Nuclear Ribosomal Repeat Research Articles

Phylogeny of lichen- and non-lichen-forming omphalinoid mushrooms and the utility of testing for combinability among multiple data sets.

As an initial step toward developing a model system to study requirements for and consequences of transitions to mutualism, the phylogeny of a group of closely related lichenized and nonlichenized basidiomycetes (Omphalina) was reconstructed. The phylogenetic analyses are based on four data sets representing different regions of the nuclear ribosomal repeat unit (ITS1, 5.8S, ITS2, and 25S) obtained from 30 species of Omphalina and related genera. The resulting phylogenetic trees from each of these four data sets, when analyzed separately, were not identical. Testing for the combinability of these four data sets suggested that they could not be combined in their entirety. The removal of ambiguous alignments and saturated sites was sufficient, after reapplying the combinability test on the pruned data sets, to explain the topological discrepancies. In this process, the first of two complementary tests developed by Rodrigo et al. (1993, N.Z. J. Bot. 31:257-268) to assess whether two data sets are the result of the same phylogenetic history was found to be biased, rejecting the combinability of two data sets even when they are samples of the same phylogenetic history. Combining the four pruned data sets yielded phylogenies that suggest the five lichen-forming species of Omphalina form a monophyletic group. The sister group to this symbiotic clade consists mostly of dark brown Omphalina species intermixed with species from the genera Arrhenia and Phaeothellus. The genera Omphalina and Gerronema are shown to be polyphyletic. The lichen-forming species O. ericetorum and the nonmutualistic species O. velutipes, O. epichysium, and O. sphagnicola are the best candidates for experimental work designed to gain a better understanding of mechanisms involved in symbiotic interactions and the role symbiosis has played in the evolution of fungi.

THE EVOLUTION OF PARASITES FROM THEIR HOSTS: A CASE STUDY IN THE PARASITIC RED ALGAE.

Morphological similarities of many parasites and their hosts have led to speculation that some groups of plant, animal, fungal, and algal parasites may have evolved directly from their hosts. These parasites, which have been termed adelphoparasites in the botanical literature, and more recently, agastoparasites in the insect literature, may evolve monophyletically from one host and radiate secondarily to other hosts or, these parasites may arise polyphyletically, each arising from its own host. In this study we compare the internal transcribed spacer regions of the nuclear ribosomal repeats of species and formae specialis (host races) included in the red algal parasite genus Asterocolax with its hosts, which all belong to the Phycodrys group of the Delesseriaceae and with closely related nonhost taxa of the Delesseriaceae. These analyses reveal that species of Asterocolax have evolved polyphyletically. Asterocolax erythroglossi from the North Atlantic host Erythroglossum laciniatum appears to have evolved from its host, whereas taxa included in the north Pacific species Asterocolax gardneri have had two independent origins. Asterocolax gardneri from the host Polyneura latissima probably arose directly from this host. In contrast, all other A. gardneri formae specialis appear to have originated from either Phycodrys setchellii or P. isabelliae and radiated secondarily onto other closely related taxa of the Phycodrys group, including Nienburgia andersoniana and Anisocladella pacifica. Gamete crossing experiments confirm that A. gardneri from each host is genetically isolated from both its host, and from other A. gardneri and their hosts. Cross-infection experiments reveal that A. gardneri develops normally only on its natural host, although some abberrant growth may occur on alternate hosts. The ability of red algal parasites to radiate secondarily to other red algal taxa, where they may become isolated genetically and speciate, suggests that this process of speciation is not a "genetic dead end" but one that may give rise to related clusters of parasite species.

Molecular revisitation of the genus Gastrosuillus

We have used internal transcribed spacer sequences from the nuclear ribosomal repeat to investigate the secotioid genus Gastrosuillus and to clarify its relationship to Suillus. Our results show that secotioid fruitbodies in the genus Gastrosuillus are clearly derived and have evolved at least two times from Suillus. Gastrosuillus suilloides, Gastrosuillus amaranthii, and Gastrosuillus umbrinus proved to be genetically very closely related; their closest nonsecotioid relative was found to be Suillus variegatus. Gastrosuillus laricinus has been shown before to be a recent derivative of Suillus grevillei. Due to its polyphyletic and derived nature, we propose to collapse the genus Gastrosuillus into Suillus.

