Carduus Species Research Articles

Plant phylogeny determines host selection and acceptance of the oligophagous leaf beetle Cassida rubiginosa.

Predicting the host range of biocontrol agents is important for the safe and effective implementation of biocontrol of weeds. In this study, we examined the phylogenetic pattern of host selection and acceptance by the biocontrol beetle, Cassida rubiginosa. The beetle was released in New Zealand for control of Cirsium arvense, its primary host plant, but has potential to attack many Cardueae (thistles and knapweeds) species. We conducted a series of no-choice and choice experiments and modelled the responses of Cassida rubiginosa in relation to phylogenetic distance from Cirsium arvense. The olfactory recognition (single odour) and preference (two odours) of the beetle showed a significant phylogenetic relationship. These relationships showed a high degree of correlation with 66.9% of the variation in olfactory recognition and 82.8% of the variation in olfactory preference explained by phylogeny. Where the beetle could contact plants, under no-choice conditions there was no phylogenetic pattern to host plant acceptance. However, under choice conditions, phylogenetic distance was a strong predictor of feeding and oviposition preference. These relationships showed a high degree of correlation, with 63.4% of the variation in feeding preference, and 89.0% of the variation in oviposition preference, explained by phylogeny. As far as we are aware, this is the first demonstration of an herbivorous insect that exhibits a phylogenetic pattern to olfactory host plant selection. Host plant utilisation by Cassida rubiginosa in New Zealand will be mostly restricted to Cirsium and Carduus species, with minimal potential for impact on other Cardueae weeds. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Phenolic Composition of Inflorescences of Carduus nutans L.

Carduus nutans L. (Compositae) has been extensively used for medicinal purposes. As other representatives of the genus it is implemented in the treatment of liver disorders and used as diuretic and digestive agent. Previous studies have determined the predominant classes of secondary metabolites in Carduus species. Among the major representatives of their extracts flavonoids, phenolic acids, coumarins, sterols and terpenes were identified. The antiradical capacity of three extracts assessed in the DPPH test revealed the highest radical scavenging properties of methanol extract (the EC50 618±10.03 μg/mL) and based on these results it was selected for phenolic content determination. (TPC=61.49 mg/g). To understand better the induced pharmacological effects of the plant the aim of the study was to determine the composition of the methanol extract from the inflorescences of C. nutans and to study their phenolic composition. In order to determine the composition in a more efficient way, the crude extract was fractionated and subjected to hydrolyses. As a result more than twenty phenolic acids and flavonoids were identified in the extract and fractions by HPLC-DAD and/or HPLC-ESI-TOF-MS. The total extract was later subjected to fractionation by centrifugal partition chromatography using the Arizona system composed of hexane/ethyl acetate/methanol/water (0.7 : 4 : 0.8 : 4 v/v/v/v) to produce fractions enriched in flavonoids that are of high pharmacological significance.

Comparative analysis and implications of the chloroplast genomes of three thistles (Carduus L., Asteraceae).

BackgroundCarduus, commonly known as plumeless thistles, is a genus in the Asteraceae family that exhibits both medicinal value and invasive tendencies. However, the genomic data of Carduus (i.e., complete chloroplast genomes) have not been sequenced.MethodsWe sequenced and assembled the chloroplast genome (cpDNA) sequences of three Carduus species using the Illumina Miseq sequencing system and Geneious Prime. Phylogenetic relationships between Carduus and related taxa were reconstructed using Maximum Likelihood and Bayesian Inference analyses. In addition, we used a single nucleotide polymorphism (SNP) in the protein coding region of the matK gene to develop molecular markers to distinguish C. crispus from C. acanthoides and C. tenuiflorus.ResultsThe cpDNA sequences of C. crispus, C. acanthoides, and C. tenuiflorus ranged from 152,342 bp to 152,617 bp in length. Comparative genomic analysis revealed high conservation in terms of gene content (including 80 protein-coding, 30 tRNA, and four rRNA genes) and gene order within the three focal species and members of subfamily Carduoideae. Despite their high similarity, the three species differed with respect to the number and content of repeats in the chloroplast genome. Additionally, eight hotspot regions, including psbI-trnS_GCU, trnE_UUC-rpoB, trnR_UCU-trnG_UCC, psbC-trnS_UGA, trnT_UGU-trnL_UAA, psbT-psbN, petD-rpoA, and rpl16-rps3, were identified in the study species. Phylogenetic analyses inferred from 78 protein-coding and non-coding regions indicated that Carduus is polyphyletic, suggesting the need for additional studies to reconstruct relationships between thistles and related taxa. Based on a SNP in matK, we successfully developed a molecular marker and protocol for distinguishing C. crispus from the other two focal species. Our study provides preliminary chloroplast genome data for further studies on plastid genome evolution, phylogeny, and development of species-level markers in Carduus.

