NATURAL HYBRIDIZATION BETWEEN PHLOX MACULATA AND PHLOX GLABERRIMA AND ITS EVOLUTIONARY SIGNIFICANCE

Levin, 1). A. (U. Illinois, Urbana.) Natural hybridization between Phlox maculata and Phlox glaberrima and its evolutionary significance. Amer. Jour. Bot. 50(7): 714–720. Illus. 1963.—Field and herbarium studies indicate that Phlox maculata ssp. pyramidalis is similar to P. glaberrima ssp. interior in a number of characteristics. A hybrid swarm involving P. maculata ssp. maculata and P. glaberrima ssp. interior was discovered which contained some plants that were almost identical to P. maculata ssp. pyramidalis. Crosses between P. maculata and P. glaberrima indicate that the 2 species cross readily. The chromosome complements of the 2 species are morphologically similar. These data suggest that P. maculata ssp. pyramidalis is a stabilized introgressant type.     

PHYSIOLOGICAL EVIDENCE OF HYBRIDIZATION AND RETICULATE EVOLUTION IN PHLOX MACULATA

A comparative physiological analysis was conducted on a hybrid swarm involving P. maculata subsp. maculata and P. glaberrima subsp. interior. The population contained an array of segregates and introgressants. Hybrids displayed a high degree of heterogeneity in their physiological attributes, some characters being intermediate to, similar to, or transgressing those of the parental taxa. For example, both net photosynthetic rates and net photosynthetic/dark respiratory ratios were enhanced in the hybrids, and the level of enhancement was associated with the level of morphological intermediacy. Conversely, no enhancement was noted in either respiration rates or foliar fresh weight/ovendry weight ratios of the hybrids. Because of physiological imbalance, about one-third of the hybrids were eliminated early in their development. Representatives of P. maculata subsp. pyramidalis, a putative stabilized derivative of hybridization between the above two parental species, were intermediate in most physiological features and closely resembled some natural hybrids. The data verify that the physiological features of subspecies pyramidalis can be assembled through recombination of the P. maculata and P. glaberrima genomes.     

RETICULATE EVOLUTION IN PHLOX AS SEEN THROUGH PROTEIN ELECTROPHORESIS

Seed protein profiles were used to document the genome constitutions of seven Phlox taxa believed to be stabilized derivatives of hybridization between P. pilosa and P. carolina, P. drummondii or P. amoena. These species have very distinctive seed protein profiles. Analyses of profiles from these and other phloxes not involved in the reticulum (P. maculata, P. glaberrima and their hybrid derivative P. maculata subsp. pyramidalis) demonstrated that profile components are inherited as co-dominant units, alteration of ploidal level does not alter the profile, profile components may undergo segregation and recombination, and profile components in hybrids do not re-combine in vivo or in vitro to produce new proteins. The putative derivatives of hybridization between P. pilosa and P. carolin, i.e., P. pilosa subsp. detonsa, P. pilosa subsp. sangamonensis, P. floridana and P. pulcherrima, display protein profiles which are nearly summations of the parental patterns as do the putative derivatives of P. pilosa and P. drummondii. i.e., P. villosissima and P. aspera. The putative derivative of P. pilosa and P. amoena, i.e., P. pilosa subsp. deamii, displays a completely additive profile. Genome constitutions judged from morphological, cytological, and chromatographical data are fully corroborated by the protein profiles.     

