Evidence of hybridization between Lythrum salicaria (purple loosestrife) and L. alatum (winged loosestrife) in North America

BACKGROUND AND AIMS: Although Lythrum salicaria (purple loosestrife) was introduced to North America from Europe in the early 1800s, it did not become invasive until the 1930s. Whether hybridization with L. alatum (winged loosestrife) could have played a role in its ultimate spread was tested. METHODS: Six diagnostic morphological traits (flower number per axil, leaf placement, calyx pubescence, style type, plant height and leaf shape) were surveyed in 30 populations of Lythrum across eastern North America. Patterns of AFLP variation were also evaluated using five primer pairs in a 'global screen' of the same North American populations of L. salicaria and L. alatum described above, in L. salicaria from 11 European populations located in Germany, England, Ireland, Austria and Finland, and in six L. salicaria cultivars. KEY RESULTS: All of the North American L. salicaria populations had individuals with alternate leaf placement and 1-2 flowers per leaf axil, which have not been described in Eurasian L. salicaria but predominate in North American L. alatum. In addition, two L. salicaria populations were intermediate in height and leaf ratio between the typical L. salicaria and L. alatum populations in their native fields and when grown in a common greenhouse. In screens of variation patterns using 279 AFLPs, only two fragments were found that clearly supported introgression from L. alatum to L. salicaria. CONCLUSIONS: The evidence indicates that L. salicaria may have hybridized with L. alatum, but if so, only a small fraction of L. alatum genes have been retained in the genome of L. salicaria. This is unlikely to have led to a dramatic adaptive shift unless the introgression of a few key genes into L. salicaria stimulated a genomic reorganization. It is more likely that crossing among genotypes of L. salicaria from multiple introductions provided the necessary variability for new adaptations to arise.     

Isozyme characterization of genetic diversity in Minnesota populations of purple loosestrife,Lythrum salicaria (lythraceae)

Starch gel electrophoresis of plant proteins was used to identify purple loosestrife (Lythrum spp.) cultivars and weedy populations. Preliminary determinations were made as to what degree weedy loosestrife populations were related (or genetically similar) to populations of L. alatum, L. virgatum, and horticultural cultivars. Cluster analysis of the data indicated that native L. alatum was genetically different from all populations of purple loosestrife and cultivars examined. The L. salicaria and L. virgatum cultivars, as groups, were not genetically distinguishable from the weedy populations analyzed. Seven cultivars of L. salicaria origin analyzed as a group were not distinguishable from the eight cultivars of L. virgatum origin, indicating that separation by cultivar origin may not be feasible. While the two “groups” were not distinguishable, most individual cultivars could be distinguished from one another by isozyme phenotype. Genetic variation was high within populations of weedy purple loosestrife but low among populations, which is characteristic of polyploid, perennial plant species that are widely distributed. Geographic location did not consistently correlate with genetic similarity.     

The effect of a water gradient on the vesicular-arbuscular mycorrhizal status of Lythrum salicaria L. (purple loosestrife)

 The mycorrhizal status of Lythrum salicaria (Lythraceae) was assessed under growth room and field conditions. Growth room studies indicated that L. salicaria is facultatively mycorrhizal and capable of forming vesicular-arbuscular associations with six Glomus species, but not with Gigaspora margarita. Overall, hyphal and arbuscular colonization levels were significantly higher in the wet treatments than in the dry treatments (P<0.0001). However, taken individually, significant increases in arbuscular colonization (P<0.05) were found only in L. salicaria colonized with Glomus clarum, G. aggregatum, and G. versiforme and exposed to the wet treatments compared with the dry treatments, while significant increases in hyphal colonization were found in L. salicaria colonized with G. clarum, and G. versiforme exposed to the wet treatments. There was no overall effect of water availability on levels of vesicular colonization or differences in vesicular colonization levels within species under dry or wet conditions. In contrast, field studies along an existing water gradient revealed that hyphal and arbuscular colonization levels were significantly higher (P<0.05) in the dry and intermediate regions of the gradient than in the wet regions. Vesicular colonization was not significantly affected by the gradient. Total stem height was significantly affected by water availability, plot location and an interaction of the two (P<0.05), and was generally higher in the intermediate and wet plots. Accepted: 20 September 1995     

The implications of accepting untestedhypotheses: a review of the effectsof purple loosestrife (Lythrum salicaria)in North America

