A SIX-YEAR STUDY OF FLAVONOID DISTRIBUTION IN A POPULATION OF LASTHENIA CALIFORNICA (ASTERACEAE)

A population of the annual Lasthenia californica in the Jasper Ridge Biological Preserve (of Stanford University) showed three major flavonoid pigment types (A, B and C; a fourth was seen in very low frequencies). The three more common types exhibited a suite of aurone and chalcone glucosides and a set of highly polar flavonoid glucuronides. Type C consisted solely of the base array; type B added luteolin 7-glucoside to the base array, while type A exhibited the base array plus eriodictyol 7-glucoside and flavonol 3,7-diglycoside bisulfates. The rare type D profile resembled type A except that the diglycosides were not sulfated. Collections were made along one of several fixed transects annually from 1982 to 1987. The main transect studied (Transect No. I) can be divided into two distinct parts on the basis of a changeover of flavonoid pattern from a mixture of types B and C at one end to exclusively (or very nearly) type A at the other. The frequencies of types B and C varied from year to year with type C predominating every year. The frequency of type A plants remained remarkably stable over the six-year period. Collections along other transects showed a similar constancy of both frequencies of the flavonoid types and location of the types along the transects. Growth experiments in a greenhouse showed that seeds from type A parents harvested in the field produced only type A progeny, while type B and C plants gave only type B and C progeny with type C predominating (a single type A progeny plant was obtained from a type C parent). Flavonoid diversity in L. californica appears to be genetically controlled and is influenced significantly by the flavonoid chemistry of the seed parent.     

VARIATION OF NUCLEAR DNA CONTENT IN HELIANTHUS ANNUUS (ASTERACEAE)

Nuclear 2C DNA content was determined by laser flow cytometry for 13 diploid (2n = 34) lines (cultivated varieties and inbred lines) of Helianthus annuus. Mean DNA amount of second leaf nuclei varied from 6.01 to 7.95 pg (32%) among lines. Mean DNA content varied up to 19% within lines. Variability in mean DNA content exceeding 27% and 48% was detected among leaves from different nodes of plants of the open-pollinated variety, Californicus, and the inbred line, RHA 299, respectively. The root tip and shoot tip nuclei of H. annuus have been reported to consist of a mixture of aneuploid (17 to 33 chromosomes) and diploid (34 chromosomes) cells, a condition called aneusomaty. Chromosome counts of root tips and an analysis of the distribution of DNA content of large numbers of nuclei from leaves indicate that aneusomaty either does not occur, or is not common, among the lines investigated. The intraspecific, intraline, and intraplant variation in DNA content in H. annuus support the concept that a sizable portion of a plant genome is unstable and subject to rapid changes in DNA amount.     

FLAVONOID DIVERSIFICATION IN THE ACHILLEA AGERATIFOLIA AND A. CLAVENNAE GROUPS (ASTERACEAE)

The Achillea ageratifolia and A. clavennae groups (Asteraceae, tribe Anthemideae) were investigated for intra- and interspecific leaf flavonoid variation. Numerous flavonoid glycosides, mostly unidentified, and variously methylated free aglycones based on scutellarein, 6-hydroxyluteolin, quercetagetin, and 6-hydroxy-kaempferol were detected. The distribution of methylated aglycones among individuals of A. ageratifolia was used to model the putative biosynthetic pathways. Several steps in the biosynthesis probably involve enzymes (methyltransferases) with strict positional specificities and broader substrate specificities. Geographical patterns in the flavonoid content of A. ageratifolia were only partly consistent with the current concept of A. ageratifolia. Different flavonoid profiles in A. ageratifolia do not appear to be of crucial importance in its adaptation to different habitats. The species of the A. clavennae group were clearly separable on flavonoid profiles and the presence of a hybrid population was supported by the flavonoid data. Interspecific differences in number of glycosides in relation to the number of free aglycones are discussed.     

NUCLEAR DNA CONTENT VARIATION IN HELIANTHUS (ASTERACEAE)

Nuclear 2C DNA content was microspectrophotometrically determined for 19 diploid (2n=34) species of Helianthus L. DNA amount varied over a fourfold range. Helianthus neglectus had the lowest (53.40 ± 0.51 Feulgen absorbancy units [FAU]) and H. agrestis the highest (216.30 ± 2.30 FAU) DNA content. Chromosome size ranged from 1.1–1.7 μm long in H. neglectus to 3.2-5.0 μm long in H. agrestis. When the highly divergent H. agrestis was excluded from analyses, the mean of the annual species (70.05 FAU) was significantly different from the mean of the perennials (97.70 FAU). No correlations of DNA content with habitat, soil type, annual precipitation, or geographical location were apparent among species.     