CARDUUS CINEREUS (ASTERACEAE) – NEW TO NORTH AMERICA

Carduus cinereus M.Bieb. populations have been discovered in the Hells Canyon Wilderness of northeastern Oregon and western Idaho. These plants were initially identified as C. pycnocephalus L. They are distinguished from that species by loosely clustered, usually pedunculate, heads and by scarious-margined phyllaries. These plants are genetically distant from other North American Carduus species (<94% similarity) based on DNA sequence comparisons of the internal transcribed spacers between the 18S and 26S nuclear rDNA regions. Carduus cinereus is new to North America. A revised key to the species of Carduus in North America is presented.

Micro-morphology and molecular investigations in some Carduus species in Iran

The genus Carduus L. comprised about 90 species, some of which are medicinally important and have high content of flavonoids, and phenolic acids. There are about nine Carduus species growing in Iran, out of which one species is endemic. Biosystematic investigation of the genus has been confined to morphological and palynological studies only and we do not have information on molecular study, species relationships and genetic structure of Carduus taxa in the country. We therefore, carried out multiple data set analyses of these species for the first time by using micro-morphological and molecular characteristics and provide data on species diversification and their affinities for the first time. The results showed that micro-morphological data can differentiate Carduus species, while the species relationship obtained by different approaches may disagree in some points. The results suggest that complexity observed in the taxonomy of the genus Carduus may be due to historical introgression events occurred between nuclear and chloroplast genomes during species diversification.

Review of the Tephritis hyoscyami–conura Group of Species (Diptera: Tephritidae) with Description of a New Species

The fruit flies of the genus Tephritis associated with the host plants of closely related asteraceous plant species of Cirsium and Carduus (Asteraceae: Cardueae: Carduinae) are revised. In particular, six species of this group known to occur in the western part of the Palaearctic Region are discussed in this article. Three of them, Tephritis conura (Loew 1844), T. hendelianaHering 1944, and T. hyoscyami (Linnaeus 1758) are widespread, predominantly European species. Two other ones, T. cardualisHardy 1974 from Pakistan and T. atokopteraAgarwal & Kapoor 1988 from India, were previously known mostly from the original descriptions and are redescribed here. Finally, T. anthraxsp. nov. from Caucasian and Transcaucasia mountains is described. Species are keyed and illustrated. New distribution records and host plants are reported.

Genetic diversity of Bulgarian representatives of genus Carduus L. (Asteraceae) as revealed by variability in sequences of internal transcribed spacers region

ABSTRACTThe biodiversity of genus Carduus in Bulgaria is grossly under-studied with modern methods, which leads to unclear status of species and hampers the assessment of their habitats and conservation status. In this study, we used the variability of internal transcribed spacers (ITS) to investigate the biodiversity of Carduus species collected from different floristic regions of Bulgaria. Thirty-three samples were processed. Among the studied species, C. acanthoides exhibited the highest ITS variability (eight single nucleotide polymorphisms were found). High ITS variability was also found in C. crispus and C. hamulosus, demonstrating that some of the local Carduus species possesses unique genetic diversity, which can serve as source for future divergence of new forms and subspecies. For each species, unique nucleotides suitable as molecular taxonomy markers were identified. However, C. nutans and C. thoermeri displayed completely identical ITS sequences, which is in agreement with all ITS sequences of these species collected elsewhere in the world and deposited in the NCBI database. After careful analyses of both molecular and morphological data, we propose to restore C. nutans and C. thoermeri as one species with two subspecies. Namely, Carduus nutans subsp. nutans and Carduus nutans subsp. thoermeri. We recommend diameter of capitulum, length of peduncle, width of peduncle and width of bract as diagnostic features of taxonomic significance for distinguishing the two subspecies.