Evolutionary history of the Dactylorhiza maculata polyploid complex (Orchidaceae)

Taxonomic complexity may be associated with migration history and polyploidy. We used plastid and nuclear DNA markers to investigate the evolutionary history of the systematically challenging Dactylorhiza maculata polyploid complex. A total of 1833 individuals from 298 populations from throughout Europe were analysed. We found that gene flow was limited between the two major taxa, diploid ssp. fuchsii (including ssp. saccifera) and tetraploid ssp. maculata. A minimum of three autotetraploid lineages were discerned: (1) southern/western ssp. maculata; (2) northern/eastern ssp. maculata; and (3) Central European ssp. fuchsii. The two ssp. maculata lineages, which probably pre‐date the last glaciation, form a contact zone with high genetic diversity in central Scandinavia. Intermediate plastid haplotypes in the contact zone hint at recombination. Central Europe may have been a source area for the postglacial migration for the southern/western lineage of ssp. maculata, as well as for ssp. fuchsii. The northern/eastern lineage of ssp. maculata may have survived the LGM in central Russia west of the Urals. The tetraploid lineage of ssp. fuchsii is indistinguishable from diploid ssp. fuchsii, and is probably of postglacial origin. The Mediterranean region and the Caucasus have not contributed to the northward migration of either ssp. fuchsii or ssp. maculata. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 503–525.     

Antiproliferative effects of essential oils and their major constituents in human renal adenocarcinoma and amelanotic melanoma cells

Abstract. Objectives: The purpose of this study was to evaluate cytotoxic activity of Platycladus orientalis, Prangos asperula and Cupressus sempervirens ssp. pyramidalis essential oils and to identify active components involved in inhibition of population growth of human cancer cell lines. Materials and methods: Essential oils were obtained by hydrodistillation and were analysed by gas chromatography and gas chromatography coupled to mass spectrometry. Antiproliferative activity was tested on amelanotic melanoma C32 cells and on renal cell adenocarcinoma cells, using the sulphorhodamine B assay. Results: Cupressus sempervirens ssp. pyramidalis leaf oil exerted the highest cytotoxic activity with an IC₅₀ value of 104.90 µg/mL against C32, followed by activity of P. orientalis and P. asperula on the renal adenocarcinoma cell line (IC₅₀ of 121.93 and 139.17 µg/mL, respectively). P. orientalis essential oil was also active against amelanotic melanoma with an IC₅₀ of 330.04 µg/mL. Three identified terpenes, linalool, β‐caryophyllene and α‐cedrol, were found to be active on both cell lines tested. Conclusions: Our findings provide novel insights into the field of cytotoxic properties of essential oils. This study provided evidence on how cytotoxic activity of the oils is not always related to their major constituents, except for lower activity found in both cell lines for α‐cedrol. Interestingly, β‐caryophyllene and linalool exhibited comparable IC₅₀ values to the commercial drug vinblastine on the ACHN cell line. This opens a new field of investigation to discover mechanisms responsible for the observed activity.     

Assessing hybrid sterility in <Emphasis Type="Italic">Oryza glaberrima</Emphasis> × <Emphasis Type="Italic">O. sativa</Emphasis> hybrid progenies by PCR marker analysis and crossing with wide compatibility varieties

Interspecific crossing of the African indigenous rice Oryza glaberrima with Oryza sativa cultivars is hindered by crossing barriers causing 100% spikelet sterility in F₁ hybrids. Since hybrids are partially female fertile, fertility can be restored by back crossing (BC) to a recurrent male parent. Distinct genetic models on spikelet sterility have been developed predicting, e.g., the existence of a gamete eliminator and/or a pollen killer. Linkage of sterility to the waxy starch synthase gene and the chromogen gene C, both located on chromosome 6, have been demonstrated. We selected a segregating BC₂F₃ population of semi-sterile O. glaberrima × O. sativa indica hybrid progenies for analyses with PCR markers located at the respective chromosome-6 region. These analyses revealed that semi-sterile plants were heterozygous for a marker (OSR25) located in the waxy promoter, whereas fertile progenies were homozygous for the O. glaberrima allele. Adjacent markers showed no linkage to spikelet sterility. Semi-sterility of hybrid progenies was maintained at least until the F₄ progeny generation, suggesting the existence of a pollen killer in this plant material. Monitoring of reproductive plant development showed that spikelet sterility was at least partially due to an arrest of pollen development at the microspore stage. In order to address the question whether genes responsible for F₁ sterility in intraspecific hybrids (O. sativa indica × japonica) also cause spikelet sterility in interspecific hybrids, crossings with wide compatibility varieties (WCV) were performed. WCV accessions possess "neutral" S-loci (Sⁿ) improving fertility in intraspecific hybrids. This experiment showed that the tested Sⁿ-loci had no fertility restoring effect in F₁ interspecific hybrids. Pollen development was completely arrested at the microspore stage and grains were never obtained after selfing. This suggests that distinct or additional S-loci are responsible for sterility of O. glaberrima × O. sativa hybrids.Communicated by H.C. Becker     

