Andrea D. Wolfe

Disintegration of the scrophulariaceae.

A molecular systematic study of Scrophulariaceae sensu lato using DNA sequences of three plastid genes (rbcL, ndhF, and rps2) revealed at least five distinct monophyletic groups. Thirty-nine genera representing 24 tribes of the Scrophulariaceae s.l. (sensu lato) were analyzed along with representatives of 15 other families of Lamiales. The Scrophulariaceae s.s. (sensu stricto) include part or all of tribes Aptosimeae, Hemimerideae, Leucophylleae, Manuleae, Selagineae, and Verbasceae (= Scrophularieae) and the conventional families Buddlejaceae and Myoporaceae. Veronicaceae includes all or part of tribes Angelonieae, Antirrhineae, Cheloneae, Digitaleae, and Gratioleae and the conventional families Callitrichaceae, Globulariaceae, Hippuridaceae, and Plantaginaceae. The Orobanchaceae include tribes Buchnereae, Rhinantheae, and the conventional Orobanchaceae. All sampled members of Orobanchaceae are parasitic, except Lindenbergia, which is sister to the rest of the family. Family Calceolariaceae Olmstead is newly erected herein to recognize the phylogenetic distinctiveness of tribe Calceolarieae. The Calceolariaceae are close to the base of the Lamiales. The Stilbaceae are expanded by the inclusion of Halleria. Mimulus does not belong in any of these five groups.

Assessing hybridization in natural populations of Penstemon (Scrophulariaceae) using hypervariable intersimple sequence repeat (ISSR) bands

Inferences regarding hybridization rely on genetic markers to differentiate parental taxa from one another. Intersimple sequence repeat (ISSR) markers are based on single‐primer PCR reactions where the primer sequence is derived from di‐ and trinucleotide repeats. These markers have successfully been used to assay genetic variability among cultivated plants, but have not yet been tested in natural populations. We used genetic markers generated from eight ISSR primers to examine patterns of hybridization and purported examples of hybrid speciation in Penstemon (Scrophulariaceae) in a hybrid complex involving P. centranthifolius, P. grinnellii, P. spectabilis and P. clevelandii. This hybrid complex has previously been studied using three molecular data sets (allozymes, and restriction‐site variation of nuclear rDNA and chloroplast DNA). These studies revealed patterns of introgression involving P. centranthifolius, but were unsuccessful in determining whether gene flow occurs among the other species, and support for hypotheses of diploid hybrid speciation was also lacking. In this study, we were able to fingerprint each DNA accession sampled with one to three ISSR primers and most accessions could be identified with a single primer. We found population‐ and species‐specific markers for each taxon surveyed. Our results: (i) do not support the hybrid origin of P. spectabilis; (ii) do support the hypothesis that P. clevelandii is a diploid hybrid species derived from P. centranthifolius and P. spectabilis; and (iii) demonstrate that pollen‐mediated gene flow via hummingbird vectors is prevalent in the hybrid complex.

Clonal diversity in the rare Calamagrostis porteri ssp. insperata (Poaceae): comparative results for allozymes and random amplified polymorphic DNA (RAPD) and intersimple sequence repeat (ISSR) markers

Four populations of the rare, highly clonal grass Calamagrostis porteri ssp. insperata were examined using allozymes and the two polymerase chain reaction (PCR)‐based markers, random amplified polymorphic DNA (RAPD) and intersimple sequence repeat (ISSR) bands. Only one of the 15 allozyme loci was variable and two alleles were detected, both of which were found in two populations, while only one genotype was detected in the other two populations. ISSR and RAPD markers detected more genotypes within populations than did allozymes. ISSR markers detected more diversity than RAPD markers in three of the four populations examined. In one population, no RAPD diversity was found whereas eight different genotypes were found among the 10 plants with ISSR markers. This diversity is present despite rare flowering, no documented occurrence of seed set in natural populations and very low seed set with experimental pollinations, all of which suggest that sexual reproduction rarely occurs. The subspecies is self‐compatible, but seed initiation is lower in selfed ovules; also, there is high embryo abortion regardless of pollen source. Variation detected by RAPD and ISSR primers may reflect higher levels of sexual reproduction in the past, very rare sexual reproduction in extant populations, somatic mutations, or a combination of the three. Although the PCR‐based markers identify several multilocus genotypes within populations, it is not known whether these all represent distinct genets generated by sexual reproduction or result from somatic mutations in the old, perennial and highly clonal plants.

