the partial Mantel tests, e.g., between the A and B haplomes while controlling the effect of the all probes signals, with correlations ranging from 0.48 to 0.79 were all significant. Principal coordinate analysis showed that the signals of most unit class specific probes were more or less equally distant except for the long (S1 and short G1 signals, which were not different, and that the short A1 signals were closely related to the former two, whereas the signals of the long G1 were even less related.     

Evolutionary dynamics of the Pgk1 gene in the polyploid genus Kengyilia (Triticeae: Poaceae) and its diploid relatives

The level and pattern of nucleotide variation in duplicate gene provide important information on the evolutionary history of polyploids and divergent process between homoeologous loci within lineages. Kengyilia is a group of allohexaploid species with the StYP genomic constitutions in the wheat tribe. To investigate the evolutionary dynamics of the Pgk1 gene in Kengyilia and its diploid relatives, three copies of Pgk1 homoeologues were isolated from all sampled hexaploid Kengyilia species and analyzed with the Pgk1 sequences from 47 diploid taxa representing 18 basic genomes in Triticeae. Sequence diversity patterns and genealogical analysis suggested that (1) Kengyilia species from the Central Asia and the Qinghai-Tibetan plateau have independent origins with geographically differentiated P genome donors and diverged levels of nucleotide diversity at Pgk1 locus; (2) a relatively long-time sweep event has allowed the Pgk1 gene within Agropyron to adapt to cold climate triggered by the recent uplifts of the Qinghai-Tibetan Plateau; (3) sweep event and population expansion might result in the difference in the d(N)/d(S) value of the Pgk1 gene in allopatric Agropyron populations, and this difference may be genetically transmitted to Kengyilia lineages via independent polyploidization events; (4) an 83 bp MITE element insertion has shaped the Pgk1 loci in the P genome lineage with different geographical regions; (5) the St and P genomes in Kengyilia were donated by Pseudoroegneria and Agropyron, respectively, and the Y genome is closely related to the Xp genome of Peridictyon sanctum. The interplay of evolutionary forces involving diverged natural selection, population expansion, and transposable events in geographically differentiated P genome donors could attribute to geographical differentiation of Kengyilia species via independent origins.     

Ancient differentiation of the H and I haplomes in diploid Hordeum species based on 5S rDNA.

5S rDNA clones from 12 South American diploid Hordeum species containing the HH genome and 3 Eurasian diploid Hordeum species containing the II genome, including the cultivated barley Hordeum vulgare, were sequenced and their sequence diversity was analyzed. The 374 sequenced clones were assigned to "unit classes", which were further assigned to haplomes. Each haplome contained 2 unit classes. The naming of the unit classes reflected the haplomes, viz. both the long H1 and short I1 unit classes were identified with II genome diploids, and both the long H2 and long Y2 unit classes were recognized in South American HH genome diploids. Based upon an alignment of all sequences or alignments of representative sequences, we tested several evolutionary models, and then subjected the parameters of the models to a series of maximum likelihood (ML) analyses and various tests, including the molecular clock, and to a Bayesian evolutionary inference analysis using Markov chain Monte Carlo (MCMC). The best fitting model of nucleotide substitution was the HKY+G (Hasegawa, Kishino, Yano 1985 model with the Gamma distribution rates of nucleotide substitutions). Results from both ML and MCMC imply that the long H1 and short I unit classes found in the II genome diploids diverged from each other at the same rate as the long H2 and long Y2 unit classes found in the HH genome diploids. The divergence among the unit classes, estimated to be circa 7 million years, suggests that the genus Hordeum may be a paleopolyploid.     

The 5S RNA genes inPinus radiata and the spacer region as a probe for relationships betweenPinus species

The 5S RNA genes inPinus radiata occur in two size classes of about 850 and 525 bp in length. Representatives from both the long and short size classes were cloned and sequenced. The primary difference in the two size classes was shown to be a 330 bp insertion in the spacer region of the long units. Within an individual breeding clone ofP. radiata there was some sequence heterogeneity between representatives of the short class. The 5S RNA genes in thirty pine species were characterised using either a clone of the short size class or a subclone of the 330 bp insertion characterizing the long size class. Eleven species of subg.Strobus were examined and all lacked the long type of unit of radiata pine. The New World species of subg.Pinus all had both short and long units whereas the Old World species had long units. The implications of these results for the evolution of the 5S DNA sequences and the phylogenetic relationships withinPinus are discussed.     

