Isozyme evidence and the origin ofSenecio vulgaris (Compositae)

An electrophoretic survey of isozyme variation was conducted to test the hypothesis thatSenecio vulgaris L. (2n = 40) is of autotetraploid origin fromS. vernalis Waldst. & Kit. (2n = 20). It was established thatS. vulgaris exhibited fixed heterozygosity at three loci examined, showed disomic inheritance at all polymorphic loci, and contained a gene (Est-1) and an allele (Aat-3b) which were not present in the single population ofS. vernalis surveyed. From this it is concluded thatS. vulgaris is not of autotetraploid origin. Instead, the genetic evidence is in keeping with an allopolyploid origin ofS. vulgaris with the possibility thatS. vernalis acted as one of its two parents.     

Chloroplast DNA and isozyme evidence on the evolution ofSenecio vulgaris (Asteraceae)

Chloroplast DNA (cpDNA) and isozyme variation were analyzed over a range of populations of two infraspecific taxa of the tetraploidSenecio vulgaris. The isozyme data were supportive of the hypothesis that the weedy and cosmopolitanS. vulgaris var.vulgaris is an evolutionary derivative ofS. vulgaris subsp.denticulatus from the coasts of W Europe and montane altitudes in S Spain and Sicily. The two taxa exhibited a very high genetic identity with subsp.denticulatus containing slightly more isozyme diversity than was found in var.vulgaris. — Three cpDNA haplotypes (A, B, C) already known from other Mediterranean diploid species ofSenecio were resolved in var.vulgaris, and an additional fourth haplotype (E) was found in subsp.denticulatus. Two alternative hypotheses were chosen to account for the origin and maintenance of the observed cpDNA composition ofS. vulgaris. It either reflects (1) the retention of an ancestral polymorphism which stems from the recurrent and polytopic formation of ancestral tetraploid lineages; or (2)S. vulgaris originally was characterized by haplotype E, and haplotypes A, B and C were acquired through repeated introgressive hybridization with related diploid species. The finding that very low levels of nuclear (isozyme) diversity were present in both taxa ofS. vulgaris examined supports the second of these two hypotheses; however, more detailed analysis of nuclear genetic diversity is required before a firm conclusion can be reached on this matter.Dedicated to emer. Univ.-Prof. DrFriedrich Ehrendorfer on the occasion of his 70th birthday     

The anthers of Senecio vulgaris (Asteraceae): saltatory evolution caught in the act

Anthers of the common annual weed, Senecio vulgaris, show an incomplete development of the two adaxial pollen sacs (microsporangia, MS). One or both adaxial MS can be missing, or they are replaced by sterile lobes. The reduction is stronger in the derived subspecies, S. vulgaris var. vulgaris than in the ancestral subspecies, S. vulgaris ssp. denticulatus. This character in S. vulgaris differs from the usual complete reduction of adaxial MS in other, independent instances of disporangiate anthers in the Asteraceae. It corresponds to the transition phenotypes associated with various recombinant genotypes derived from artificial crosses between tetrasporangiate (4 MS) and disporangiate (2 MS) species in the Asteracean genus Microseris. Senecio vulgaris could be a rare natural instance of homozygosity for a major gene permitting reduction of the adaxial MS in which the expression of the reduced phenotype is determined by different numbers of modifiers in the two subspecies.     

Biology of afroalpineDendrosenecio (Asteraceae)