Molecular Revisitation of the Genus Gastrosuillus

We have used internal transcribed spacer sequences from the nuclear ribosomal repeat to investigate the secotioid genus Gastrosuillus and to clarify its relationship to Suillus. Our results show that secotioid fruitbodies in the genus Gastrosuillus are clearly derived and have evolved at least two times from Suillus. Gastrosuillus suilloides, Gastrosuillus amaranthii, and Gastrosuillus umbrinus proved to be genetically very closely related; their closest nonsecotioid relative was found to be Suillus variegatus. Gastrosuillus laricinus has been shown before to be a recent derivative of Suillus grevillei. Due to its polyphyletic and derived nature, we propose to collapse the genus Gastrosuillus into Suillus.

Polymorphisms in the Large Intergenic Spacer of the Nuclear Ribosomal Repeat Identify Laccaria proxima Strains

A simple method for identifying strains of Lacearia proxima is presented which uses the polymerase chain reaction (PCR) to amplify the large intergenic spacer region of the nuclear ribosomal repeat. The large intergenic spacer region of L. proxima is approximately 4000 base pairs long and is variable enough to permit clear identification of individual strains after digestion with restriction endonucleases. This has only been partially possible with other published PCR-based identification methods which use conserved primers. The method has the potential to be adapted for use in identifying isolates directly from roots and avoids the use of labeled probes needed for identifying Laccaria strains with techniques which are not PCR-based.

Internal transcribed spacer sequences from 38 recognized species ofSuillussensu lato: Phylogenetic and taxonomic implications

Internal transcribed spacer regions of the nuclear ribosomal repeat have been sequenced from 47 isolates belonging to 38 recognized species of Suil- lus sensu lato. The sequences have been analyzed for phylogenetic and taxonomic implications using par- simony as well as distance methods. Based on these data, the genera Boletinus and Fuscoboletinus, that are often recognized within Suillus sensu lato, are not monophyletic. Isolates of Suillus granulatus derived from either North America or Europe and Asia are polyphyletic and seem to represent at least two dif- ferent species. Our data also suggest that within Suil- lus sensu lato, mycorrhizal associations with Larix are primitive and host changes to Pinus and Pseudotsuga

Internal Transcribed Spacer Sequences from 38 Recognized Species of Suillus sensu lato: Phylogenetic and Taxonomic Implications

Internal transcribed spacer regions of the nuclear ribosomal repeat have been sequenced from 47 isolates belonging to 38 recognized species of Suillus sensu lato. The sequences have been analyzed for phylogenetic and taxonomic implications using parsimony as well as distance methods. Based on these data, the genera Boletinus and Fuscoboletinus, that are often recognized within Suillus sensu lato, are not monophyletic. Isolates of Suillus granulatus derived from either North America or Europe and Asia are polyphyletic and seem to represent at least two different species. Our data also suggest that within Suillus sensu lato, mycorrhizal associations with Larix are primitive and host changes to Pinus and Pseudotsuga seem to have occurred only once. Changes among host species of the same genus appear to be more frequent. Finally, the most primitive clade within Suillus sensu lato seems to be formed by organisms with a strongly boletinoid hymenophore.

Phylogenetic Implications of rbcL and ITS Sequence Variation in the Berberidaceae

In spite of the use of chromosome number, floral anatomy, pollen morphology, and serology, substantial disagreement remains regarding the systematics of the Berberidaceae. To test competing hypoth- eses about intergeneric relationships in the family, sequences of the chloroplast encoded rbcL gene and ITS regions of the nuclear ribosomal repeat were examined. Analysis of rbcL sequences does not support fragmentation of the Berberidaceae into smaller families, especially the separation of Nandina as a distinct family. The large woody genera, Berberis and Mahonia, are related to the monotypic herbaceous genus Ranzania. Bongardia is nested within a clade characterized by a basic chromosome number of x = 6, and has a remote relationship to the Leontice group with which the genus has been placed in most previous classifica- tions. The x = 6 group, the largest in the Berberidaceae, comprises two distinct lineages: Jeffersonia and the rest of the core genera (Diphylleia, Bongardia, Achlys, and Epimedium). Among the core genera, Diphylleia is sister to Epimedium/Achlys and their sister genus Bongardia. ITS sequence data provided additional support for the phylogenetic relationships of the x = 6 group observed in the rbcL gene tree. Berberidaceae (s.l.) is a heterogeneous assem-

Athelia arachnoidea, the sexual state ofRhizoctonia carotae, a pathogen of carrot in cold storage