NOVEL FLAVONOIDS AND RETICULATE EVOLUTION IN THE PHLOX PILOSA–P. DRUMMONDII COMPLEX

The nonanthocyanin flavonoids of the diploids Phlox pilosa ssp. pilosa and P. drummondii ssp. mcallisteri and their putative allotetraploid derivatives P. aspera and P. villosissima were characterized by chromatographic and spectrophotometric analyses. Synthetic F₁ diploid hybrids were also examined. All but one of the compounds encountered were glycoflavone (C-glycosyl) derivatives of either apigenin or luteolin. Although some compounds were present in all four taxa, most were species-specific. Together, the diploids exhibited 15 different flavonoids. Half of each tetraploid ensemble was composed of novel flavonoids, compounds not manifest in either diploid ancestor. In total, the tetraploids produced seven different novel flavonoids. Five novel compounds differed from particular diploid compounds only in number or kind of oxygen-linked sugar substituents. Ostensibly, these five are either identical to diploid biosynthetic intermediates or share common precursors with related diploid end products. The mode of origin of all novel compounds is discussed.     

VARIATIONS IN POLYMNIA POLLEN

Photomicrographs of normal and aberrant Polymnia (Compositae) pollen were made with the scanning electron microscope and with the light microscope. Anomalous pollen forms from F₁ hybrids of P. maculata Cav. are compared to the parental type and to the closely related P. uvedalia (L.) L. Among the variations discussed are differences in size and form, fused aggregates, and reduction in length of spines. The cause of these variations is unknown, although similar anomalies were later found in a single P. maculata parent, Wells No. 740, which grew under similar standard greenhouse conditions.     

Habitat differentiation, hybridization and gene flow patterns in mixed populations of diploid and autotetraploid Dactylorhiza maculata s.l. (Orchidaceae)

Detailed ecological, morphological and molecular analyses were performed in mixed populations of diploid and autotetraploid Dactylorhiza maculata s.l. in Scandinavia. Comparisons were made with pure populations of either diploid ssp. fuchsii or tetraploid ssp. maculata. It was shown that mixed populations are the result of secondary contact between ssp. fuchsii and ssp. maculata. No patterns of recent and local autopolyploidization were found. Morphology and nuclear DNA markers (internal transcribed spacers of nuclear ribosomal DNA) showed that diploids and tetraploids from mixed populations have similar levels of differentiation to diploids and tetraploids from pure populations. Vegetation analyses, as well as analyses of environmental variables, revealed that diploid and tetraploid individuals in mixed populations are ecologically well differentiated on a microhabitat level. Diploids and tetraploids in pure populations have wider ecological amplitudes than they do in mixed populations. Triploid hybrids grew in intermediate microhabitats between diploids and tetraploids in the mixed populations. Plastid DNA markers indicated that both diploids and tetraploids may act as the maternal parent. Based on morphology and nuclear markers triploids are more similar to tetraploids than to diploids. There were indications of introgressive gene flow between ploidy levels. Plastid markers indicated that gene flow from diploid to tetraploid level is most common, but nuclear markers suggested that gene flow in opposite direction also may occur. Similar patterns of differentiation and gene flow appeared in localities that represented contrasting biogeographic regions. Disturbance and topography may explain why hybridization was slightly more common and the differentiation patterns somewhat less clear in the Scandinavian mountains than in the coastal lowland. An erratum to this article can be found at     