The acceptance of poorly tested hypotheses has adverse scientific consequences, and may have adverse ecological and social consequences. The hypothesis that purple loosestrife (Lythrum salicaria) has deleterious effects on North American wetlands is an example. We traced the history of purple loosestrife and its control in North America and found little scientific evidence consistent with the hypothesis that purple loosestrife has deleterious effects. The most commonly cited study of the effects of purple loosestrife on native flora and fauna produced inconclusive results. The general acceptance of this hypothesis, however, has resulted in the introduction of nonindigenous insects for biological control. Efforts to control purple loosestrife may be misplayed and may have long-term ecological consequences if loosestrife does not have the impact it is believed to have. The acceptance of this hypothesis using scientific justifications may affect future scientific credibil ity. Careful evaluation of the precautionary principle is necessary when considering the control of nonindigenous organisms.     

Impact and management of purple loosestrife (Lythrum salicaria) in North America

The invasion of non-indigenous plants is considered a primary threat to integrity and function of ecosystems. However, there is little quantitative or experimental evidence for ecosystem impacts of invasive species. Justifications for control are often based on potential, but not presently realized, recognized or quantified, negative impacts. Should lack of scientific certainty about impacts of non-indigenous species result in postponing measures to prevent degradation? Recently, management of purple loosestrife (Lythrum salicaria), has been criticized for (1) lack of evidence demonstrating negative impacts of L. salicaria, and (2) management using biocontrol for lack of evidence documenting the failure of conventional control methods. Although little quantitative evidence on negative impacts on native wetland biota and wetland function was available at the onset of the control program in 1985, recent work has demonstrated that the invasion of purple loosestrife into North American freshwater wetlands alters decomposition rates and nutrient cycling, leads to reductions in wetland plant diversity, reduces pollination and seed output of the native Lythrum alatum, and reduces habitat suitability for specialized wetland bird species such as black terns, least bitterns, pied-billed grebes, and marsh wrens. Conventional methods (physical, mechanical or chemical), have continuously failed to curb the spread of purple loosestrife or to provide satisfactory control. Although a number of generalist insect and bird species utilize purple loosestrife, wetland habitat specialists are excluded by encroachment of L. salicaria. We conclude that (1) negative ecosystem impacts of purple loosestrife in North America justify control of the species and that (2) detrimental effects of purple loosestrife on wetland systems and biota and the potential benefits of control outweigh potential risks associated with the introduction of biocontrol agents. Long-term experiments and monitoring programs that are in place will evaluate the impact of these insects on purple loosestrife, on wetland plant succession and other wetland biota.     

Re-establishment of clinal variation in flowering time among introduced populations of purple loosestrife (Lythrum salicaria, Lythraceae)

Range expansion during biological invasion requires that invaders adapt to geographical variation in climate, which should yield latitudinal clines in reproductive phenology. We investigated geographic variation in life history among 25 introduced populations of Lythrum salicaria, a widespread European invader of North American wetlands. We detected a strong latitudinal cline in initiation of flowering and size at flowering, which paralleled that reported among native populations. Plants from higher latitudes flowered earlier and at a smaller size than those from lower latitudes, even when raised in a uniform glasshouse. Early flowering was associated with greatly reduced reproductive output, but this was not associated with latitudinal variation in abundance, and probably did not result from a genetic correlation between time to and size at flowering. As introduction to North America c. 200 years ago, L. salicaria has re-established latitudinal clines in life history, probably as an evolutionary response to climatic selection.     

DNA ploidy-level variation in native and invasive populations of Lythrum salicaria at a large geographical scale

Aim  This study aimed to document precisely the patterns of DNA ploidy variation in the native and secondary ranges of Lythrum salicaria distribution. The hypothesis that species invasiveness had been induced by a switch in ploidy level was addressed.
Location  Europe, Middle East, North America.
Methods  DNA ploidy levels of 1884 progenies of 578+ plants collected at 124 localities were determined by DAPI flow cytometry.
Results  Large cytotype variation (2 x , 3 x , 4 x and 6 x ) was found across the native area of distribution (64 populations covering 12 European and two Middle Eastern countries). DNA hexaploids were detected for the first time, and rare DNA triploids were reliably confirmed. DNA tetraploids largely prevailed across the native range studied, while DNA diploids and DNA hexaploids were recorded only in Israel and Turkey, respectively. DNA triploid progenies occurred in one population from Hungary (together with DNA tetraploids). Sympatric growth of DNA tetraploids and DNA hexaploids was repeatedly encountered in Turkey. In contrast, cytotype uniformity was a typical feature of the invasive North American plants. Sixty populations, covering 13 states of the USA and provinces of Canada, were characterized by the presence of only DNA tetraploids.
Main conclusions  Several L. salicaria cytotypes (2 x , 3 x , 4 x , 6 x ) occur in the native range of distribution, with much variation concentrated in the Middle Eastern countries, whereas only DNA tetraploids appeared to occur in North America. Our data show that the invasive spread of North American populations was not triggered by differences in ploidy level. Alternative explanations should be sought.     