Athelia arachnoidea was collected during winter on dead leaves of deciduous trees in Oregon. Minute sclerotia (0.2-1.0 mm) were seen on hyme- nia, whereas in culture sclerotia were much larger (1.0-5.0 mm). The pathogenicity, morphological characteristics, and temperature growth responses of the anamorphic state, were identical to Rhizoctonia carotae. The relationship between the sclerotial ana? morph and the teleomorph was confirmed by DNA sequence of the internal transcribed spacers of the nuclear ribosomal repeat unit. The sequences were homologous among the specimens of A. arachnoidea and the sclerotial anamorph from Oregon, A. arach? noidea and R. carotae isolates from culture collec? tions, and several isolates of R. carotae from carrot cold-storage facilities. Like R. carotae, A. arachnoidea produced abundant crystals of calcium oxalate on the hyphae, was pathogenic on carrot at 3 C, and caused crater rot symptoms equivalent in severity. Sclerotia of A. arachnoidea-R. carotae did not germi? nate under conditions suitable for eruptive germi? nation in A. rolfsii. The DNA sequence of A. epiphylla from Europe was identical (within 6 bp) to A. arach? noidea-R. carotae, whereas A. epiphylla from North America varied by 34-46 independent base pair changes. Athelia epiphylla and A. arachnoidea formed similar sclerotia. Connecting the Rhizoctonia root pathogen to the Athelia teleomorph links the dispa- rate literatures on the natural history of this fungus and reveals significant insights into the epidemiology of the disease. Fibularhizoctonia gen. nov. is proposed to encompass Rhizoctonia species with clamp connec? tions, and the description of R. carotae and R. centri- fuga are emended.

Athelia arachnoidea, the Sexual State of Rhizoctonia carotae, a Pathogen of Carrot in Cold Storage

Athelia arachnoidea was collected during winter on dead leaves of deciduous trees in Oregon. Minute sclerotia (0.2–1.0 mm) were seen on hymenia, whereas in culture sclerotia were much larger (1.0–5.0 mm). The pathogenicity, morphological characteristics, and temperature growth responses of the anamorphic state, were identical to Rhizoctonia carotae. The relationship between the sclerotial anamorph and the teleomorph was confirmed by DNA sequence of the internal transcribed spacers of the nuclear ribosomal repeat unit. The sequences were homologous among the specimens of A. arachnoidea and the sclerotial anamorph from Oregon, A. arachnoidea and R. carotae isolates from culture collections, and several isolates of R. carotae from carrot cold-storage facilities. Like R. carotae, A. arachnoidea produced abundant crystals of calcium oxalate on the hyphae, was pathogenic on carrot at 3 C, and caused crater rot symptoms equivalent in severity. Sclerotia of A. arachnoidea-R. carotae did not germinate under conditions suitable for eruptive germination in A. rolfsii. The DNA sequence of A. epiphylla from Europe was identical (within 6 bp) to A. arachnoidea-R. carotae, whereas A. epiphylla from North America varied by 34–46 independent base pair changes. Athelia epiphylla and A. arachnoidea formed similar sclerotia. Connecting the Rhizoctonia root pathogen to the Athelia teleomorph links the disparate literatures on the natural history of this fungus and reveals significant insights into the epidemiology of the disease. Fibularhizoctonia gen. nov. is proposed to encompass Rhizoctonia species with clamp connections, and the description of R. carotae and R. centrifuga are emended.