The genusDendrosenecio (giant groundsels), encompassing three species and 12 subspecies, is endemic to the high mountains of East and Central Africa where it constitutes the most conspicuous components of the afroalpine vegetation. Two lifeforms, the arborescent and the prostrate rhizomatous, are regarded as the results of evolution from forest-living woody or herbaceous ancestors. Due to the uninterrupted growth period in the tropics, there are no anatomical or morphological features which allow conventional age determination. However, stem elongation rates have been determined (3–5.5 cm per year) and indicate an age of about 250 years for the tallest arborescent Dendrosenecios which may reach a height of 10 m. 30 to 120 large leaves are clustered in an enormous terminal rosette, justifying the term giant rosette plants. A leaf bud, consisting of about as many developing leaves as the rosette contains, is found in the center. During the nocturnal frost period the adult rosette leaves form a so-called night-bud by nyctinastic upwards bending and thus protect the leaf bud from freezing by insulation. The stem is surrounded by a mantle of persistent dead leaves; this ameliorates the microclimate of the pith-cells which greatly contribute to water transport into the leaves. Below the leaf rosette a zone of putrefaction is found, from where the decay of the dead leaves apparently provides nutrients directly to the growing stem. The population dynamics of the arborescentD. keniodendron is characterized by a simultaneous inflorescence development at irregular intervals of up to more than twenty years. Due to sporadic flowering and a seedling survival rate of less than 1%, oscillations of the population size are to be expected.     

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.     

Phenotypic plasticity inCrepis tectorum (Asteraceae)

Two experiments were carried out using two different approaches to compare populations ofCrepis tectorum (Asteraceae). One was based on a comparison of means of various vegetative and reproductive characters and another was based on a comparison of response patterns of the same characters in a series of environments. Population divergence within two earlier recognized form series, one from weed habitats and one from alvar habitats on Baltic islands, resulted in a partially overlapping pattern in cluster analyses based on character means. However, the pattern revealed by a comparison of the direction and amount of plastic response suggested that populations within the two form series had more similar response patterns than other combinations of populations. It was concluded that patterns of plasticity may provide useful additional information on the overall similarity among taxa. An hypothesis that plants in weed populations should exhibit a greater phenotypic response to the environments than plants in alvar populations was rejected.     

Karyological notes onCentaurea sect.Acrocentron (Asteraceae)

The karyology ofCentaurea sect.Acrocentron is surveyed. 19 chromosome counts on 8 species are reported; those onC. acaulis, C. crocata, C. galianoi, C. pubescens, andC. malinvaldiana are new. The basic chromosome numbers of the section are x = 11 and x = 10. Karyological arguments have been used to show that evolution was from x = 11 to x = 10. This is supported by biogeographical data. Two main centres of diversification of sect.Acrocentron were studied from that point of view: the East and the Southwest Mediterranean region.     

Molecular evidence that fireweed (Senecio madagascariensis, Asteraceae) is of South African origin

ITS1 sequence data was obtained for fireweed (Senecio madagascariensis) andS. lautus from Australia,S. madagascariensis andS. inaequidens from South Africa andS. madagascariensis from Madagascar. Despite the low level of variation (0.0–3.4%), these data further resolve the controversy concerning the identity and origin of fireweed. They confirm that fireweed is part of the South AfricanS. madagascariensis/S. inaequidens complex, and indicate that the infestation in Australia originated from South Africa as opposed to Madagascar. This will facilitate a resumption of biological control efforts in Australia and will direct surveys for control agents to South Africa.     

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.     

Taxonomy ofCarminatia (Asteraceae,Eupatorieae)

A taxonomic study of the largely Mexican genusCarminatia is rendered. It is comprised of three closely related species:C. tenuiflora, C. recondita andC. anomala spec. nova. Illustrations, dot maps, keys to species and complete synonymy are presented.     

The evolution of self-fertility inCrepis tectorum (Asteraceae)

The extent of self-fertility was examined in 16 populations ofCrepis tectorum. A hypothesis that a weedy habit favours autogamy was only partly supported. Low levels of self-fertility characterized non-weedy populations from calcareous grasslands (alvars) on the Baltic island in Öland. By contrast, plants in nearly all weed populations studied were more or less self-fertile. However, the trend towards autogamy may have occurred independently of the trend towards a weedy habit, as shown by moderately to high levels of self-fertility in alvar populations from two other Baltic islands. In the weed group, there was a tendency for plants from two field populations to be more autogamous than plants from more ruderal habitats. There was an association between self-fertility and small, inconspicious heads in the alvar group but the association was weaker when weed populations were also considered. The relatively wide heads characterizing the ruderal weed populations may, at least partly, be an indirect effect of increases in overall plant size and/or in the size of the fruit associated with each flower.     