Characterization of four wild edible Carduus species from the Mediterranean region via phytochemical and biomolecular analyses

Carduus species (Compositae) are widely distributed in the Mediterranean area, and traditionally used for both food and medicinal purposes.The hydroalcoholic extracts of four wild edible Carduus species collected in Sardinia (Carduus argyroa Biv., Carduus nutans subsp. macrocephalus (Desf.) Nyman, Carduus pycnocephalus L., Carduus cephalanthus Viv.) were analyzed and characterized by HPLC-PDA-MS/MS and PCR-RFLP of the nrDNA internal transcribed spacer (ITS).Flavonoids and caffeoylquinic acid derivatives were the predominant classes of secondary metabolites characterizing the extracts. The ITS region was sequenced in parallel, and a PCR-RFLP method was applied with three selective restriction enzymes. Statistical analyses, on both chemical and biomolecular results, revealed that individuals clustered according to their taxonomic classification.The combination of the two techniques discriminates the four species within the genus, giving further information on these little-investigated plants, traditionally used in the Mediterranean area and in Sardinia.

Caracterización y fenología de especies de interés apícola en el departamento Diamante (Entre Ríos, Argentina)

Con el objeto de evaluar los recursos apícolas de la región suroeste de la provincia de Entre Ríos en cuanto a riqueza y abundancia, disponibilidad temporal y espacial de los mismos, se relevó lavegetación en el área de influencia de 3 apiarios. Contar con esta información permitirá favorecer la planificación de la actividad apícola y comparar con los recursos explotados por Apis mellifera. Durantelas temporadas apícolas 1999-2001 se registró la floración de 299 Angiospermae y determinó la cobertura en diferentes ambientes. Las familias apícolas con mayor diversidad de especies fueron Asteraceae y Fabaceae. El periodo de floración se extendió durante todo el año, con un máximo entre mediados de octubre a fin de febrero. Las familias botánicas, más relevantes en la oferta de floración fueron Asteraceae, Fabaceae, Apiaceae y Brassicaceae. Las especies arbóreas hacen su aporte principalmente al principio de la temporada, siendo ampliamente superadas desde septiembre en adelante por las herbáceas. El recurso apícola en el sector de tierra firme, se halla representado principalmente por hierbas exóticas (e.g. Glycine max, Melilotus albus, Medicago sativa, Lotus corniculatus, Brassica campestris, especies de Ammi y Carduus) y en el sector costero y de islas por especies nativas acuáticas y palustres, tanto herbáceas (e.g. Sagittaria montevidensis, especies de Polygonum y Eichhornia) como arbóreas (e.g. Salix humboldtiana y Tessaria integrifolia). Las especies del humedal permiten extender el periodo apícola hacia principios de otoño.

Karyological studies of eightCarduusL. (Asteraceae, Cardueae) taxa from Turkey

The somatic chromosome numbers and detailed morphometric properties of 18 specimens belonging to eight taxa (six species) of genus Carduus L. distributed in Turkey were examined. The somatic chromo...

Phenolic Profile and In vitro Antioxidant Activity of Endemic Bulgarian Carduus Species.

Background:Plant species from genus Carduus are widely distributed in the world and represented in Bulgaria by 14 species. Previous investigations on this genus demonstrated a strong antioxidant potential of extract from some Bulgarian Carduus species.Objective:The present study investigates the phenolic profile and the antioxidant potential of different extracts obtained from four endemic Compositae herbs, growing wild in Bulgaria: Carduus armatus Boiss and Heldr., Carduus candicans Waldst. et Kit ssp. globifer (Velen.) Kazmi., Carduus rhodopaeus Velen. and Carduus thracicus (Velen.) Hayek.Materials and Methods:Antioxidant capacity of the obtained extracts was estimated with 2,2-diphenyl-1-picrylhydrazyl, 2,2’-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid), and ferric reducing antioxidant power and copper reduction antioxidant assays. Phenolic profile was estimated by high performance liquid chromatography.Results:Eleven phenolic acids and eight flavonoids were quantified in the inflorescences. Sinapic (2760.72 ± 15.68 μg/g dry weight [dw]), chlorogenic (2564.50 ± 19.73 μg/g dw) and ferulic acids (1648.71 ± 19.57 μg/g dw), as well as luteolin (2345.45 ± 18.61 μg/g dw) and apigenin (1332.75 ± 12.05 μg/g dw) were found to be the predominant compounds. The above contents are the highest values found in C. candicans ssp. globifer. The highest established antioxidant activity (AOA) was in favor of the ethanolic extracts, and the extract of C. rhodopaeus affirmed with the highest AOA among the investigated plant species.Conclusion:All identified phenolic compounds were reported for the 1st time in the studied endemic Carduus species, as well as their antioxidant capacities. The present study revealed that these plant species could be used as sources of antioxidants with potential medicinal properties.SUMMARY Phenolic acids and flavonoid profiles of four endemic compositae herbs, growing wild in Bulgaria: Carduus armatus, Carduus candicans ssp. globifer, Carduus rhodopaeus and Carduus thracicus, were quantified for the first time by high performance liquid chromatography (HPLC). Eleven phenolic acids and eight flavonoids were determined in the inflorescences. Sinapic, chlorogenic and ferulic acids, as well as luteolin and apigenin were found to be the predominant compounds. The highest values of established phenolic compounds were found in C. candicans ssp. globifer. The studied plant extracts of Carduus species possessed antioxidant activity in favor of C. rhodopaeus and results confirmed 70 % ethanol as more appropriate solvent. The present study revealed that these plant species could be used as sources of antioxidants with potential medicinal properties.