THE EVOLUTION OF PARASITISM IN THE RED ALGAE: MOLECULAR COMPARISONS OF ADELPHOPARASITES AND THEIR HOSTS1

ABSTRACTIn several groups of parasites including insect, flowering plant, fungal, and red algal parasites, morphological similarities of the parasites and their specific hosts have led to hypotheses that these parasites evolved from their hosts. But these conclusions have been criticized because the morphological features shared by parasite and host may be the result of convergent evolution. In this study, we examine the hypothesis, originally put forth by Setchell, that adelphoparasitic red algae, that is, parasitic red algae that are morphologically very similar to their hosts, evolved from their specific red algal hosts. Rather than comparing morphological features of parasites and hosts, small‐subunit 18S nuclear ribosomal DNA and the internal transcribed spacer regions (ITSs) of the nuclear ribosomal repeat are compared for five parasites, their hosts, and related nonhosts from four red algal orders. These comparisons reveal that each of these adelphoparasites has evolved either directly from the host on which it is currently found, or it evolved from some other taxon that is closely related to the modern host. The parasites Gardneriella tuberifera, Rhodymeniocolax botryoides, and probably Gracilariophila oryzoides evolved from their respective hosts Sarcodiotheca gaudichaudii, Rhodymenia pacifica, and Gracilariopsis lemaneiformis, respectively. The parasite Faucheocolax attenuata evolved from either Fauchea laciniata or Fauchea fryeana and subsequently radiated onto the other host species. Presently this parasite is found on both hosts. Lastly, some parasitic genera such as Plocamiocolax are polyphyletic in their origins. A species of Plocamiocolax from an Antarctic Plocamium cartilagineum appears to have evolved from its host whereas the common Plocamiocolax pulvinata that occurs along the west coast of North America likely evolved from Plocamium violaceum and radiated secondarily onto its present day host, Plocamium cartilagineum.

Fate of Parasite and Host Organelle DNA during Cellular Transformation of Red Algae by Their Parasites.

The transfer of a nucleus into a cytoplasm of a genetically foreign cell and its subsequent multiplication in the cytoplasm of this cell characterize most parasitic red algal species and their interactions with specific red algal hosts. Nuclei enter the host's cytoplasm upon cell fusion of parasite and host cell; here, they replicate, are spread to contiguous host cells, and ultimately are packaged into spores that reinfect other host thalli. In this study, we examined whether the proplastids and mitochondria that occur in these red algal adelphoparasites are acquired from their host or whether they are unique to the parasite and are brought into the host along with the parasite nucleus. To establish their origins and fates, plastid and mitochondrial restriction fragment length polymorphisms (RFLPs) of parasite cells were compared with those of their host plastid and mitochondrial DNA in three host and parasite pairs. For plastids, no RFLP differences were found between hosts and parasites, supporting an earlier conclusion, based on microscopic studies, that the proplastids of parasites are acquired from their hosts. For mitochondria, characteristic RFLP differences were detected between host and parasite for two of the pairs of species but not for the third. Evidence of the evolutionary difference between hosts and their parasites was shown by RFLP differences between nuclear ribosomal repeat regions.

Chloroplast DNA systematics: a review of methods and data analysis

The field of plant molecular systematics is expanding rapidly, and with it new and refined methods are coming into use. This paper reviews recent advances in experimental methods and data analysis, as applied to the chloroplast genome. Restriction site mapping of the chloroplast genome has been used widely, but is limited in the range of taxonomic levels to which it can be applied. The upper limits (i.e., greatest divergence) of its application are being explored by mapping of the chloroplast inverted repeat region, where rates of nucleotide substitution are low. The lower limits of divergence amenable to restriction site study are being examined using restriction enzymes with 4‐base recognition sites to analyze polymerase chain reaction (PCR)‐amplified portions of the chloroplast genome that evolve rapidly. The comparison of DNA sequences is the area of molecular systematics in which the greatest advances are being made. PCR and methods for direct sequencing of PCR products have resulted in a mushrooming of sequence data. In theory, any degree of divergence is amenable to comparative sequencing studies. In practice, plant systematists have focused on two slowly evolving sequences (rbcL and rRNA genes). More rapidly evolving DNA sequences, including rapidly changing chloroplast genes, chloroplast introns, and intergenic spacers, and the noncoding portions of the nuclear ribosomal RNA repeat, also are being investigated for comparative purposes. The relative advantages and disadvantages of comparative restriction site mapping and DNA sequencing are reviewed. For both methods, the analysis of resulting data requires sufficient taxon and character sampling to achieve the best possible estimate of phylogenetic relationships. Parsimony analysis is particularly sensitive to the issue of taxon sampling due to the problem of long branches attracting on a tree. However, data sets with many taxa present serious computational difficulties that may result in the inability to achieve maximum parsimony or to find all shortest trees.

