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.     

Patterns of intraspecific variation inAntennaria alborosea,A. corymbosa,A. marginata,A. microphylla,A. parvifolia,andA. umbrinella (Asteraceae:Inuleae)

Patterns of intraspecific variation were examined inAntennaria alborosea A. E. Porsild,A. corymbosa E. Nels,A. marginata Greene,A. microphylla Rydb.,A. parvifolia Nutt., andA. umbrinella Rydb. AlthoughA. alborosea was initially considered arctic in distribution, it became apparent that a southern montane element also exists. Our results suggest that morphological differences between arctic and southern montane specimens represent clinal variation. The additional morphological data for specimens that occur more than 1,500 km south of the species' range as it was initially described result in a better understanding of this once presumed arctic taxon. Morphological variation in the dioecious speciesA. corymbosa, A. marginata, A. microphylla, A. parvifolia, andA. umbrinella was greater between the genders than was geographic variation within each gender. These results demonstrate that both pistillate and staminate specimens must be examined in dioecious species ofAntennaria if morphological variation in the respective species is to be fully understood. Character size or number of broadly distributed species (A. microphylla andA. parvifolia) generally decreased with increasing longitude, whereas characters of species with more restricted distributions (A. alborosea, A. corymbosa, andA. marginata) generally increased in size or number with increasing latitude or longitude.Antennaria umbrinella was an exception in this respect.     

Gene lineage analysis in populations ofHelianthus niveus andH. petiolaris (Asteraceae)

Helianthus petiolaris andH. niveus are polytypic species which are morphologically distinct at the periphery of their ranges but intergrade in areas of sympatry.Helianthus niveus includes both annual and perennial members, whereasH. petiolaris is strictly annual. Chloroplast DNA and nuclear ribosomal DNA restriction site data were used to reconstruct the evolutionary history of populations of the two species. Cladistic analyses reveal the following: (1) neither species is monophyletic; (2) the annual habit is derived once in this complex; and (3) the region of morphological intergradation appears to be primary in origin. The significance of interbreeding versus common descent in defining species concepts is discussed in relation to the above cladistic analyses.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

Intergenic spacers of rRNA genes in three species of theCynareae (Asteraceae)

Intergenic spacers of the rRNA genes of three species of theCynareae tribe:Cynara cardunculus subsp.scolymus (artichoke),Onopordum acanthium, andO. illyricum were cloned in the plasmid pGEM-7zf(+). Detailed restriction mapping and partial sequencing of the IGSs were carried out. The structural analysis showed a clear diversity betweenCynara andOnopordum, while a high degree of homology was found between the twoOnopordum spp. In all three species a fragment of about 450 bp from the 5 end of 18S to the Acc I site with a high sequence homology was present. Nucleotide sequences upstream from the above mentioned Acc I site show a gradual decrease of homology betweenCynara andOnopordum.     

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.     

Invasive tapetum and tricelled pollen inAmbrosia trifida (Asteraceae,tribeHeliantheae)

Staminate flowers of giant ragweed,Ambrosia trifida L. (Asteraceae, tribeHeliantheae, subtribeAmbrosiinae) were processed into resin and sectioned 1–2 µm thick. The invasive (amoeboid) anther tapetum remains parietal until microspores are released from tetrads, then it swells and invades the locule, merging gradually into a single protoplast that flows among the microspores. After the tapetal membrane ruptures at late microspore stage, tapetal debris fills the locule, then disappears as pollen matures. Pollen becomes tricelled before anthesis. The two sperm cell nuclei are slender and wormlike. The present report supports the two generalizations that invasive tapetum and tricelled pollen are attributes of theAsteraceae.     

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.     

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.     

Allozymic and morphometric variation inLemna minor (Lemnaceae)

Allozymic and morphometric variation was studied in 28 clones ofLemna minor. This variation was compared with the corresponding variation in four clones ofLemna gibba and four clones ofSpirodela polyrrhiza. A high level of allozymic variation was observed among the clones, despite having been grown under uniform laboratory conditions for several years and despite its quasi-exclusive clonal means of propagation. Based on degree of allozymic similarity,Spirodela polyrrhiza was distinguished from the twoLemna species but the latter species were genetically indistinguishable. Allozymic similarity among clones ofLemna minor was not related to morphometric similarity, nor was it related to the degree of geographic separation or climatic similarity of their sites of origin. The results suggest that allozymic variation among these clones ofLemna minor may be largely neutral and not a consequence of differential selection.     

A comparison of the pollen wall ultrastructure of aureoid and non-aureoidSenecio species (Asteraceae) in North America

The structure of the pollen wall as revealed by transmission electron microscopy is presented for 29 speciesSenecio including 19 aureoid and ten non-aureoid species. The previous report of a helianthoid wall structure (exine with internal foramina) is confirmed for all the aureoid species examined while all of the non-aureoid taxa showed a senecioid pattern. The data provide support for the treatment of the aureoid complex as a distinct taxon.