Comparison of quantitative and molecular variation in agroforestry populations of the shea tree (Vitellaria paradoxa C.F. Gaertn) in Mali

In this study we investigated the within- and between-population genetic variation using microsatellite markers and quantitative traits of the shea tree, Vitellaria paradoxa, an important agroforestry tree species of the Sudano–Sahelian region in Africa. Eleven populations were sampled across Mali and in northern Côte d’Ivoire. Leaf size and form and growth traits were measured in a progeny test at the nursery stage. Eight microsatellites were used to assess neutral genetic variation. Low levels of heterozygosity were recorded (1.6–3.0 alleles/locus; H_E = 0.25–0.42) and the fixation index (F_IS = −0.227–0.186) was not significantly different from zero suggesting that Hardy–Weinberg equilibrium is encountered in all populations sampled. Quantitative traits exhibited a strong genetic variation between populations and between families within populations. The degree of population differentiation of the quantitative traits (Q_ST = 0.055–0.283, Q_STmean = 0.189) strongly exceeds that in eight microsatellite loci (F_ST = −0.011–0.142, F_STmean = 0.047). Global and pairwise F_ST values were very low and not significantly different from zero suggesting agroforestry practices are amplifying gene flow (Nm = 5.07). The population means for quantitative traits and the rainfall variable were not correlated, showing variation was not linked with this climatic cline. It is suggested that this marked differentiation for quantitative traits, independent of environmental clines and despite a high gene flow, is a result of local adaptation and human selection of shea trees. This process has induced high linkage disequilibrium between underlying loci of polygenic characters.     

Habitat and Population Effects on the Germination and Early Survival of the Invasive Weed, Lythrum salicaria L. (purple loosestrife)

In this study, we examined how environmental factors and differences among populations of Lythrum salicaria L. (Lythraceae; purple loosestrife) influenced the establishment of this species into both its preferred wetland habitat and secondary upland habitat. Seeds and seedlings from five parents from each of the three populations were planted in each wetland and upland of two sites in both disturbed and undisturbed plots. More seeds germinated in wetland than in upland sites (31% as compared to 11%) and, although a disturbance resulted in greater germination (23% as compared to 17% in undisturbed plots), there was no interaction with habitats. The results of a simultaneous greenhouse germination study in which seeds were planted under saturated and drained conditions suggest that the higher germination observed in wetland sites was due to the higher moisture present at such sites (79% vs. 45% in saturated and drained conditions, respectively). Disturbance enhanced both germination and growth of L. salicaria and this was especially so for seedlings. Dry weights of seedlings from disturbed plots were five times greater than those from undisturbed plots ( =9.2 vs. 1.8g in disturbed and undisturbed conditions, respectively). In addition to environmental factors, population differences are likely to play an important role in the spread of L. salicaria as we found differences between the populations in both life stages examined. One of the populations germinated equally well in both moisture treatments. In our seedling establishment experiment, one of the populations produced both the smallest plants and the most and earliest flowers, suggesting superior reproduction.     

Comparison of life history traits between invasive and native populations of purple loosestrife (Lythrum salicaria) using nonlinear mixed effects model

We compared growth patterns of invasive and native populations of purple loosestrife (Lythrum salicaria) while varying water and nutrient levels. We examined three life-history traits (height, number of branches, and the size of largest leaf) during the growth period adopting a nonlinear mixed effects model. Invasive populations were found to be slower in shoot elongation but grew to be taller than native populations. Invasive populations produced more branches than natives only in the high water, high nutrient treatment. Invasive populations had a similar increase in the size of the largest leaf compared to natives, but ultimately produced a greater size of largest leaf than natives. Invasive populations were found to display a greater vegetative expansion, but this was not strongly affected by our treatments.     