MOLECULAR DELINEATION OF SPECIES AND SPECIES RELATIONSHIPS IN THE RED ALGAL AGAROPHYTES GRACILARIOPSIS AND GRACILARIA (GRACILARIALES)1

ABSTRACTDelineation of species in the economically important agarophyte genera Gracilaria and Gracilariopsis has proven extremely difficult using available morphological characteristics. In this study, we examine the usefulness of two transcribed spacers for molecular systematic studies of these genera. The polymerase chain reaction was used to amplify the internal transcribed spacers (ITSs) and the intervening 5.8S ribosomal DNA of the nuclear ribosomal repeat region. In addition, a plastid spacer region and flanking regions of coding genes were amplified from the RUBISCO operon. Both regions were sequenced for individuals and populations of Gracilariopsis lemaneiformis (Bory) Dawson, Acleto, et Foldvik to determine the usefulness of these spacers in delimiting populations. These studies reveal that there is as much variation among individuals of a population as there is between individuals of geographically separate populations. In addition, the ITS spacer regions were compared between different species of Gracilariopsis and Gracilaria. The nuclear ITS spacer region is conserved at a species level in both genera and provides phylogenetically informative characters that can be used to examine species interrelationships among relatively closely related taxa. However, because of the difficulties of aligning this entire region among species from the two genera, the ITS region is not useful for examining intergenera relationships. ITS interspecies sequence comparisons indicate that Gracilariopsis lemaneiformis from California is significantly different from G. lemaneiformis from China and that a species of Gracilariopsis from Peru is more closely related to G. lemaneiformis from North Carolina than it is to the other Gracilariopsis species examined. In addition, these studies indicate that Gracilaria chilensis Bird, McLachlan, et Oliveira from New Zealand and Gracilaria tenuistipitata Chang et Xia from southeast Asia are as closely related as are Gracilaria verrucosa (Hudson) Papenfuss, G. pacifica Abbott, and Gracilaria robusta Kylin. Phylogenetic analysis of aligned plastid spacer sequences from Gracilaria and Gracilariopsis taxa provide similar conclusions about species relationships.

MOLECULAR DELINEATION OF SPECIES AND SYNGENS IN VOLVOCACEAN GREEN ALGAE (CHLOROPHYTA)1

ABSTRACTTwo species of the colonial green flagellate family Volvocaceae are worldwide in distribution yet exhibit contrasting species structure. Geographically disparate isolatesof Gonium pectoraleMueller can interbreed while isolates ofPandorina morumBory behave quite differently. More than 20 sexually isolated subpopulations occur within this species; these have been termed “syngens” (sensu Sonneborn). Because prezygotic barriers to mating cause intersyngen pairings to fail, breeding analyses cannot be used to estimate genetic relatedness among the syngens of P.morum.DNA comparisons provide an alternative method of assessing genetic relatedness. We compared the nucleotide sequence of the internal transcribed spacer (ITS) region of the nuclear ribosomal repeat among clones of P.morumand ofG. pectorale.Members of syngens ofP. morumwith distribution restricted to one small geographical area show great similarity. Likewise, members of any syngen of worldwide distribution show near uniformity, even those from different continents. However, the ITS sequence of each syngen differs from that of other syngens. In contrast,G. pectorale, which has an ITS region that is remarkably uniform throughout the world, appears to consist of a single syngen within North America and Europe by mating tests. The molecular data are in complete conformity with previous syngen assignment. Because the latter is based on mating affinity, with two complementary mating types per syngen, the evolution of new mating type pairs appears to be the basis of microevolution in these algae. We infer that eitherP. morumis a more ancient species thanG. pectoraleor thatP. morumhas a less stable genome. In either case, the biogeographic distribution of certain syngens may reflect climatological changes of the past.

ITS primers with enhanced specificity for basidiomycetes ‐ application to the identification of mycorrhizae and rusts

We have designed two taxon-selective primers for the internal transcribed spacer (ITS) region in the nuclear ribosomal repeat unit. These primers, ITS1-F and ITS4-B, were intended to be specific to fungi and basidiomycetes, respectively. We have tested the specificity of these primers against 13 species of ascomycetes, 14 of basidiomycetes, and 15 of plants. Our results showed that ITS4-B, when paired with either a 'universal' primer ITS1 or the fungal-specific primer ITS1-F, efficiently amplified DNA from all basidiomycetes and discriminated against ascomycete DNAs. The results with plants were not as clearcut. The ITS1-F/ITS4-B primer pair produced a small amount of PCR product for certain plant species, but the quantity was in most cases less than that produced by the 'universal' ITS primers. However, under conditions where both plant and fungal DNAs were present, the fungal DNA was amplified to the apparent exclusion of plant DNA. ITS1-F/ITS4-B preferential amplification was shown to be particularly useful for detection and analysis of the basidiomycete component in ectomycorrhizae and in rust-infected tissues. These primers can be used to study the structure of ectomycorrhizal communities or the distribution of rusts on alternate hosts.