Cypselar morphology of Carduus L. (Asteraceae) taxa in Turkey and its taxonomic implications

Cypselar morphology of 24 taxa including 16 species and eight subspecies of the 29 Turkish Carduus L. (Asteraceae) taxa (belonging to 17 species) were examined by stereomicroscope and scanning electron microscope. In this study, nine qualitative characters (cypselar shape, symmetry, kurtosis, surface ornamentation and different features of cypselar surface cells) and five quantitative characters (cypselar length and width, umbo length and width, ring diameter) were examined. Macromorphological studies revealed oblanceolate, narrowly obovate, narrowly oblong to oblong cypselar shapes with striate or furrowed surface. Based on scanning electron microscopic investigation of cypselar surface, the studied taxa were divided into five main types: scalariform, scalariform-ribbed, scrobiculate-ribbed, scrobiculate and scrobiculate-foveolate. An identification key of studied species based on cypselar morphology has been provided. The results indicate that cypselar features can be used as diagnostic taxonomic characters in examined Carduus species.

Establishment, dispersal, and prevalence of Rhinocyllus conicus (Coleoptera: Curculionidae), a biological control agent of thistles, Carduus species (Asteraceae), in Argentina, with experimental information on its damage

Use of the weevil, Rhinocyllus conicus Froelich, for classical biological control of Carduus species in Argentina has not been controversial, as it has been in Canada and the United States, because there are no native thistle species in the South American release areas. In this study, 30years after its first field release in Argentina, the Pampas region was surveyed to confirm the establishment of R. conicus, covering the original release sites and most of the overall area of distribution of its host thistles, Carduus species. Sites (n=121) were systematically selected and natural populations of thistles were examined to confirm the presence of the weevil. Twenty four sites with R. conicus were selected to record the weevil’s prevalence on Carduus thoermeri Weinman and Carduus acanthoides L. Additional opportunistic surveys were conducted in other regions of Argentina and Uruguay, more distant from the original release sites. Rhinocyllus conicus was found at 81% of the original release sites and at 69% of the total sites surveyed, an area of approximately 370.000km2. On average, 92% of the examined heads had damage in areas where the weevil was present, showing its high prevalence. A pilot study showed that the oviposition period of the weevils lasted 119days and seed production of C. acanthoides was reduced by 15.5%. These results encourage the implementation of an integrated management of thistles in Argentina, and maybe in other parts of South America.

Influence of Microsite Disturbance on the Establishment of Two Congeneric Invasive Thistles

The successful establishment of invasive species has been shown to depend on aspects of the invaded community, such as gap characteristics. Biotic resistance may be particularly critical for stopping invaders at early life history stages, but new species can often invade following disturbances, which may create microsites with very different characteristics than are usually present. We examine the response of two invasive thistle species, Carduus nutans L. and C. acanthoides L., to three different microsite characteristics: disturbance type, size, and water availability. The two species initially responded differently to the type of disturbance: C. acanthoides had higher emergence and survival in plots with both above- and belowground disturbance, whereas C. nutans had better early performance in large microsites with above-ground disturbance only. Later in their life cycle, C. nutans performed better in plots that had been disturbed both above- and belowground, whereas C. acanthoides was largely unaffected by disturbance type. Increased emergence and survival, larger size and a higher proportion flowering were observed in larger gaps for both species throughout the life cycle. Watering had a negative impact on C. nutans emergence and fall survival and on C. acanthoides survival to the following summer. Overall, these results suggest that disturbance-generated microsite characteristics (disturbance type and size) may have large impacts on establishment of these two Carduus species, which in turn may persist well beyond the initial stages of growth. Studying invader responses to disturbance can help us to understand under what circumstances they are likely to establish and create persistent problems; avoiding or ameliorating such situations will have significant management benefits.