Comparison of life history traits between invasive and native populations of purple loosestrife (Lythrum salicaria) using nonlinear mixed effects model

We compared growth patterns of invasive and native populations of purple loosestrife (Lythrum salicaria) while varying water and nutrient levels. We examined three life-history traits (height, number of branches, and the size of largest leaf) during the growth period adopting a nonlinear mixed effects model. Invasive populations were found to be slower in shoot elongation but grew to be taller than native populations. Invasive populations produced more branches than natives only in the high water, high nutrient treatment. Invasive populations had a similar increase in the size of the largest leaf compared to natives, but ultimately produced a greater size of largest leaf than natives. Invasive populations were found to display a greater vegetative expansion, but this was not strongly affected by our treatments.     

Predicting the pathway to wind pollination: heritabilities and genetic correlations of inflorescence traits associated with wind pollination in Schiedea salicaria (Caryophyllaceae)

The transition from biotic to abiotic pollination was investigated using Schiedea, a genus exhibiting a remarkable diversity of inflorescence architecture associated with pollination biology. Heritabilities and genetic correlations of inflorescence traits were estimated in gynodioecious Schiedea salicaria (Caryophyllaceae), a species that has likely undergone a recent transition to wind-pollination. Using a partial diallel crossing design, significant narrow-sense heritabilities were detected for inflorescence condensation (h2 = 0.56 to 0.68 in the two sexes) and other traits related to the extent of wind pollination in Schiedea species. Heritabilities were generally higher in hermaphrodites than in females. Strong genetic correlations may constrain the evolution of some inflorescence traits that facilitate wind pollination, such as simultaneous shortening of inflorescence length and elongation of the subtending internode. The presence of significant narrow-sense heritabilities for traits associated with wind pollination suggests, however, that selection for more effective wind pollination in the windy, pollinator-limited environments where S. salicaria grows could lead to the evolution of the highly condensed inflorescences characteristic of other wind-pollinated species of Schiedea.     

Comparison of genetic diversity at microsatellite loci and quantitative traits in hatchery populations of Japanese flounder Paralichthys olivaceus

Relationships of genetic diversity at microsatellite loci and quantitative traits were examined in hatchery-produced populations of Japanese flounder using a relatively straightforward experiment. Five hatchery populations produced by wild-caught and domesticated broodstocks were used to examine the effects of different levels (one to three generations) of domestication on the genetic characteristics of hatchery populations. Allelic richness at seven microsatellite loci in all hatchery populations was lower than that in a wild population. Genetic variation measured by allelic richness and heterozygosity tended to decrease with an increase in generations of domestication. In addition, the degree of genetic differentiation from a wild population increased with an increase in generations of domestication. Significant differences in three morphometric traits (dorsal and anal fin ray counts and vertebral counts) and three physiological traits (high temperature, salinity and formalin tolerance) were observed among the hatchery populations. The degree of phenotypic difference among populations was larger in morphometric traits than in physiological traits. The divergence pattern of some quantitative traits was similar to that observed at microsatellite loci, suggesting that domestication causes the decrease of genetic variation and the increase of genetic differentiation for some quantitative traits concomitantly with those for microsatellite loci. Significant positive correlation was observed between F _ST and the degree of phenotypic difference in the three morphometric traits and formalin tolerance, indicating that genetic variation at microsatellite loci predicts the degree of phenotypic divergence in some quantitative traits.     

Latitudinal divergence of common frog (Rana temporaria) life history traits by natural selection: evidence from a comparison of molecular and quantitative genetic data

The relative roles of natural selection and direct environmental induction, as well as of natural selection and genetic drift, in creating clinal latitudinal variation in quantitative traits have seldom been assessed in vertebrates. To address these issues, we compared molecular and quantitative genetic differentiation between six common frog (Rana temporaria) populations along an approximately 1600 km long latitudinal gradient across Scandinavia. The degree of population differentiation (QST approximately 0.81) in three heritable quantitative traits (age and size at metamorphosis, growth rate) exceeded that in eight (neutral) microsatellite loci (FST = 0.24). Isolation by distance was clear for both neutral markers and quantitative traits, but considerably stronger for one of the three quantitative traits than for neutral markers. QST estimates obtained using animals subjected to different rearing conditions (temperature and food treatments) revealed some environmental dependency in patterns of population divergence in quantitative traits, but in general, these effects were weak in comparison to overall patterns. Pairwise comparisons of FST and QST estimates across populations and treatments revealed that the degree of quantitative trait differentiation was not generally predictable from knowledge of that in molecular markers. In fact, both positive and negative correlations were observed depending on conditions where the quantitative genetic variability had been measured. All in all, the results suggest a very high degree of genetic subdivision both in neutral marker genes and genes coding quantitative traits across a relatively recently (< 9000 years) colonized environmental gradient. In particular, they give evidence for natural selection being the primary agent behind the observed latitudinal differentiation in quantitative traits.     

