Comparison of chloroplast and nuclear phylogeny in the autogamous annualMicroseris douglasii (Asteraceae: Lactuceae)

Morphology suggests that the Californian annualMicroseris douglasii is a monophyletic sister group to the other three diploid annuals ofMicroseris. Phylogenetic analysis of 44 inbred strains ofM. douglasii derived from 23 populations with 72 RAPD markers in the nuclear DNA strongly supports this phylogeny. However, 13 chloroplast RFLPs divideM. douglasii into four distinct groups. Two of these each share one or more cpRFLPs withM. bigelovii andM. pygmaea. Several hypotheses can explain the incongruence between nuclear and chloroplast phylogeny: (1) random sorting out of chloroplasts during phylogeny from a polymorphic pool, (2) cytoplasmic introgression from the related annualM. bigelovii intoM. douglasii after hybridization followed by elimination of theM. bigelovii nuclear genome. We suggest cytoplasmic introgression as the most likely origin. Possible remnants of nuclear introgression have been found in two populations ofM. douglasii that are polymorphic for chloroplast types. In these populationsM. bigelovii type chloroplast DNA seems to be accompanied by nuclear genes for flower color and leaf shape.     

The genusPicris (Asteraceae,Lactuceae) in Tropical Africa

Three species of the genusPicris L. are native in Tropical Africa:P. abyssinica Sch. Bip. (Ethiopia),P. xylopoda Lack, spec. nova (Nigeria, Ethiopia) andP. humilis DC. (Senegal, Mali). There are indications that the two perennial species,P. abyssinica andP. xylopoda, are related to and have evolved from a primitive Central Asiatic stock in a manner parallel to many African species ofCrepis L.P. humilis, on the other hand, is a small annual plant with a high number of derived characters. The introduced species of European origin growing south of the Sahara are briefly mentioned.     

Genetic components of heterocarpy inMicroseris hybrid B87 (Asteraceae,Lactuceae)

Microseris B87 is derived from a single hybrid specimen betweenM. pygmaea with few, weakly hairy peripheral achenes and aM. bigelovii with many, strongly hairy peripheral achenes. Offspring through the F4 and F5 generations obtained by spontaneous selfing were analyzed for the segregation of quantitative and qualitative characters relating to achene dimorphism. The phenotypic effects of two previously identified unlinked genes determining the relative number of outer achenes are characterized in partially and completely homozygous sublines. We show that two morphological markers genetically linked to one of these genes are themselves regulated by the system inducing heterocarpy. Not more than two more unlinked genes are involved in the genetic basis of the heterocarpic response. The interaction of these genes in determining the heterocarpy phenotypes is discussed in the framework of a model postulating genes for a morphogen gradient across the capitulum and genes responding to this gradient.     

The use of a non-coding region of chloroplast DNA in phylogenetic studies of the subtribeSonchinae (Asteraceae:Lactuceae)

The systematic utility of sequences from a non-coding region of chloroplast DNA (cpDNA) betweenpsbA andtrnH^(GUG) was examined by assessing phylogenetic relationships in subtribeSonchinae (Asteraceae:Lactuceae). Primers constructed against highly conserved regions of tRNA genes were used for PCR amplification and sequencing. ThepsbA-trnH intergenic spacer contains several insertions and deletions (indels) inSonchinae with the length varying from 385 to 450 bp. Sequence divergence ranges from 0.00% to 7.54% withinSonchinae, with an average of 2.4%. Average sequence divergence inSonchus subg.Sonchus is 2.0%, while the mean for subg.Dendrosonchus and its close relatives in Macaronesia (the woodySonchus alliance) is 1.0%. Our results suggest that this region does not evolve rapidly enough to resolve relationships among closely related genera or insular endemics in theAsteraceae. The phylogenetic utility ofpsbA-trnH sequences of the non-coding cpDNA was compared to sequences from the ITS region of nuclear ribosomal DNA. The results suggest that ITS sequences evolve nearly four times faster thanpsbA-trnH intergenic spacer sequences. Furthermore, the ITS sequences provide more variable and phylogenetically informative sites and generate more highly resolved trees with more strongly supported clades, and thus are more suitable for phylogenetic comparisons at lower taxonomic levels than thepsbA-trnH intergenic chloroplast sequences.     