VARIATION AND LOCALIZATION OF FLAVONOID AGLYCONES IN HELIANTHUS ANNUUS (COMPOSITAE)

Flavonoid aglycone variation within Helianthus annuus, a species widely distributed throughout North America, was analyzed. Flavonoid aglycones of H. annuus consist of two types, flavones and chalcones. The flavone aglycones are sequestered in glandular trichomes that occur on both leaf surfaces, whereas the chalcone aglycones appear to be incorporated in the waxy leaf cuticle. Considerable variation in flavonoid profile was observed with some plants exhibiting as few as one, and others as many as seven of the eight aglycones detected. No definable phytogeographic patterns were observed for this flavonoid variation. Flavonoid aglycone variation also did not differentiate the infraspecific taxa within H. annuus.     

PHYLOGENETIC IMPLICATIONS OF CHLOROPLAST DNA RESTRICTION SITE VARIATION IN THE MUTISIEAE (ASTERACEAE)

Phylogenetic relationships among 13 species in the tribe Mutisieae and a single species from each of three other tribes in the Asteraceae were assessed by chloroplast DNA restriction site mapping. Initially, 211 restriction site mutations were detected among 16 species using 10 restriction enzymes. Examination of 12 of these species using nine more enzymes revealed 179 additional restriction site mutations. Phylogenetic analyses of restriction site mutations were performed using both Dolio and Wagner parsimony, and the resulting monophyletic groups were statistically tested by the bootstrap method. The phylogenetic trees confirm an ancient evolutionary split in the Asteraceae that was previously suggested by the distribution of a chloroplast DNA inversion. The subtribe Barnadesiinae of the tribe Mutisieae is shown to be the ancestral group within the Asteraceae. The molecular phylogenies also confirm the paraphyly of the Mutisieae and provide statistical support for the monophyly of three of its four currently recognized subtribes (Barnadesiinae, Mutisiinae, and Nassauviinae). The fourth subtribe, Gochnatiinae, is shown to be paraphyletic. Within the subtribes, several closely related generic pairs are identified. Chloroplast DNA sequence divergence among genera of the Asteraceae ranges between 0.7 and 5.4%, which is relatively low in comparison to other angiosperm groups. This suggests that the Asteraceae is either a relatively young family or that its chloroplast DNA has evolved at a slower rate than in other families.     

EVOLUTIONARY IMPLICATIONS OF INTRASPECIFIC CHLOROPLAST DNA VARIATION IN DWARF DANDELIONS (KRIGIA; ASTERACEAE)

Intraspecific chloroplast DNA polymorphisms were examined for 51 populations of seven species in the genus Krigia. A total of 1,100 restriction sites was surveyed and 46 of these were variable at the intraspecific level. Twenty-two of the variable sites were found within K. virginica, giving this species one of the highest levels of intraspecific chloroplast DNA divergence of any examined species. In contrast, no restriction site variation was detected within K. dandelion, K. wrightii, and K. occidentalis. Five polymorphisms were identified from the 16 populations of the K. cespitosa-gracilis complex, but no mutations distinguished the K. cespitosa and K. gracilis types. Krigia montana and K. biflora showed 11 and eight restriction site polymorphisms, respectively. The chloroplast genome of the hexaploid K. montana was derived from the diploid K. biflora rather than the tetraploid K. montana. High levels of polymorphism were found in species having different ploidy levels, such as K. virginica, K. biflora, and K. montana. Furthermore, most mutations found in these three species were recorded from the tetraploid lineages. As a result, evolutionary rates between different ploidy levels differ significantly. The chloroplast DNA restriction site data suggest that all surveyed populations of the autotetraploid K. virginica originated from a common ancestor. Our results also indicate that certain regions of the chloroplast genome have changed more rapidly than others and have the potential to resolve evolutionary questions at the population level.     