Genetic diversity and population structure of invasive and native populations of Erigeron canadensis L.

小蓬草入侵地和原产地种群的遗传多样性和种群结构 外来入侵植物对全球生物多样性造成了危害。小蓬草(Erigeron canadensis L.)是危害最为严重的外来农业杂草之一,代表了洲际入侵的典型例子。本研究利用10个多态性SSR位点,分别对采自中国江苏和浙江省的入侵地和采自美国阿拉巴马州的原产地各5个种群、共计312个植株的基因型进行了遗传多样性和遗传结构分析。结果表明,江苏省和浙江省的入侵种群显示出与阿拉巴马州原产地种群相似的遗传多样性,表明入侵期间没有严重的遗传瓶颈。利用STRUCTURE对种群结构的分析结果显示,种群之间分化较低,在原产地和入侵范围内均只仅检测到两个基因群。在入侵种群中观察到的遗传多样性较高,表明在入侵初期可能存在多次引入或引入了遗传背景不同的繁殖体。上述研究为阐明小蓬草这一全球有害杂草在中国东部的入侵动态提供了新的证据。在防除实践中,应注意防范小蓬草入侵种群和本地种群之间的种子基因流传播,阻止除草剂抗性植株的引入和扩散。     

Genetic variation of Eryngium campestre L. (Apiaceae) in Central Europe

In Germany, Eryngium campestre is restricted to dry habitats along the rivers Rhine and Elbe and to a few areas in Central Germany. This distribution pattern is usually regarded as a typical pattern of postglacial immigration. In the present study, we investigated whether these two geographically distinct distribution areas are genetically differentiated and whether conclusions can be drawn regarding colonization history. To analyse the phylogeographic structure of E. campestre in Central Europe, 278 individuals from 29 populations within Germany and from further reference populations within Europe were analysed. We applied amplified fragment length polymorphisms to examine their genetic relatedness. Our analyses revealed three groups: a Mediterranean group additionally including two Rhine populations; a Rhine–Main group which further includes the westernmost population from the central German dry area; and one group which includes all eastern populations. Our results show that the two geographically distinct areas are genetically differentiated. As genetic diversity within the Elbe populations is very low, we conclude that this area, which was strongly affected through the late glacial maximum, was colonized relatively recently. High genetic diversity in the Rhine populations indicates a contact zone where lineages of different origin met. This would imply that today's patterns of genetic variation were caused through glacial range contractions and expansions. The present study is one of the first studies that deal with the postglacial distribution pattern of a dry grassland plant species in Central Europe and the results suggest that a survival of E. campestre at least during the Dryas cold stage might be possible.     

Genetic diversity of Ranunculus acris L. (Ranunculaceae) populations in relation to species diversity and habitat type in grassland communities

Correlates between genetic diversity at intra- and interpopulation levels and the species diversity in plant communities are rarely investigated. Such correlates may give insights into the effect of local selective forces across different communities on the genetic diversity of local plant populations. This study has employed amplified fragment length polymorphism to assess the genetic diversity within and between 10 populations of Ranunculus acris in relation to the species diversity (richness and evenness) of grassland communities of two different habitat types, 'seminatural' and 'agriculturally improved', located in central Germany. Within-population genetic diversity estimated by Nei's unbiased gene diversity (HE) was high (0.258-0.334), and was not correlated with species richness (Pearson's r = -0.17; P = 0.64) or species evenness (Pearson's r = 0.15; P = 0.68) of the plant communities. However, the genetic differentiation between R. acris populations was significantly correlated with the difference in species evenness (Mantel's r = 0.62, P = 0.02), but not with difference in species richness of plant communities (r = -0.17, P = 0.22). Moreover, we also found that populations of R. acris from the 'seminatural' habitat were genetically different (amova, P < 0.05) from those in 'agriculturally improved' habitats, suggesting that gene flow between these habitat types is limited. The results reported in this study may indicate that habitat characteristics influence the genetic diversity of plant species.     

