Edward E. Schilling

The tortoise and the hare II: relative utility of 21 noncoding chloroplast DNA sequences for phylogenetic analysis

Chloroplast DNA sequences are a primary source of data for plant molecular systematic studies. A few key papers have provided the molecular systematics community with universal primer pairs for noncoding regions that have dominated the field, namely trnL-trnF and trnK/matK. These two regions have provided adequate information to resolve species relationships in some taxa, but often provide little resolution at low taxonomic levels. To obtain better phylogenetic resolution, sequence data from these regions are often coupled with other sequence data. Choosing an appropriate cpDNA region for phylogenetic investigation is difficult because of the scarcity of information about the tempo of evolutionary rates among different noncoding cpDNA regions. The focus of this investigation was to determine whether there is any predictable rate heterogeneity among 21 noncoding cpDNA regions identified as phylogenetically useful at low levels. To test for rate heterogeneity among the different cpDNA regions, we used three species from each of 10 groups representing eight major phylogenetic lineages of phanerogams. The results of this study clearly show that a survey using as few as three representative taxa can be predictive of the amount of phylogenetic information offered by a cpDNA region and that rate heterogeneity exists among noncoding cpDNA regions.

INFRAGENERIC CLASSIFICATION OF HELIANTHUS (COMPOSITAE)

Summary A formal infrageneric classification for the genus Helianthus is presented. The classification was derived using phenetic, cladistic and biosystematic procedures. The 49 species of Helianthus are placed into four sections and seven series.

Phylogeny and biogeography of Eupatorium (Asteraceae: Eupatorieae) based on nuclear ITS sequence data

The classification of the predominantly Neotropical Eupatorieae depends upon the circumscription of the core genus Eupatorium. The recently proposed narrowing of Eupatorium to ∼42 species in eastern temperate North America, Europe, and eastern Asia was tested with phylogenetic analysis of nucleotide sequence variation in the internal transcribed spacer (ITS) region of nuclear ribosomal DNA. A total of 40 samples (36 species) of Eupatorieae was analyzed. Several species from North America, South America, and Eurasia that were formerly recognized within a large Eupatorium s.l. (sensu lato) were included in the study. Other taxa included were representative of the majority of the subtribes native to eastern temperate North America. Parsimony analysis supported the contention that Eupatorium be defined narrowly and suggested that Eupatoriadelphus is distinct. The tree topology suggested that Eupatorium and Eupatoriadelphus share a common North American ancestor with Liatris relative to other Eupatorieae. It was apparent that the presumed sister taxa in Eupatoriinae from South America belong to a different clade. These results suggest that, following initial divergence in North America, Eupatorium reached Europe via dispersal during the late Pliocene with subsequent radiation in Asia.

Phylogenetic Relationships in Helianthus (Asteraceae) Based on Nuclear Ribosomal DNA Internal Transcribed Spacer Region Sequence Data

The internal transcribed spacer (ITS) region of the nuclear ribosomal DNA was sequenced from 73 samples representing 46 of the 49 species of Helianthus and both species of Phoebanthus. Overall there was only a small amount of sequence divergence, less than 4% within Helianthus and less than 5.5% between Phoe- banthus and Helianthus. Phylogenetic analysis supported a close relationship between Phoebanthus and Helianthas as sister groups within subtribe Helianthinae. Within Helianthus, four species of the southeastern U.S. were separated successively as basally diverging clades: H. heterophyllus, H. carnosus, H. porteri, and H. agrestis. There was little differentiation among the remaining species. The annual species of sect. Helianthus were placed in a weakly supported clade, within which three further clades were also weakly supported: H. annuus/H. argophyllus/H. bolanderi; H. debilis/H. praecox; H. petiolaris/H. neglectus/H. deserticola/H. niveus subsp. niveus and subsp. canescens. The perennial species did not form a monophyletic clade. Within the perennials, there were a few clades of weak to moderate support: H. angustifolius/H. floridanus/H. simulans; H. giganteus/H. grosseserratus/H. maximiliani/H. nuttallii/H. divaricatus; H. arizonensis/H. ciliaris/H. laciniatus; and H. atrorubens/H. mollis/H. occidentalis/H. silphioides. The phylogenetic placement of species with narrow geographic distributions in the extreme southeastern part of North America as the sister group (Phoebanthus) and as basally diverging branches of Helianthus in the ITS trees suggests that the ancestor to the genus may have been confined to this area prior to divergence and dispersal leading to the extant array of snpecies.

Systematics of Solanum sect. Solanum (Solanaceae) in North America

Numerical taxonomic studies show that eleven species of Solanum sect. Solanum occur in North America. Five diploid (n = 12) species, S. americanum, S. douglasii, S. interius, S. pseudogracile, and S. ptycanthum are apparently native. A sixth diploid species, S. sarrachoides, is an introduction from South America. Three polyploid species, S. furcatum, S. nigrum, and S. villosum, occur infrequently. Two other polyploid species, S. scabrum and S. retrofiexum, are sometimes cultivated. A notable nomenclatural change, necessitated by a previously selected lectotype for S. americanum, is the use of the name S. americanum for the species previously known as S. nodfiorum. The name S. ptycanthum is now used for the species of the north- eastern United States formerly called S. americanum. Solanum sect. Solanum (also known as the S. nigrum complex) is a cos- mopolitan group of about 30 annual or short-lived perennial, herbaceous species of weeds. A variety of historical and biological factors combine to make the taxonomy of this section difficult (Edmonds 1979a). The use of experimental taxonomic techniques in several regional studies has clarified the taxonomy of this section in much of its range (Edmonds 1972, 1979a; Henderson 1974; Heiser et al. 1979). The present study covers the North American species of the section. Sterility of interspecific hybrids and ease of obtaining hybrids in sect. Solanum make it tempting to attempt to define species on the basis of genetic isolating mechanisms. However, the high frequency of intraspe- cific hybrid sterility and its lack of correlation with morphological diver- gence indicate that hybrid sterility is not useful in delimiting species in this section (Schilling and Heiser 1979). Because the breeding system of most species of sect. Solanum is primarily autogamous (Schilling 1978), there is probably little gene flow between populations with the result that biological species (Mayr 1963) are not present in this section. Hence, although data from crossing studies have been incorporated into this study as phenetic characters, they are not accorded any special signifi- cance as evidence of an isolating mechanism that separates species. To classify species in this section, an operational approach using techniques of numerical taxonomy to discover discontinuities by which species may be recognized has been used.