Genotype relationships inMicroseris elegans (Asteraceae,Lactuceae) revealed by DNA amplification from arbitrary primers (RAPDs)

The genetic relationships among 10 inbred lines representing 10 populations of the autogamous annualMicroseris elegans from throughout California has been determined using random amplified polymorphic DNAs (RAPDs). Seventeen arbitrary 10 base pair primers produced 134 amplification products; 81 of these were shared by two or more strains. The 3 genotypes from Northern California are closely related as are 3 genotypes from Middle Californian populations which are not nearest neighbors. DNA fingerprinting with the oligonucleotide (GATA)₄ gave compatible results, but the comparison was limited to samples run on one gel. Isoenzyme patterns are compatible with the DNA results, but limited by the very low number of informative polymorphisms. The clustered relationship among genotypes within a species and their geographic distribution suggests very restricted genetic recombination and an origin of new populations from randomly dispersed achenes within the range of the species.     

Intraspecific evolution ofMicroseris pygmaea (Asteraceae,Lactuceae) analyzed by cosegregation of phenotypic characters (QTLs) and molecular markers (RAPDs)

The Chilean annual,Microseris pygmaea, has differentiated in distinct coastal and inland series of populations after long-distance dispersal from western North America. Two plants from the most diverse biotypes were crossed, a large F₂ was raised and analysed for segregation of 30 phenotypic characters. Segregation of molecular markers (47 RAPDs, 1 RFLP, 2 isozymes) was determined in a subpopulation of 45 plants which include all extremes for the phenotypic characters. 32 marker/character cosegregations were significant at the 1% level in t-tests between dominant and homozygous recessive marker genotypes. Considering linkage among markers and pleiotropy of certain marker loci, the number of independent quantitative trait loci (QTLs) is reduced to about 18. Interactions among 2 or 3 QTLs affecting one character have been characterized. The phenotypic differentiation ofM. pygmaea during its evolution from a single founder individual begins to be understood at the level of single-gene mutants.     

Isozyme studies in the genusCheirolophus (Asteraceae:Cardueae-Centaureinae) in the Iberian Peninsula, North Africa and the Canary Islands

The phylogenetic and phenetic analysis of 109 RAPD polymorphisms inS. nebrodensis, a perennial and self-incompatible endemic of four mountain ranges in Spain, andS. viscosus, a self-compatible annual widespread in Europe, as well asS. lividus, S. sylvaticus andS. vulgaris revealed a sister group relationship between the first two species. This result contrasts sharply with the earlier hypothesis based on isozyme variation thatS. viscosus originated from within a paraphyleticS. nebrodensis and that the two species represent a progenitor-derivative pair. After considering possible reasons for the sister group relationship found, including the possibility of rooting artefacts, it is concluded that neither the RAPD data nor the isozyme data allow to draw safe conclusions about the mode of speciation and therefore the relative age of the two species. As a consequence, the limited genetic variation ofS. viscosus in comparison toS. nebrodensis as revealed by both the RAPD and the isozyme data may reflect its population history, geographical distribution, reproductive ecology, or mode of dispersal just as well as its recent origin from a paraphyleticS. nebrodensis. The result of this study calls for a critical reexamination of other taxon pairs postulated to have a progenitor-derivative relationship on the basis of isozyme evidence.     

Chloroplast and nuclear DNA variation among homozygous plants in a population of the autogamous annualMicroseris douglasii (Asteraceae,Lactuceae)

The autogamous diploid annualMicroseris douglasii of California occurs in many isolated populations. The populations consist of one to many highly inbred biotypes. Morphological variation among populations usually is greater than within populations. In spite of the virtual absence of gene flow even within populations, genetically determined character differences are randomly distributed and associated throughout the range of the species. Recent evidence even suggests introgression of chloroplasts from the relatedM. bigelovii. Offspring families from 25 plants of a very variable population were raised and examined for segregation of morphological and molecular (RAPD) markers. All 25 original plants were completely homozygous for all markers, but each differed from all others at least in some markers. The population consisted of two genetically isolated groups of plants: a distinct inbred line (3 plants) and 22 plants with random associations of a common set of markers and characters, possibly recombinant inbreds from a past hybridization event. One of these 22 plants contained a chloroplast genome found inM. bigelovii, the other 24 plants a chloroplast genome found only inM. douglasii.     

Four additive genes determining pappus part numbers inMicroseris annual hybrid C34 (Asteraceae/Lactuceae)

Microseris strain C34 is a hybrid between the Chilean speciesM. pygmaea (10 pappus parts) and the CalifornianM. bigelovii (5 pappus parts). The F1 specimen had from 5 to 10 pappus parts per achene with an average of 6. F2, F3 and F4 plants derived from this hybrid by spontaneous selfing show segregation for the average number of pappus parts. Four segregating unlinked genes could be demonstrated, each with an allele determining 5 pappus parts from thebigelovii parent, one with an allele determining 10 pappus parts, three with null alleles from thepygmaea parent. The expected average pappus part number is the arithmetic mean of the 5- and 10-determining factors. Considerable environmental and developmental influences, both random noise and systematic shifts, could be demonstrated to influence the phenotypic expression. The parallel hybrid strain B87 has two 10-alleles rather than one in itspygmaea genome. The evolution of the pappus part genes ofM. pygmaea from those of abigelovii-like ancestor seems to demand the concerted (non-independent) mutation of at least two genes.     