SYSTEMATIC IMPLICATIONS OF CHLOROPLAST DNA VARIATION IN THE SUBTRIBE MICROSERIDINAE (ASTERACEAE: LACTUCEAE)

Phylogenetic relationships among six of the seven currently recognized genera of the subtribe Microseridinae were examined using comparative restriction site mapping of the chloroplast genome. Complete cleavage maps of 17 enzymes were constructed for 35 of the 46 species in the subtribe and six representative outgroup species from four other subtribes of the Lactuceae. A total of 373 restriction site mutations was detected, 180 of which were phylogenetically informative. The chloroplast DNA mutations were used to generate phylogenetic trees using Dollo, Wagner, and weighted parsimony, and the resulting monophyletic groups were evaluated by the bootstrap method. The results indicate that the Microseridinae is paraphyletic because Stephanomeria is nested within the six core genera of the subtribe. Five of the genera of the Microseridinae are monophyletic, whereas Microseris is paraphyletic because one of its species, M. lindleyi, is more closely related to Agoseris and Nothocalais. The distant relationship of M. lindleyi to the rest of the species of Microseris is enigmatic, especially in view of its known involvement in the origin of two allotetraploid species, M. decipiens and M. heterocarpa. The taxonomic implications of these results lead to a revised classification of Microseris in which the genus Uropappus is revived to accommodate M. lindleyi, and a new genus, Stebbinsoseris, is described to include the allotetraploids. The cpDNA phylogeny is used to evaluate the patterns of character evolution within the Microseridinae, as well as to test previous hypotheses that differences in generation time result in unequal rates of chloroplast DNA evolution.     

INHERITANCE OF NUCLEAR 2C DNA CONTENT VARIATION IN INTRASPECIFIC AND INTERSPECIFIC HYBRIDS OF MICROSERIS (ASTERACEAE)

Nuclear DNA content varies over 20% within the diploid (2n = 18) species M. douglasii and M. bigelovii. Two different intraspecific crosses were made between M. douglasii biotypes which differed by about 10% in 2C nuclear DNA content. The F₂ progeny of one intraspecific cross showed no striking evidence of segregation for DNA content. The mean DNA contents of F₂ progeny from two sister hybrids from the second intraspecific cross were significantly different at the 1% level. An interspecific cross was made between biotypes of M. douglasii and M. bigelovii that differed by approximately 10% in DNA amount. The 12 F₁ progeny did not cluster around the parental midpoint, but instead encompassed nearly the entire range between the parental means. The five families of F₂ progeny studied each had a mean DNA content corresponding to that of the particular F₁ from which they were derived, indicating that the F₁ plants were not of identical DNA content. The results of this study suggest that DNA sequences which account for the DNA content differences among the plants are unstable and can undergo deletion or amplification in a hybrid. The altered DNA content may be heritably stable and show little or no segregation in the F₂ progeny.     

CAPITULUM PHYLLOTAXIS AND NUMERICAL CANALIZATION IN MICROSERIS PYGMAEA (ASTERACEAE: LACTUCEAE)

The positions at which floret primordia arise in developing capitulum buds of Microseris pygmaea D. Don have been mapped by computer-assisted light microscopy. The primordia can be assigned positions along a basic phyllotactic spiral with a divergence angle of about 137.5°. In addition, there are regular deviations from a spiral arrangement. Typically, the first 26 primordia in phyllotactic sequence are arranged in two concentric circles of 13 primordia with considerable deviations in the divergence angle and in the distances between primordia along a parastichy at positions 13 and 26. This arrangement can be simulated by geometric models that include nearest neighbor packing, together with spiral phyllotaxis. The circular arrangement of peripheral primordia at nearly equal radial distances from the center of the developing capitulum helps to explain the numerical constancy (canalization) of peripheral structures, especially the constant number of 13 inner phyllaries on heads with very different numbers of florets.     