Hystrix patula与Pseudoroegneria libanotica属间杂种的细胞学研究

为研究猬草Hystrixpatula的染色体组组成,进行了H.patula与Pseudoroegnerialibanotica的人工杂交,获得杂种F1,观察了亲本和杂种F1花粉母细胞减数分裂染色体配对行为。杂种F1染色体配对较高,84%的细胞形成7个或7个以上二价体,其构型为6.08Ⅰ+7.48Ⅱ,C-值为0.69。结果表明,H.patula含有St染色体组。     

Hybridisation,genomic constitution and generic delimitation inElymus s. l. (Poaceae: Triticeae)

Intergeneric crosses were made between representatives of the genomically-defined generaElymus, Agropyron, Elytrigia, Pseudoroegneria, andThinopyrum. The genomic constitution ofElytrigia repens, the type species ofElytrigia, is shown to be SSH, a genomic combination otherwise found only inElymus. The S genome ofPseudoroegneria has almost always a dominant influence on the morphology of the taxa of which it is a component.Wang (1989) showed that the J genome inThinopyrum and the S genome have considerable homoeology, with a mean c-value of 0.35 in diploid SJ hybrids. A genetic coherence from S to SJ^e, J^e, J^eJ^b, and J^b can be expected, agreeing with the continuous morphologic variation pattern observed. Because of the absence of morphological discontinuities between the taxa,Pseudoroegneria (S),Elymus (SH, SY, sometimes with additional genomes),Elytrigia (SSH, SSHX), andThinopyrum (SJ, SJJ, J) are best treated as a single genus,Elymus, following the generic concept ofMelderis in Flora Europaea and Flora of Turkey. The basic genomic constituents ofElymus will then be the S and/or J genomes.Agropyron, with diploids, tetraploids, and hexaploids based on the P genome is morphologically distinct from other genera inTriticeae. In a few species ofElymus andPseudoroegneria, a P genome is an additional constituent. In these cases the P genome has a negligible morphological influence. Therefore, it seems reasonable to maintainAgropyron as a separate genus.     

Molecular phylogeny of RNA polymerase II gene reveals the relationships of tetraploid species with St genome (Triticeae: Poaceae)

To evaluate phylogeny of tetraploid with St genome, phylogenetic analyses of RNA polymerase II (RPB2), a member of the nuclear gene family encoding the second largest subunit, were performed. Our results showed that: (1) Roegneria magnicaespes and Roegneria alashanica are related to Pseudoroegneria. (2) Roegneria elytrigioides has StStStSt genomes and should therefore be classified as Pseudoroegneria elytrigioides. (3) Pseudoroegneria tauri and Pseudoroegneria deweyi which have StStPP genomes should be transferred to Douglasdeweya and be renamed as Douglasdeweya wangii and Douglasdeweya deweyi, respectively. (4) Pseudoroegneria geniculata ssp. scythica is related to Pseudoroegneria and Lophyrum, and hence should be identified as a species of Trichopyrum. (5) Pseudoroegneria libanotica might be a parental donor for Elytrigia caespitosa rather than Elytrigia caespitosa ssp. nodosa. It is unreasonable to recognize El. caespitosa ssp. nodosa as a subspecies of El. caespitosa. (6) Interspecific and intergeneric variations are detected in St genome of these tetraploid species.     

Phylogenetic analysis of North American Elymus and the monogenomic Triticeae (Poaceae) using three chloroplast DNA data sets.

Although the monogenomic genera of the Triticeae have been analyzed in numerous biosystematic studies, the allopolyploid genera have not been as extensively studied within a phylogenetic framework. We focus on North American species of Elymus, which, under the current genomic system of classification, are almost all allotetraploid, combining the St genome of Pseudoroegneria with the H genome of Hordeum. We analyze new and previously published chloroplast DNA data from Elymus and from most of the monogenomic genera of the Triticeae in an attempt to identify the maternal genome donor of Elymus. We also present a cpDNA phylogeny for the monogenomic genera that includes more data than, and thus builds on, those previously published. The chloroplast DNA data indicate that Pseudoroegneria is the maternal genome donor to all but one of the Elymus individuals. There is little divergence among the Elymus and Pseudoroegneria chloroplast genomes, and as a group, they show little divergence from the rest of the Triticeae. Within the monogenomic Triticeae, the problematic group Thinopyrum is resolved as monophyletic on the chloroplast DNA tree. At the intergeneric level, the data reveal several deeper-level relationships that were not resolved by previous cpDNA trees.