A second marker enzyme in the genetics of pappus part numbers inMicroseris hybrid B87 (Asteraceae,Lactuceae)

CrossingMicroseris pygmaea (10 pappus parts) withM. bigelovii (5 pappus parts) results in hybrids with variable pappus part numbers between 5 and 10. Previous work has shown that a system of four additively acting genes determines the average pappus part numbers of these hybrids. In hybrid B87 two genes have a 10-determining and a 5-determining allele each, two others a 5-determining and a null (inactive or missing) allele. Genetic linkage of one of the latter with the enzyme geneEsterase-1 and the leaf shape genespatulate leaves has been demonstrated. Here we demonstrate linkage between one of the two 10-determining genes and the enzyme locusEsterase- Y/B. The genotypes in the pappus part system of many specimens can now be fully determined. This is a major advance for the analysis of the evolution of this additive polygenic system.Genetics of Pappus Part Numbers inMicroseris Hybrid B87, II.—Part I:Bachmann & al. 1981.     

Isozyme differentiation in the endemic genusArgyranthemum (Asteraceae: Anthemideae) in the Macaronesian Islands

The genusArgyranthemum (Asteraceae: Anthemideae) comprises 38 taxa and is restricted to the archipelagos of the Canaries, Selvagens, Madeira, and Desertas in the Macaronesian biogeographic region. An electrophoretic study, including 17 enzyme loci and at least one population of each of the described taxa, was carried out. High identity (low distance) values between taxa (mean of 0.893) were obtained despite the old age of the islands, their close proximity to the African continent, and the fact thatArgyranthemum is the most species-rich and variable genus in Macaronesia. These results suggest that the genus is monophyletic and that it has evolved very rapidly in these islands. There is little correspondence between taxonomy and neighbor-joining analysis based on Roger's genetic distances, but in several instances populations from the same islands cluster together despite being from different species or even different sections. It is suggested that repeated genetic bottlenecks associated with the founding of new populations during radiation of the genus resulted in lineage sorting of ancestral allozyme polymorphisms. Because every population has a high average identity with all other populations, lineage sorting could result in populations of different taxa being slightly more similar than populations of the same taxon. Gene flow between different species on the same island could account for some populations clustering by island of origin rather than taxonomic disposition. Average allozyme diversity within populations (0.098) is 50% higher than the mean total diversity for species endemic to oceanic islands.     

Taxonomy and phylogeny of the tribePlucheeae (Asteraceae)

The tribePlucheeae (Benth.)A. Anderb., has been analysed cladistically by means of a computerized parsimony program (Hennig 86), using theArctotideae as outgroup. The results of the analysis are presented in a consensus tree and one cladogram. Four major monophyletic subgroups can be recognized: TheColeocoma group (3 genera), thePterocaulon group (3 genera), theLaggera group (6 genera), and thePluchea group (12 genera). All recognized genera are described and most genera are supplied with taxonomical notes including comments on their taxonomic status. Genera such asBlumea, Pluchea, andEpaltes are demonstrated to be unnatural assemblages.Monarrhenus andTessaria are both closely related to thePluchea complex. The old generic nameLitogyne Harv. has been taken up for one species ofEpaltes, the genusRhodogeron is reduced to a synonym ofSachsia, and the following new combinations are made;Litogyne gariepina (DC.)A. Anderb., andSachsia coronopifolia (Griseb.)A. Anderb.     

Phylogenetic and evolutionary implications of nuclear ribosomal DNA variation in dwarf dandelions (Krigia,Lactuceae, Asteraceae)

Restriction site and length variations of nrDNA were examined for 51 populations of seven species ofKrigia. The nrDNA repeat ranged in size from 8.7 to 9.6 kilobase (kb). The transcribed region, including the two ITSs, was 5.35 kb long in all examinedKrigia populations. In contrast, the size of the nontranscribed IGS varied from 3.35 to 4.25 kb. Eight different types of length-variations were identified among the 51 populations, including distinct nrDNA lengths in the tetraploid and diploid populations of bothK. biflora andK. virginica. However, a few variations were detected among populations of the same species or within a cytotype. All populations ofKrigia sect.Cymbia share a 600 bp insertion in IGS near the 18 S gene, and this feature suggests monophyly of the section. AllKrigia spp. had a conjugated type of subrepeat composed of approximately 75 basepairs (bp) and 125 bp. Base modifications in the gene coding regions were highly conserved among species. Forty-five restriction sites from 15 enzymes were mapped, 24 of which were variable among populations. Only four of the variable sites occurred in the rRNA coding region while 20 variable sites were detected in the noncoding regions. Collectively, 25 enzymes generated about 66 restriction sites in each nrDNA; this amounts to about 4.3% of the nrDNA repeat. A total of 50 restriction sites was variable, 28 of which were phylogenetically informative. Phylogenetic analyses of site mutations indicated that two sections ofKrigia, sect.Cymbia and sect.Krigia, are monophyletic. In addition, relationships among several species were congruent with other sources of data, such as cpDNA restriction site variation and morphology. Both length and restriction site variation supported an allopolyploid origin of the hexaploidK. montana. The average sequence divergence value inKrigia nrDNA was 40 times greater than that of the chloroplast DNA. The rapid evolution of nrDNA sequences was primarily due to changes of the IGS sequences.     