Cold tolerance of invasive freshwater snails,Pomacea canaliculata,P. maculata,and their hybrids helps explain their different distributions

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Systematics and phylogeography of the Dactylorhiza maculata complex (Orchidaceae) in Scandinavia: insights from cytological, morphological and molecular data

Flow cytometry, morphometry and molecular markers [plastid DNA and internal transcribed spacers (ITS) of nuclear ribosomal DNA] were used to determine taxonomic and phylogeographic patterns in Dactylorhiza maculata s.l. from Scandinavia. A total of 238 individuals from 27 populations from throughout all of Scandinavia, including the adjacent Kola Peninsula of Russia, were analyzed. Diploid D. maculata ssp. fuchsii and autotetraploid D. maculata ssp. maculata are morphologically differentiated. Fragment size variants from 10 plastid DNA loci (seven microsatellite loci and three loci with indel variation) were combined to give 43 haplotypes. Three major groups of haplotypes were found. Group I haplotypes were prevalent in the north and the northeast, whereas Group II haplotypes were prevalent in the south and the southwest. Group III was represented by only a single haplotype and appeared to be the result of introgression from D. incarnata s.l. Group I and Group II haplotypes did not correspond with cytologically and morphologically defined D. maculata ssp. fuchsii or D. maculata ssp. maculata. Past introgressive gene flow rather than recent hybridization is envisaged. Intermediate Group I haplotypes between Group II and the rest of Group I were detected in a zone of contact in central Sweden, which may suggest plastid DNA recombination. The six ITS alleles scored showed strong positive correlation with taxonomy. All data sets obtained for ssp. maculata were significantly correlated with geography. Three different autotetraploid lineages are hypothesized. One lineage may represent postglacial immigration from the south and the other two lineages may represent eastern immigration routes. Morphology and ITS data suggested that subarctic populations of ssp. maculata should be recognized as var. kolaënsis.     

Patterns of cryptic hybridization revealed using an integrative approach: a case study on genets (Carnivora, Viverridae, Genetta spp.) from the southern African subregion

Recent years have seen the development of molecular‐based methodologies to investigate hybridization and its impact on the evolutionary process. However, morphological characterization of hybrid zones has only scantily been considered, especially in zootaxa. Thus, the level of congruence between molecular and morphological characters when attempting to detect hybrids remains a poorly tackled area. The genets (genus Genetta) provide an ideal case study for further investigation of the respective contribution of morphology and DNA in hybrid zone characterization because (1) their morphology has recently been exhaustively explored and (2) the existence of hybrid zones in southern Africa was proposed in the literature. We assessed levels of hybridization among the southern African genets, and questioned the role of ecological factors on the hybridization patterns detected. We used an integrative approach involving nine discrete morphological characters and a diagnostic discriminant function, geometric morphometrics and sequences of cytochrome b including collection specimens. The combination of independent materials allowed us to accurately reassess the level of hybridization in southern African genets, and revealed cryptic, interspecific gene flows. Morphology unambiguously detected a low number of G. maculata × G. tigrina hybrids and rejected the hypothesis of a large intergradation zone in KwaZulu‐Natal, thus supporting the species status of the two genets. Cytochrome b analyses revealed: (1) cryptic, massive hybridization between G. tigrina and the sympatric G. felina, and (2) a trace of reticulation (one sequence) between G. tigrina and the allopatric G. genetta. The type specimen of G. mossambica Matschie, 1902 is considered to be a morphological hybrid between G. maculata and G. angolensis. Remarkably, the morphological approaches (discrete characters and morphometrics) proved complementary to conclusions derived from cytochrome b sequences. Whilst morphometrics was generally unable to accurately identify all putative hybrids, this approach revealed diagnostic cranial shape differences between recognized species as well as the cryptic G. ‘letabae’ (included in the super‐species G. maculata). Morphometrics also confirmed the diagnostic value and age dependency of discrete characters. Our integrative approach appeared necessary to the detection of cryptic hybridizations and to the comprehensive characterization of hybrid zones. The recurrent detection of hybrids exhibiting tigrina‐like coat patterns may suggest (1) asymmetric hybridization of G. tigrina males to females of other species and (2) positive selection for tigrina‐like phenotype in South African habitats, but these hypotheses will have to be further tested using other sources of evidence. Despite the precise mosaic of hybrid zones identified in southern African genets, the environmental factors that shape patterns of distribution of hybrids remain unclear. Nevertheless, in the light of our range reassessment, it appears that seasonality of precipitation and periods of annual frost may play stringent roles in the distribution of genets. The complementarity of our results based on morphology and molecules is regarded as encouraging for the further development of integrative approaches in order to better understand the complex phenomena that underlie hybridization processes. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 86 , 11–33.     