Molecular Phylogenetic and Evolutionary Studies of Parasitic Plants

The parasitic nutritional mode is a frequently evolved adaptation in animals (Price, 1980), as well as in flowering plants (Kuijt, 1969). Heterotrophic angiosperms can be classified as either mycotrophs or as haustorial parasites. The former derive nutrients via a symbiotic relationship with mycorrhizal fungi. Haustorial parasites, in contrast, directly penetrate host tissues via a modified root called a haustorium and thereby obtain water and nutrients. Although such categories are often a matter of semantics, we use the term parasite in a strict sense to refer to haustorial parasites. Angiosperm parasites are restricted to the dicot subclasses Magnoliidae, Rosidae, and Asteridae; have evolved approximately 11 times; and represent approximately 22 families, 265 genera, and 4,000 species, that is, about 1% of all angiosperms (Fig. 8.1). Owing to their unique adaptations, parasitic plants have long been the focus of anatomical, morphological, biochemical, systematic, and ecological research (Kuijt, 1969; Press and Graves, 1995). For the vast majority of parasitic plants, negative effects upon the host are difficult to detect, yet others (e.g., Striga, Orobanche) are serious weeds of economically important crops (Kuijt, 1969; Musselman, 1980; Eplee, 1981; Stewart and Press, 1990; Press and Graves, 1995).

Population genetic structure of the cleistogamous plant species Viola pubescens Aiton (Violaceae), as indicated by allozyme and ISSR molecular markers

Few studies of genetic variation have focused on species that reproduce through both showy, chasmogamous (CH) flowers and self-pollinated, cleistogamous (CL) flowers. Using two different techniques, genetic variation was measured in six populations of Viola pubescens Aiton, a yellow-flowered violet found in the temperate forests of eastern North America. Results from eight allozyme loci showed that there was considerable genetic variation in the species, and population structuring was indicated by the presence of unique alleles and a θ (FST) value of 0.29. High genetic variation was also found using ISSR (inter-simple sequence repeat) markers, and population structuring was again evident with unique bands. Viola pubescens appears to have a true mixed-mating system in which selfing through CL and CH flowers contributes to population differentiation, and outcrossing through CH flowers increases genetic variation and gene flow among populations. Overall, allozyme and ISSR techniques yielded similar results, indicating that ISSR markers show potential for use in population genetic studies.

ORIGIN AND BIOGEOGRAPHY OF AESCULUS L. (HIPPOCASTANACEAE): A MOLECULAR PHYLOGENETIC PERSPECTIVE

Sequences of chloroplast gene matK and internal transcribed spacers of nuclear ribosomal RNA genes were used for phylogenetic analyses of Aesculus, a genus currently distributed in eastern Asia, eastern and western North America, and southeastern Europe. Phylogenetic relationships inferred from these molecular data are highly correlated with the geographic distributions of species. The identified lineages closely correspond to the five sections previously recognized on the basis of morphology. Ancestral character‐state reconstruction, a molecular clock, and fossil evidence were used to infer the origin and biogeographic history of the genus within a phylogenetic framework. Based on the molecular phylogenetic reconstruction of the genus, sequence divergence, and paleontological evidence, we infer that the genus originated during the transition from the Cretaceous to the Tertiary (~65 M.Y.B.P.) at a high latitude in eastern Asia and spread into North America and Europe as an element of the “boreotropical flora”; the current disjunct distribution of the genus resulted from geological and climatic changes during the Tertiary.