Antioxidant Activity of Some Carduus Species Growing in Bulgaria

Background: Species of genus Carduus are traditionally used in Bulgarian folk medicine as diuretic, cardiotonic and antihemorroidal remedies. C. candicans ssp. globifer and C. kerneri ssp. austro-orientalis are Balkan endemic, whereas C. acanthoides, C. nutans, C. thoermeri C. are invasive alien weeds in the Americas, Australia and New Zealand, and causes major economic losses. The aim of the present study was to screen some Carduus spesies growing in Bulgaria for radical scavenging and inhibitition of lipid peroxidation in order to discover new natural sources of antioxidants for further investigation. Methods: Antioxidant activity of Carduus species were investigated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2´-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) di-ammonium salt (ABTS) free radicals; ferric reducing antioxidant power (FRAP) assay and inhibition of lipid peroxidation in linoleic acid system by the ferric thiocyanate method (FTC). Butylated hydroxytoluene (BHT) and ascorbic acid were used as positive controls. In addition, the quantification of total water soluble polyphenols and flavanoids were determinate by Folin-Chiocalteu reagent and AlCl3, respectively. Results: The highest concentrations of total water soluble polyphenols and flavonoids were found in C. thoermeri (2.06 ± 0.03 g /100 g dw and 3.31 ± 0.12 g /100 g dw, respectively), followed by C. nutans (1.88 ± 0.01 g/100 g dw; 2.60 ± 0.09 g /100 g dw, respectively) and C. candicans ssp. globifer (1.85 ± 0.04 g/100 g dw). Conclusions: All tested extracts demonstrate significant antioxidant activity moreover C. thoermeri, C. nutans and C. candicans ssp. globifer were found to be the most potent and can be a good new source of natural antioxidants.

Vegetational history of the Late glacial–Holocene transition in the grasslands of eastern Argentina

Palynological records from eight sites located in the eastern plains of Argentina, from the humid Pampa in the east to the xerophytic woodland–dry Pampa ecotone in the west, allow a regional reconstruction of the vegetation of Late glacial–Holocene transition. Fossil pollen records were interpreted in terms of palaeoenvironmental information using the modern pollen–vegetation–climate relationship as an analogue. Although an exact analogue does not exist today, Late glacial vegetation consisted mostly of psammophytic steppe in large areas of the central and south-western Pampa grassland which, in the south west, is associated with a shrub steppe, suggesting subhumid–dry to semi-arid climatic conditions. The replacement of dry steppe by humid grassland and the rapid evolution of pond environments during the early Holocene (starting during the Late glacial–Holocene transition) suggests a shift towards subhumid to humid climate conditions. The Late glacial–Holocene transition is indicated in the pollen records by repeated abrupt changes in the proportions and concentrations of some taxa, such as Brassicaceae, Asteraceae and Carduus-type. In the modern vegetation they represent species of common occurrence in human-induced disturbance habitats, suggesting an environment that was subject to frequent natural disturbance such as rapid and repeated flooding episodes that inundated the depressions along the valley floodplains, caused by unusual rainfall events. Some species of Carduus may have been native and not introduced by the Europeans, suggesting that Late glacial vegetation of the Pampa grasslands may account for the abundance of ruderal species. Of special interest is the presence of Myrtaceae in some pollen assemblages between 11,000 and 9000 yr B.P. At present, Myrtaceae are not part of the natural vegetation in the Pampa grassland. Their presence in the fossil pollen records may be interpreted as local deposition instead of extra-regional origin. Myrtaceae formed part of the psammophytic steppe, and after Late glacial–Holocene transition they disappeared from the regional flora, perhaps due to the climatic change that occurred at the beginning of the Holocene. It is the most significant cause of extending the area of some Pampa grassland taxa, but it may have reduced the area for others. Of the Late glacial vegetation, at least Myrtaceae were probably not able to adapt to the new habitats and hence disappeared from the regional flora at the Pleistocene–Holocene transition. Although other plants may have disappeared as well, these cannot be identified because pollen from these plants cannot be differentiated morphologically. During the Late glacial–Holocene transition, communities with no modern counterparts probably formed and disappeared.