Karyotype evolution in South American species of Hypochaeris (Asteraceae, Lactuceae)

The genus Hypochaeris (Asteraceae, Lactuceae) contains ten species in Europe, three in Asia, and approximately 50 in South America. Previous cytotaxonomic studies have shown two groups of taxa: (1) European species with different basic chromosome numbers and differentiated karyotypes, and (2) South American species with x=4 and uniform asymmetric and bimodal karyotypes. Karyotypic data are synthesized for South American species of Hypochaeris with new information for six Chilean species: H. acaulis, H. apargioides, H. palustris, H. spathulata, H. tenuifolia and H. thrincioides. Four main groups can be distinguished based on presence and localization of secondary constrictions – SCs (bearing Nucleolar Organizer Regions – NORs) on chromosomes 2 and 3, and 18S–25S and 5S rDNA loci number, localization, and activity. We propose karyotypic evolution of South American Hypochaeris (x=4) from H. maculata-like (x=5) European ancestors. The original South American karyotype would have possessed two SCs, one on the long arm of chromosome 2, and the other on the short arm of chromosome 3 (in terminal position). Further evolution would have involved inversion within the short arm of chromosome 3 and inactivation/loss of the SC on chromosome 2.     

Chloroplast DNA restriction site variation in theVernonieae (Asteraceae), an initial appraisal of the relationship of New and Old World taxa and the monophyly ofVernonia

Chloroplast DNA restriction site variation was examined for 35 taxa in theVernonieae and four outgroup tribes, using 17 restriction enzymes mapped for ca. 900 restriction sites per species; 139 mutations were found to be phylogenetically informative. Phylogenetic trees were constructed using Wagner and weighted parsimony, and evaluated by bootstrap and decay analyses. Relationships of Old and New World taxa indicate complex geographical relationships; there was no clear geographic separation by hemisphere. The relationships between Old and New World Vernonias found here support prior morphological analyses. The sister group to all New and most Old World taxa was composed of a small group of Old World species including yellow-flowered, trinervate-leaved species previously postulated to be basal in the tribe. The majority of both New and Old World taxa are derived from a lineage beginning with the monotypic genusStokesia, an endemic of the southeastern United States. The genusVernonia was also found to be paraphyletic within both the New and Old World. Available data do not support either the separation ofVernonia or the tribeVernonieae into geographically distinct lineages. The pattern of relationships within theVernonieae for taxa from North America, Asia, Africa, Central and South America is most similar to that of several other groups of both plants and animals with a boreotropical origin, rather than an origin in Gondwanaland. Such a pattern of distribution suggests more ancient vicariant events than are routinely postulated for theAsteraceae.     

A cladistic study of North AmericanCoreopsis (Asteraceae: Heliantheae)

A cladistic study of all 44 species of North AmericanCoreopsis was performed using 35 characters. The resulting cladogram indicated that all 11 sections are monophyletic. At the intersectional level, two lineages were revealed, one consisting of six sections occurring almost exclusively in Mexico and California, and another comprising five sections restricted largely to the eastern and southeastern United States. The cladogram is similar to phylogenies produced by less explicit methods but it differs in two major respects: the monotypic sect.Silphidium is placed with other sections from the southeastern United States rather than with Mexican sections, and sect.Anathysana from Mexico is more closely allied with the three California sections than with sect.Electra from Mexico.     

The cytotaxonomy ofEmilia spp. (Asteraceae: Senecioneae) occurring in Brazil

Analysis of several populations in a large part of the distribution area of the genusEmilia in Brazil has revealed only two species: the diploidE. sonchifolia and the tetraploidE. fosbergii. The more widely reportedE. coccinea was not found. They show a karyotype constancy in morphology and chromosome number (2n = 10 and 2n = 20, respectively), C-banding pattern and number of secondary constrictions. Some indications were found thatE. fosbergii may be an allopolyploid and that its ancestors had different genome sizes.