Allozyme differentiation and genetic structure of the Lady's slipper (Cypripedium calceolus) island populations in north-east Poland

The population genetic structure in the rare and endangered perennial plant, Cypripedium calceolus , from north-east Poland was investigated. A total of 11 loci were analysed, of which five were polymorphic for the species and in every population. The 11 loci resolved gave a total of 19 alleles with the mean number of 1.73 alleles per locus. The proportion of polymorphic loci (P) was the same for the species and in every population, 45.5%. The average observed and expected heterozygosities for the total Lady's slipper data set were 0.156 and 0.184, respectively. The average expected heterozygosity for the populations under study ranged from 0.176 to 0.188 and did not differ significantly among populations. Genetic diversity within C. calceolus populations from the Biebrza Valley is relatively high compared with rare taxa and taxa with similar life histories. The genetic diversity among populations of C. calceolus studied ( F _ST = 0.016) is much smaller than the genetic diversity within populations. In the species studied, there was no significant correlation between genetic and geographical distances ( r = −0.73, Mantel test). This may indicate the relatively recent origin of the populations studied, or a high level of gene flow among populations. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society , 2002, 138 , 433–440.     

A preliminary study of genetic variation in populations of Monstera adansonii var. klotzschiana (Araceae) from North-East Brazil, estimated with AFLP molecular markers

BACKGROUND AND AIMS: This study sought genetic evidence of long-term isolation in populations of Monstera adansonii var. klotzschiana (Araceae), a herbaceous, probably outbreeding, humid forest hemi-epiphyte, in the brejo forests of Ceará (north-east Brazil), and clarification of their relationships with populations in Amazonia and the Atlantic forest of Brazil. METHODS: Within-population genetic diversity and between-population dissimilarity were estimated using AFLP molecular markers in 75 individuals from eight populations located in Ceará, the Brazilian Atlantic Forest and Amazonia. KEY RESULTS: The populations showed a clinal pattern of weak genetic differentiation over a large geographical region (F(ST) = 0.1896). A strong correlation between genetic and geographical distance (Mantel test: r = 0.6903, P = 0.002) suggests a historical pattern of isolation by distance. Genetic structure analysis revealed at least two distinct gene pools in the data. The two isolated Ceará populations are significantly different from each other (pairwise Phi(PT) = 0.137, P = 0.003) and as diverse (Nei's gene diversity, average H(e) = 0.1832, 0.1706) as those in the Atlantic and Amazon forest regions. The population in southern Brazil is less diverse (Nei's gene diversity, average H(e) = 0.127) than the rest. The Ceará populations are related to those of the Atlantic forest rather than those from Amazonia (AMOVA, among-groups variation = 11.95 %, P = 0.037). CONCLUSIONS: The gene pools detected within an overall pattern of clinal variation suggest distinct episodes of gene flow, possibly correlated with past humid forest expansions. The Ceará populations show no evidence of erosion of genetic diversity, although this was expected because of their isolation. Their genetic differentiation and relatively high diversity reinforce the importance of conserving the endangered brejo forests.     

Assessment of genetic variation in Sicilian Helichrysum (Asteraceae) and implication to germplasm conservation

Abstract

Some taxa of Sicilian Helichrysum related to sect. Stoeachadina have an uncertain systematic position; moreover, they are rare and endangered. In order to preserve these taxa in a genebank, a strategy to keep their genetic variation as high as possible is required. The high informative content of AFLP markers was used to assess genetic variations within and between populations and their relationships. The results show that all populations are genetically similar, even though there are two distinct groups: the first is the population referred to H. pendulum, and the second is represented by other populations belonging to several different specific and intraspecific taxa. The H. pendulum population is homogeneous, and characterised by the lowest genetic variation among all the populations considered. The second group shows a greater variation as evidenced by the presence of three subgroups: (i) populations referred to H. panormitanum var. panormitanum and H. panormitanum var. stramineum, (ii) populations referred to H. errerae var. errerae and H. errerae var. messerii, (iii) a population referred to H. hyblaeum, which, despite morphological and chorological differences, is similar to the other populations of the second group from a genetic stand point. Each population of the above-mentioned taxa has local fragment markers whose frequency is useful to determine how many plants should be sampled in order to collect the seeds necessary to preserve the population's genetic diversity in a genebank.