Relationships Within and Among Species of the Holoparasitic Genus Hyobanche (Orobanchaceae) Inferred from ISSR Banding Patterns and Nucleotide Sequences

Abstract The systematic relationships of four species in the South African holoparasitic genus Hyobanche were examined using inter-simple sequence repeat (ISSR) banding patterns and nucleotide sequence data from nuclear ribosomal ITS regions and the plastid gene rbcL. Ordination of ISSR data revealed discrete groups, although H. glabrata and H. rubra were indistinguishable. Phylogeny reconstructions based on ISSR and ITS data were congruent and depicted relationships where H. atropurpurea and H. sanguinea form a clade with H. glabrata and H. rubra as their sister group. In contrast, the rbcL tree revealed a topology where H. atropurpurea was sister to a clade that included the other three species. The combination of molecular, morphological, and biogeographical data suggest two alternative hypotheses: (1) that floral evolution has progressed from galeate hirsute corolla tubes to straight glabrous tubes as represented by H. sanguinea, H. glabrata (intermediate morphology), and H. rubra, respectively; or (2) the intermediate floral morphology and distribution of H. glabrata reveal a hybrid origin of this species with H. sanguinea and H. rubra as progenitors. Communicating Editor: Paul Wilson

Phylogeny and biogeography ofOrobanchaceae

Orobanchaceae, as it is currently defined, includes all levels of parasitic ability ranging from nonparasitic (Lindenbergia) to facultative and obligate hemiparasites to obligate holoparasites. Several genera are of economic importance as crop weeds and have been studied by scientists interested in developing methods of control, but most genera have not been studied in a comparative framework. In this study we have used ITS sequence data to build a phylogenetic framework with which to examine previous systematic hypotheses of relationships among genera, and biogeographic hypotheses of either a Cretaceous, Gondwanan or mid-Tertiary, Laurasian origin of the family. A single-most parsimonious ITS tree was produced from a combined data set of nucleotides and gap characters. Our results support the current classification ofOrobanchaceae and a hypothesis of a mid-Tertiary, Laurasian origin of the family.

Recombination, Heteroplasmy, Haplotype Polymorphism, and Paralogy in Plastid Genes: Implications for Plant Molecular Systematics

Abstract The chloroplast genome has provided sequence data for inferring plant phylogenies for more than a decade. General operational assumptions regarding chloroplast gene sequences are that they are single-copy, under strong functional constraint, and uniparentally inherited. However, studies have demonstrated the transfer of large segments of the chloroplast genome into the nuclear or mitochondrial genomes. Additionally, heteroplasmy and haplotype polymorphism of plastid genomes within and among individuals have been documented. Random sampling of nucleotide sequences from different plastid haplotypes or from paralogous sequences through the course of a systematic investigation may affect the resulting gene tree topology and the inferences drawn from it.

Anther Evolution: Pollen Presentation Strategies When Pollinators Differ

Male‐male competition in plants is thought to exert selection on flower morphology and on the temporal presentation of pollen. Theory suggests that a plant’s pollen dosing strategy should evolve to match the abundance and pollen transfer efficiency of its pollinators. Simultaneous pollen presentation should be favored when pollinators are infrequent or efficient at delivering the pollen they remove, whereas gradual dosing should optimize delivery by frequent and wasteful pollinators. Among Penstemon and Keckiella species, anthers vary in ways that affect pollen release, and the morphology of dried anthers reliably indicates how they dispense pollen. In these genera, hummingbird pollination has evolved repeatedly from hymenopteran pollination. Pollen production does not change with evolutionary shifts between pollinators. We show that after we control for phylogeny, hymenopteran‐adapted species present their pollen more gradually than hummingbird‐adapted relatives. In a species pair that seemed to defy the pattern, the rhythm of anther maturation produced an equivalent dosing effect. These results accord with previous findings that hummingbirds can be more efficient than bees at delivering pollen.