CHARACTERIZATION OF INVASIVE CONYZA SPECIES (ASTERACEAE) IN EUROPE: QUANTITATIVE TRAIT AND ISOZYME ANALYSIS

The genus Conyza (Asteraceae) represents one of the foremost examples of intercontinental plant invasions from the New World to the Old World that has resulted in a number of taxonomic problems owing to the dearth of knowledge concerning the biosystematics of the genus. In this study, quantitative trait and enzyme electrophoresis analysis was used to assess the pattern of variation within and among five short-lived taxa of Conyza (C. blakei, C. bonariensis, C. canadenis, C. floribunda, C. sumatrensis), introduced into Europe, and to test the hypothesis of a recent hybrid origin of C. floribunda. The five taxa exhibit marked differences in morphological and life-history characteristics that are concordant with divergence in genes encoding isozymes. In addition, a recent hybrid origin of C. floribunda is clearly not supported by either quantitative or electrophoretic data. These findings suggest that the five taxa differentiated genetically in their native range prior to their introduction in Europe. As formerly suggested by Arthur Cronquist (Bulletin of the Torrey Botanical Club 70: 629–632, 1943), C. canadensis appears to be more closely related to the genus Erigeron than the other taxa. The electrophoretic results also confirm that this particular species is diploid, while the presence of multiple bands and fixed heterozygosity demonstrates that the other Conyza taxa are all genetic allopolyploids. Both quantitative and electrophoretic data suggest the presence of two groups among the polyploid taxa: one comprising C. bonariensis and C. sumatrensis, the other C. blakei and C. floribunda. The latter grouping is supported by the observation that C. blakei and C. floribunda, both native to Argentina, exhibit a striking ability to shift from semelparous to iteroparous reproduction, while the other taxa are strictly semelparous.     

SYSTEMATIC SIGNIFICANCE OF CHROMOSOME NUMBERS IN ACMELLA (ASTERACEAE)

Chromosome counts are reported for 372 individuals from 202 populations in 26 taxa of Acmella (Asteraceae: Heliantheae). Chromosome numbers for 15 taxa are first reports. A review of previous counts and the new reports supports a basic chromosome number of 13 for the genus. The results show that polyploidy, sometimes accompanied by hybridization and asexual reproduction, is widespread in Acmella and has contributed to the taxonomic difficulties in the genus. These factors have produced a variable polyploid pillar complex in sect. Acmella. In one taxon in this complex, A. oppositifolia var. oppositifolia, intrataxon and even intrapopulational chromosomal variation has been detected. Morphological studies in conjunction with observations of meiotic pairing suggest that most polyploids are alloploid in origin. The occurrence of polyploidy in 16 of the 27 taxa known chromosomally emphasizes the important role this process has had in speciation within Acmella. Although intrataxon chromosomal variation has limited the taxonomic utility of chromosome numbers, a few examples are presented in which these data have been valuable for separating some pairs of closely related taxa (A. decumbens var. affinis from var. decumbens and A. poliolepidica from A. oppositifolia).     

兰科舌唇兰属的一新亚属

笔者曾在1994年发表的“兰科植物区系中一些有意义属的地理分布格局的研究”一文中介绍了 此新亚属——显柱舌唇兰亚属的分布格局及其与舌唇兰亚属的区别。现将它正式发表。此新亚属含12种,其中1种为新组合种。     

LIFE HISTORY VARIATION WITHIN POPULATIONS OF AN ASEXUAL PLANT,ERIGERON ANNUUS (ASTERACEAE)

Genetic variation was measured for several morphological and life history characters in Erigeron annum, a triploid and obligately apomictic species. There was significant genetic variation for nearly all characters measured, including plant size, growth rate, time of flowering, biomass allocation to roots and shoots, seed weight, and germination response to temperature. Variance among genotypes accounted for up to 55% of the total phenotypic variance, well within the range of heritabilities observed for sexual species. These estimates of broad-sense heritability predict substantial short-term response to selection on life history characters in this asexual species.     

CHLOROPLAST DNA RESTRICTION SITE VARIATION AND THE PHYLOGENY OF COREOPSIS SECTION COREOPSIS (ASTERACEAE)

Restriction site variation in chloroplast DNAs (cpDNAs) of Coreopsis section Coreopsis was employed to assess divergence and phylogenetic relationships among the nine species of the section. A total of fourteen restriction site mutations and one length mutation was detected. Cladistic analysis of the cpDNA data produced a phylogeny that is different in several respects from previous hypotheses. CpDNA mutations divide the section into two groups, with the two perennial species C. auriculata and C. pubescens lacking any derived restriction site changes. The other seven species are united by five synapomorphic restriction site mutations and the one length mutation. These seven species fall into three unresolved clades consisting of 1) the remaining three perennial species, C. grandiflora, C. intermedia, and C. lanceolata; 2) three annual species, C. basalis, C. nuecensoides, and C. nuecensis; and 3) the remaining annual, C. wrightii. The cpDNA data suggest that, although the perennial habit is primitive within the section, the annual species of section Coreopsis have likely not originated from an extant perennial species. The estimated proportion of nucleotide differences per site (given as 100p) for the cpDNAs of species in the section ranges from 0.00 to 0.20, which is comparable to or lower than values reported for other congeneric species. The low level of cpDNA divergence is concordant with other data, including cross compatibility, interfertility and allozymes, in suggesting that species of the section are not highly divergent genetically.     