Five major nuclear ribosomal repeats represent a large and variable fraction of the genomic DNA of Picea rubens and P. mariana.

The nuclear ribosomal repeats for the 18S, 5.8S, and 26S RNAs of two closely related Picea (spruce) species were characterized by restriction mapping and Southern blot hybridization. Restriction polymorphisms were identified in the IGS and ITS sequences; however, no polymorphism was species specific. As many as five different rDNA repeat units were observed in individual genomes. The repeat size for these gymnosperms ranged from a minimum of 32 kbp to greater than 40 kbp, two- to threefold larger than the typical angiosperm rDNA unit. Slot-blot hybridizations were used to determine the nuclear rDNA copy concentration. Among P. rubens individuals threefold variation was observed in the rDNA copy concentration, and among P. mariana individuals such variation was as much as sixfold. At a size greater than 32 kbp and at a concentration averaging 1.2-1.3 x 10(4) copies/pg, the rDNA constitutes approximately 4% of the total genome. Regression analysis revealed a significant relationship between copy concentration of the rDNA repeat unit in P. rubens and geographic origins. Differences in the rDNA content in Picea could contribute to the variation, in overall genome size, that has been observed within conifer species.

Identification of indigenous and introduced symbiotic fungi in ectomycorrhizae by amplification of nuclear and mitochondrial ribosomal DNA

We used the polymerase chain reaction (PCR) to amplify specific regions of the nuclear and mitochondrial genomes of fungi using DNA extracted from pure cultures as well as that directly from ectomycorrhizal rootlets. The internal transcribed spacer (ITS) of the nuclear ribosomal repeat unit and a portion of the mitochondrial large subunit ribosomal RNA gene were chosen as target sequences because both exist in high copy number and amplification primers for both discriminate between plant and fungal DNAs. These features provided a sensitivity and specificity sufficient for detection and analysis of a single mycorrhizal rootlet. We evaluated the variations in the amplified products with regard to the length, restriction endonuclease sites, and primary sequence for use in identification of genera, species, and strains of ectomycorrhizal fungi, with particular attention to selected Laccaria species. Accidental contamination of jack pine seedlings by Telephora terrestris was easily recognized. Amplification and direct DNA sequencing of a portion of the ITS were done for three strains of L. bicolor, one of L. laccata, one of L. proximo, and one of T. terrestris. The nucleotide sequence variation was 32% between L. bicolor and T. terrestris, and it ranged from 3 to 5% among the three Laccaria species examined and from 1 to 2% within L. bicolor. The degree of variation observed is sufficient to allow the use of specific oligonucleotides to characterize amplified ITS products. To demonstrate the feasibility of this approach we designed and tested a probe that enabled two isolates of L. bicolor to be distinguished by a single base-pair difference in a filter-based hybridization assay. In combination these methods now provide an important set of tools for the study of mycorrhizal ecology. Key words: internal transcribed spacer, LrDNA gene, mycorrhizal ecology, polymerase chain reaction, rDNA.

Multiple origins of polyploids in the Glycine tabacina complex inferred from chloroplast DNA polymorphism.

The Glycine tabacina polyploid complex has been shown to include a minimum of two morphological and crossing groups, which also differ in chloroplast DNA (cpDNA) restriction map and nuclear ribosomal gene repeat phenotype. These AAB2B2 and BBB2B2 G. tabacina polyploids contain plastomes referable to the A and B diploid plastome groups of subgenus Glycine, respectively. Eight different cpDNA variants were observed among the 65 B-type polyploids studied, six of which were identical for numerous restriction site characters to plastome types found among the highly polymorphic B genome diploid species. It is hypothesized that there have been numerous independent origins of polyploid G. tabacina: at least one AA x B2B2 event and a minimum of five BB x B2B2 events involving different BB types as female progenitor. Low amounts of cpDNA divergence between diploid and polyploid plastomes and among the plastomes of geographically disjunct polyploids suggest that the origin and dispersal of polyploids are relatively recent events. All hypothesized diploid progenitors are native to Australia, while both A- and B-type G. tabacina polyploids occur on islands of the Pacific outside the range of diploids. The presence of several different plastome types of polyploid G. tabacina in the Pacific islands suggests that several colonization events have occurred.