Endophagous insects and structural niches on plants: ecology and evolutionary consequences

Summary1. The endophagous weevil Lixus elongatus was studied on two Carduus species in order to look for the impact of a structural gradient in host plant stem diameter on the life cycle and the genetic structure of this species.2. Body size of L. elongatus females was correlated positively with their fecundity and the stem diameter at the location of oviposition.3. Emerging individuals showed a significantly positive relationship of body size with the stem diameter at their pupation and emergence site. Mating behaviour was positively size‐assortative.4. Allozyme analyses indicated a gradient of genetic differentiation along body size classes and a decreasing heterozygosity with decreasing body size.5. The results led to the conclusion that a structural gradient in plants can promote body size variability in an endophagous herbivore through phenotypic constraints of the host plant and the herbivore. As size‐assortative mating translates this variability into differential gene flow between individuals of different body size, this could provide the raw material for speciation processes. Within a single host plant patch, however, further processes are necessary to split the existing genetic gradient into separate gene pools.

Phenotypic Comparison ofPuccinia carduorumfromCarduus thoermeri, C. tenuiflorus,andC. pycnocephalus

Host range, urediniospore morphology, and isozyme banding patterns of field isolates of rust fungi from Carduus pycnocephalus, C. tenuiflorus, and C. thoermeri, collected in different geographic locations, were compared. Isolates from the three Carduus species are Puccinia carduorum, according to the isozyme data, supporting the view that P. carduorum is preferred to P. cardui-pycnocephali for isolates from C. pycnocephalus. Even though Rogers' Coefficient of Similarity supports the fact that the isolates are the same species, the isolates could be distinguished by isozyme banding patterns for aspartate aminotransferase and glucokinase (...)

Hybridization and Introgression in Carduus nutans and C. acanthoides Reexamined

The present paper provides a reexamination of an often cited example of hybridization and introgression in plants, that involving two introduced thistle species, Carduus nutans (2n = 16) and C. acanthoides (2n = 22), which occur sympatrically in Grey Co., Ontario, Canada. Evidence gathered from a range of characters (morphology, allozymes, flavonoids, molecular data, chromo- some numbers, and artificial hybridization and backcrossing experiments) revealed that both hy- bridization and backcrossing occur in this region. The two species were well separated morpho- logically, while the hybrid swarms exhibited the complete range of morphological variation evident for both species as well as intermediate types. There was a very close correlation with reduced fruit set and intermediacy in morphology. In contrast, a putative introgressed population, I1, exhibited a distinct shift towards C. acanthoides, with almost all individuals corresponding to an acanthoides or intermediate phenotype. Chromosome data from hybrid swarms and the introgressed population indicated a range of numbers from n = 8 to 11. Genetic identities based on allozyme frequencies was 0.68 between the two species and was 0.81 and 0.87 among the C. acanthoides and C. nutans populations, respectively. The three hybrid swarms showed equal similarity to both parental types, i.e., identity values of 0.82-0.83, while I1 was very similar to C. acanthoides. Allozyme data also confirmed the hybrid nature of the swarms with either additive or intermediate patterns. Flavonoid profiles were very similar in the two species. All individuals of C. acanthoides have the same four compounds, while populations of C. nutans were more variable and distinguished from C. acanthoides by the presence of up to three additional flavonoids. The hybrid swarms exhibited the complete range of flavonoid profiles, including characteristic acanthoides profiles, nutans profiles, and mixtures of the two. In artificial hybridization studies, C. nutans was the most frequent maternal parent, although both species served equally well as backcross parents. The F1 hybrids have 2n = 19 chromosomes and were almost completely sterile. Analyses based on 17 restriction enzymes, showed that the chloroplast genome and the transcribed region of the nuclear ribosomal genome of the two Carduus species are highly conserved; although some variation was detected in the ribosomal DNA spacer region. Although there was evidence of introgression in populations within the hybrid zone, patterns revealed by different characters were not always congruent. The results suggested that introgression may well be bidirectional. The Grey Co. region appears to represent a stable zone of hybridization in which the nature of the Carduus populations has changed little in the past 30 years.

Reproductive system and colonizing strategy of two species of Carduus (compositae).

Carduus pycnocephalus and C. tenuiflorus are two important weed species in mediterranean-type ecosystems. They were studied in their native habitat in southern France from April to December 1981.These species both produce two types of seed (achenes) in each capitulum. Those in the center are not dormant and are easily dispersed, while the outer ones can be dormant and have no apparent means of dispersal. Our observations on pollen transfer and self fertilization show that the dispersable, non dormant seeds have a low probability of inbreeding, while the potentially dormant, non dispersed seeds have a high probability of inbreeding. The significance of this dimorphism is discussed.