Processes Underpinning Development and Maintenance of Diversity in Rice in West Africa: Evidence from Combining Morphological and Molecular Markers

We assessed the interplay of artificial and natural selection in rice adaptation in low-input farming systems in West Africa. Using 20 morphological traits and 176 molecular markers, 182 farmer varieties of rice (Oryza spp.) from 6 West African countries were characterized. Principal component analysis showed that the four botanical groups (Oryza sativa ssp. indica, O. sativa ssp. japonica, O. glaberrima, and interspecific farmer hybrids) exhibited different patterns of morphological diversity. Regarding O. glaberrima, morphological and molecular data were in greater conformity than for the other botanical groups. A clear difference in morphological features was observed between O. glaberrima rices from the Togo hills and those from the Upper Guinea Coast, and among O. glaberrima rices from the Upper Guinea Coast. For the other three groups such clear patterns were not observed. We argue that this is because genetic diversity is shaped by different environmental and socio-cultural selection pressures. For O. glaberrima, recent socio-cultural selection pressures seemed to restrict genetic diversity while this was not observed for the other botanical groups. We also show that O. glaberrima still plays an important role in the selection practices of farmers and resulting variety development pathways. This is particularly apparent in the case of interspecific farmer hybrids where a relationship was found between pericarp colour, panicle attitude and genetic diversity. Farmer varieties are the product of long and complex trajectories of selection governed by local human agency. In effect, rice varieties have emerged that are adapted to West African farming conditions through genotype × environment × society interactions. The diversity farmers maintain in their rice varieties is understood to be part of a risk-spreading strategy that also facilitates successful and often serendipitous variety innovations. We advocate, therefore, that farmers and farmer varieties should be more effectively involved in crop development.     

Genetic diversity and domestication history of African rice (<Emphasis Type="Italic">Oryza glaberrima</Emphasis>) as inferred from multiple gene sequences

Nucleotide variation in 14 unlinked nuclear genes was investigated in species-wide samples of African rice (Oryza glaberrima) and its wild progenitor (O. barthii). Average estimates of nucleotide diversity were extremely low in both species (θ _sil = 0.0007 for O. glaberrima; θ _sil = 0.0024 for O. barthii). About 70% less diversity was found in O. glaberrima than in its progenitor O. barthii. Coalescent simulation indicated that such dramatic reduction of nucleotide diversity in African rice could be explained mainly by a severe bottleneck during its domestication. The progenitor of African rice maintained also low genetic diversity, which may be attributed to small effective population size in O. barthii. Self-pollinating would be another factor leading to the unusually low diversity in both species. Genealogical analyses showed that all O. glaberrima accessions formed a strongly supported cluster with seven O. barthii individuals that were sampled exclusively from the proposed domestication centers of African rice. Population structure and principal component analyses found that the O. glaberrima group was homogeneous with no obvious genetic subdivision, in contrast to the heterogeneous O. barthii cluster. These findings support a single domestication origin of African rice in areas of the Upper Niger and Sahelian Rivers.     