Phylogenetic reticulation in subtribe Helianthinae

Incongruence between phylogenetic estimates based on nuclear and chloroplast DNA (cpDNA) markers was used to infer that there have been at least two instances of chloroplast transfer, presumably through wide hybridization, in subtribe Helianthinae. One instance involved Simsia dombeyana, which exhibited a cpDNA restriction site phenotype that was markedly divergent from all of the other species of the genus that were surveyed but that matched the restriction site pattern previously reported for South American species of Viguiera. In contrast, analysis of sequence data from the nuclear ribosomal DNA internal transcribed spacer (ITS) region showed Simsia to be entirely monophyletic and placed samples of S. dombeyana as the sister group to the relatively derived S. foetida, a result concordant with morphological information. A sample of a South American species of Viguiera was placed by ITS sequence data as the sister group to a member of V. subg. Amphilepis, which was consistent with cpDNA restriction site data. Samples of Tithonia formed a single monophyletic clade based on ITS sequence data, whereas they were split between two divergent clades based on cpDNA restriction site analysis. The results suggested that cpDNA transfer has occurred between taxa diverged to the level of morphologically distinct genera, and highlight the need for careful and complete assessment of molecular data as a source of phylogenetic information.

Chemosystematic Investigation of the Annual Species of Helianthus (Asteraceae)

Abstract A total of 43 HPLC peaks tentatively considered to be sesquiterpene lactones was detected from a survey of the 18 taxa (eleven species and seven subspecies) of Helianthus sect. Helianthus using a recently developed microtechnique. All but one of the taxa showed characteristic sesquiterpene lactone patterns with between six and 15 compounds each. H. paradoxus appears to be the only species in the genus in which these compounds are not detectable. Comparison with available reference compounds allowed assignment of structures to 21 of the compounds. Known compounds can be classified into five major structural subtypes, the systematic distribution of which divides the section into three well-defined subgroups. The sesquiterpene lactone profiles of the other two annual species of the genus, H. agrestis and H. porteri , exhibit significant differences relative to any species of sect. Helianthus , which supports their exclusion from the section.

Sesquiterpene lactone chemistry of Zaluzania grayana from on-line LC-NMR measurements

On-line LC-NMR measurements were used for the first time to elucidate the sesquiterpene lactone chemistry of a Compositae species, Zaluzania grayana. Structure elucidation of three compounds, visible in HPLC analysis of the constituents of glandular trichomes, was performed on a leaf extract of less than a gram of dried plant tissue by means of direct coupling of the HPLC and NMR instruments. The structures could be assigned to the guaianolide zaluzanin C, a new modified guaianolide and to the 15-hydroxy derivative of costunolide. The taxonomic relevance of the identified compounds is discussed.

Evidence from chloroplast DNA restriction site analysis on the relationships of Scalesia (Asteraceae: Heliantheae)

Helianthus and later assigned to Helianthopsis. Two other groups considered as potential sister groups based on their geographic distribution in South America were not placed near Scalesia in the most parsimonious tree. Viguiera sect. Diplostichis appears to be relatively basal within subtribe Helianthinae, and the South American species of Viguiera, although previously classified in more than one subgenus, appear to form a single, monophyletic group that is not the sister group to Scalesia. The minimum of ten restriction site differences between Scalesia and Pappobolus of approximately 525 sites surveyed yielded an estimated sequence divergence of 0.19%, and an estimated time of divergence of approximately 1.96.2 million years.

Evolution of diversity in Albugo is driven by high host specificity and multiple speciation events on closely related Brassicaceae.

The Albuginaceae, responsible for white blister rust disease on various angiosperms, are obligate biotrophic oomycetes that are only distantly related to downy mildews (Peronosporaceae). Their diversity has been much underestimated during the past decades, mainly because of the paucity of morphological characters for species delimitation, which led to the application of a broad species concept. Recent phylogenetic analyses have revealed three new species within Albugo parasitic to Brassicaceae, but the overall evolution of these plant pathogens remains poorly understood. Especially the diversity of Albugo in various plant genera is almost completely unknown. Based on ITS and cox2 sequence data of 72 Albugo specimens, predominantly from herbarium archives, and focusing on the widespread genus Cardamine, a high degree of phylogenetic diversity was revealed in Albugo. In particular, the hypothesis that one host genus can be colonised by more than one white blister rust species is confirmed. In addition, it is revealed that there are hitherto overlooked lineages with close relationships to the generalist species Albugo candida. Evidence for at least three different species of Albugo infecting Cardamine is presented in this study. Based on molecular phylogenetic and morphological data three new white blister rust species are described, Albugo hohenheimia, Albugo hesleri, and Albugo leimonios infecting Cardamine hirsuta, Cardamine diphylla and Cardamine pratensis, respectively. The fact that these species each have different ecological niches, suggests that environmental factors may have played a role in the speciation process in Albugo. Our findings suggest that other larger genera of the Brassicaceae may harbour unrecognized white blister rust species and that only a small fraction of the true biodiversity of white blister rusts is known at present.