Revision ofVerbesina sect.Pseudomontanoa (Asteraceae)

Verbesina sect.Pseudomontanoa is revised. The last treatment of the group byRobinson & Greenman (1899) recognized 5 species; the present treatment recognizes 12 species, 3 of which (V. breedlovei, V. cronquistii andV. olsenii) are described as new. A key to species, phyletic diagram and distribution maps are provided.     

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 karyotypes ofMicroseris bigelovii,M. douglasii,andM. pygmaea (Asteraceae)

The karyotypes of the three annuals,Microseris bigelovii, M. douglasii andM. pygmaea, consist of 2n = 18, small, submetacentric chromosomes. Length, centromere position, C-banding pattern, silver staining of NOR's, and the use of base specific fluorochromes, allow the identification of four of the nine chromosome pairs. The banding pattern ofM. bigelovii andM. pygmaea is identical, but intraspecific differences are found between strains ofM. douglasii.     

Geographical variation and genetic analysis of leaf shape inCrepis tectorum (Asteraceae)

Canonical variate analysis of plants raised in a uniform environment was used to study the pattern of geographical variation in leaf shape ofCrepis tectorum (Asteraceae). The diversity in leaf shape was much greater among populations confined to areas with exposed bedrock in the Baltic region than among weed populations scattered throughout Europe and Canada. A Ward's clustering linked outcrop populations from the archipelago of SW. Finland and the islands of Öland (Sweden) and Saaremaa (Estonia) due to the deeply lobed leaves characterizing these populations, while outcrop populations along the coast of E. Sweden were grouped due to their weakly lobed, narrow and dentate leaves. Most of the weed populations were grouped together but there was no tendency for the variation in this group to be related to habitat or geographical location. A mosaic of variation reflected in sharp (random) differentiation among local populations was superimposed on the large-scale ecogeographical pattern.—Crossing data indicated that most of the variation in degree of leaf dissection is governed by one major gene with deeply lobed leaves dominant over weakly lobed leaves. I suggest that the simple pattern of inheritance may have favoured rapid evolutionary changes in leaf shape, particularly in the Baltic area which emerged relatively late from the sea. Genetic correlations may have constrained the pattern of variation at higher taxonomic levels, since some of the trait associations detected in a segregating F₂ generation were also found at the among-population level.     

Systematic study of the genusDelilia (Asteraceae,Heliantheae)

A taxonomic study of the genusDelilia is presented. Two species are recognized:D. biflora, a widespread weed of tropical and subtropical regions of the New World, extending from Mexico to northern Argentina and recently introduced in the Cape Verde Islands; andD. repens, endemic to the Galapagos islands. A key to the species, illustrations, distribution maps, and complete synonymy are presented.     

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.     

A cladistic analysis of the tribeAstereae (Asteraceae) with notes on their evolution and subtribal classification

TheAstereae were surveyed and the genera arranged in 23 informal groups. The generic groups were used to sample representative genera for a cladistic analysis based on morphological characters. The resulting cladogram was used for discussion of evolution and subtribal classification within the tribe. The lower basic chromosome numbers x = 4, 5, 6, and 8 are interpreted as reductions from a primitive x = 9. The subtribeGrangeinae occupies a phylogenetically basal position as sister group to the rest of the tribe. This may be divided into two large groups, largely corresponding to the homochromousSolidagininae and to the heterochromousAsterinae sensu lato, i.e. including theBellidinae, Hinterhuberinae, Conyzinae, andBaccharidinae. The latter four subtribes are derived within theAsterinae, and hence reduced to synonymy. Several intercontinental relationships indicate that a geographical subdivision of the tribe should be avoided, although in our analysis most of the groups proved to be restricted to one of five major regions.