Identification of QTLs for Drought-Related Traits in Alien Introgression Lines Derived from Crosses of Rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> cv. IR64) × <Emphasis Type="Italic">O. glaberrima</Emphasis> under Lowland Moisture Stress

Drought is a major abiotic stress that limits rice productivity in rain-fed and upland ecosystems. African rice, Oryza glaberrima, has low yields but is tolerant to drought and other stresses. We evaluated 513 BC₂F₃ progenies from alien introgression lines (AILs) that were derived from crosses of Oryza sativa (IR64) × O. glaberrima. They were assessed for yield and other traits when grown under drought at two locations. Such conditions reduced grain production by 59% compared with the recurrent parent (IR64). However, 33 AILs had higher yields, thus demonstrating their potential as genetic material for transferring drought-related traits from O. glaberrima to O. sativa. A set of 200 AILs was selectively genotyped with 173 simple sequence repeat and sequenced tagged site markers. Molecular analysis showed that a mean of 4.5% of the O. glaberrima genome was introgressed in BC₂F₃ AILs. Our analysis revealed 33 quantitative trait loci (QTLs; including 10 novel) for different traits. O. glaberrima contributed 50% of the alleles to those newly identified QTLs, with one for grain yield per plant (ypp9.1) being new. A QTL at RM208 on chromosome 2 positively affected yield under stress, accounting for 22% of the genetic variation. Our identification of drought-related QTLs for yield and yield components will be useful to future research efforts in marker-assisted selection.     

A combined barcode and morphological approach to the systematics and biogeography of Laurencia pyramidalis and Laurenciella marilzae (Rhodophyta)

In the present study we undertook an integrative approach, using both morphological and molecular data (COI-5P + rbcL), to assess the presence of Laurencia pyramidalis in Lusitanian Macaronesia. We studied type material of L. pyramidalis from the herbarium of the Naturalis Biodiversity Center, the Netherlands, and designated a lectotype and syntypes. Vegetative and reproductive features of L. pyramidalis were observed and we included a specimen from the type locality in our molecular analyses. We also investigated the geographical distribution of Laurenciella marilzae, a species recently described from the Canary Islands. Barcode sequences (COI-5P and rbcL) were generated for L. pyramidalis from the type locality (Normandy, France), the Azores, Madeira and the Canary Islands, and for L. marilzae from its type locality (Tenerife, Canary Islands), the Azores and Brazil.     

A first interspecific Oryza sativa×Oryza glaberrima microsatellite-based genetic linkage map

Oryza glaberrima is an endemic African cultivated rice species. To provide a tool for evaluation and utilisation of the potential of O. glaberrima in rice breeding, we developed an interspecific O. glaberrima×Oryza sativa genetic linkage map. It was based on PCR markers, essentially microsatellites and STSs. Segregation of markers was examined in a backcross (O. sativa/O. glaberrima//O. sativa) population. Several traits were measured on the BC₁ plants, and major genes and QTLs were mapped for these traits. Several of these genes correspond well to previously identified loci. The overall map length was comparable to those observed in indica×japonica crosses, indicating that recombination between the two species occurs without limitation. However, three chromosomes show discrepancies with the indica×japonica maps. The colinearity with intraspecific maps was very good, confirming previous cytological observations. A strong segregation-distortion hot spot was observed on chromosome 6 near the waxy gene, indicating the presence of s ₁₀ , a sporo-gametophytic sterility gene previously identified by Sano (1990). The main interests of such a PCR-based map for African rice breeding are discussed, including gene and QTL localisation, marker-assisted selection, and the development of interspecific introgression lines. Received: 1 June 1991 / Accepted: 22 June 1999     

The influence of hybridization on epidermal properties of birch species and the consequences for palaeoclimatic interpretations