HERITABILITY OF CARBON ISOTOPE DISCRIMINATION IN GUTIERREZIA MICROCEPHALA (ASTERACEAE)

The carbon isotope composition (¹³C/¹²C) of C₃ plant tissues provides a long-term, integrated measure of photosynthetic metabolism. Quantitative genetic methods were used to study the inheritance of carbon isotope composition and several morphological characters in Gutierrezia microcephala, a short-lived desert perennial. Open-pollinated seed was collected from a population located near Lee's Ferry, Arizona, in an area that was disturbed approximately 20 years ago. Seeds were germinated and seedlings grown in a common greenhouse environment. Carbon isotope discrimination (Δ) and all morphological characters varied significantly among maternal families. Heritability of Δ was estimated as 81% in the greenhouse and as 92% using the regression of family mean Δ on parent Δ from field samples. Using both field and greenhouse data, we estimated a lower bound for heritability in nature of 54%. Offspring size and biomass both showed significant, positive correlations with Δ. The corresponding genetic correlations were similar in magnitude and direction, but did not differ significantly from zero. These results imply the existence of heritable differences in physiology associated with carbon assimilation and water loss within populations, and the potential for microevolutionary change through natural selection.     

AN ANALYSIS OF VARIABILITY IN SEED SETTLING VELOCITIES OF SEVERAL WIND-DISPERSED ASTERACEAE

Dispersal is an important life history component. Seed settling velocity may be a useful surrogate for the measurement of dispersal ability in wind-dispersed plants, particularly those whose seeds have plumose dispersal structures. I measured settling velocities on seeds of eight species of Asteraceae, including annuals, biennials, and perennials, and including both native and introduced species. The species are Aster exilis, Picris echioides, Chrysopsis villosa, Heterotheca grandiflora, Conyza bonariensis, Sonchus oleraceous, Senecio vulgaris, and Taraxacum officinale. From these data I estimated components of total variation in seed settling velocities due to differences among species, among plants within species, and among inflorescences and seeds within plants. Significant amounts of variability were found at all levels. Contrasts among mean settling velocities showed that the five introduced species have lower settling velocities than the three native species; this result continues to be true when annuals are considered separately from biennials and perennials. Also, over all eight species, annuals have lower settling velocities than biennials and perennials. Variability among species apparently reflects different dispersal “strategies” employed by the species; these different strategies may be correlated with other life-history traits and with ecological characteristics. Variability within species also may have ecological consequences in that such variability may represent an example of risk-spreading.     

VARIATION IN GERMINATION RESPONSE TO TEMPERATURE IN RUBBER RABBITBRUSH (CHRYSOTHAMNUS NAUSEOSUS: ASTERACEAE) AND ITS ECOLOGICAL IMPLICATIONS

Seed collections from 72 rubber rabbitbrush populations occupying a range of habitats in western North America were incubated at 3 C in the laboratory. Collections from warm desert habitats required less than 2 weeks to achieve 90% relative germination under these conditions, while collections from montane habitats showed delayed germination requiring up to 20 weeks. When 13 representative collections were incubated at constant temperatures from 5 to 30 C, all germinated completely at 30 C within 4 weeks. Collections from warm desert habitats germinated rapidly over the whole range of temperatures. Montane collections sometimes exhibited dormancy at intermediate temperatures (15 and 25 C) even though they were ultimately able to germinate at lower temperatures. Results suggest that dormancy is conditional and temperature-dependent in this species. Chilling the seeds extends the temperature range for germination downward to include the chill temperature itself. Germination response to temperature and its variation as a function of habitat are of apparent adaptive significance, serving to time germination so that the probability of seedling survival is maximized in each habitat. Within populations, response to temperature varied as a function of year of harvest and of within-year harvest date, indicating that germination patterns are probably not under rigid genetic control but represent an integration of genetic and environmental factors.