The Fennoscandian birch population primarily consists of Betula nana, B. pendula and B. pubescens ssp. czerepanovii, the Mountain birch. Frequent hybridization between the Mountain birch and B. nana generates a wide range of genotypic and phenotypic plasticity in the subarctic birch zone of Fennoscandia. Phases of subarctic conditions prevailed during the Late Glacial in large parts of NW Europe, and palynological as well as macrofossil analysis provide some evidence for the occurrence of birch hybrids during these intervals. Leaves from genetically controlled specimens of Betula pendula, B. pubescens ssp. czerepanovii, B. nana and the hybrids B. pubescens ssp. czerepanovii × nana and B. nana × pubescens ssp. czerepanovii are investigated for their specific characteristics of the epidermis morphology. Frequency and size of epidermal cells and stomata reveal a close affinity of both hybrids to B. nana and allow a differentiation of the intermediate forms between B. nana and the Mountain birch. With respect to palaeoatmospheric CO₂ reconstructions based on stomatal index, epidermal analysis shows that a possible occurrence of hybrids in fossil leaf assemblages has no profound consequences for combined species records. However, the significant differences observed in B. nana demand the separation of this species. A comparison of the cuticle properties of B. pendula and B. pubescens from Finnish Lapland and leaf material from The Netherlands reveals a divergence of the stomatal index that may be due to differences in day light length.     

A biosystematic study of the Interiores species group of the genus Vernonia (Compositae)

The taxa of the Interiores species group are treated as two species, one of which is divided into two subspecies.Vernonia missurica, a widespread taxon, has large flower heads (32-58 flowers per head), obtuse involucral bract tips, and a characteristic flavonoid Chromatographic profile.Vernonia baldwinii ssp.baldwinii, occurring throughout the Ozarks and Ouachitas, andV. baldwinii ssp.interior of the Central Plains possess smaller flower heads (17-34 flowers per head), acute or acuminate involucral bracts, and a different Chromatographic profile.Vernonia baldwinii ssp.baldwinii is distinguished from ssp.interior by the recurved involucral bract tips and by the possession of more flowers per head. Morphological data reveal that an intergradation zone exists between the population systems of the two subspecies along the edges of the Ozarks and Ouachitas. Although much gene exchange occurs between these two taxa, they maintain a level of genetic integrity that permits their ready recognition throughout wide ranges. All three taxa have a gametic chromosome number ofn = 17 and hybridize extensively with sympatric species.     

Conservation of genetic diversity in British populations of the diploid endemic Coincya monensis ssp monensis (Isle of Man Cabbage): the risk of hybridisation with the tetraploid alien, Coincya monensis ssp cheiranthos

Coincya monensis is represented in the British flora by two, cytologically distinct subspecies. Coincya monensis ssp monensis is an endemic diploid with a coastal sand dune distribution that includes a number of isolated populations. Coincya monensis ssp cheiranthos is a tetraploid alien, well established in South Wales in early successional habitats. Both subspecies share similar life form traits, flowering times and pollinators. Cluster analysis and phylogenetic reconstruction based on sequences of the mitochondrial nad4 gene confirmed the distinction between alien and endemic taxa. Tetraploid populations carry more polymorphic RAPDs loci and their genetic diversity is partitioned more within than among populations. In contrast, C. monensis ssp monensis has a distinct population genetic structure. Analysis of the multilocus genetic data confirmed a structure of genetically isolated, endemic population clusters in Scotland, Arran, the Isle of Man and South Wales. Experimental hybridisation showed the two subspecies are interfertile. Multivariate analysis of RAPDs data resolved hybrids between alien and endemic clusters and hybrids contained a proportion of alien-specific polymorphic loci. Hybrids of alien maternal parentage contained the mitochondrial nad4 sequence characteristic of the alien subspecies. Since the alien subspecies can invade mobile sand dune communities from urban sites and compete for pollinators, there is a risk that alien and endemic populations will mix and introgress. Conservation of endemic genetic diversity in Britain will require protection for all C. monensis ssp monensis populations. Currently, the most disjunct endemic population in South Wales is most at risk from introgression.