Young Accreting Compact Objects in M31: The Combined Power of NuSTAR, Chandra, and Hubble.

We present 15 high-mass X-ray binary (HMXB) candidates in the disk of M31 for which we are able to infer compact object type, spectral type of the donor star, and age using multiwavelength observations from NuSTAR, Chandra, and the Hubble Space Telescope. The hard X-ray colors and luminosities from NuSTAR permit the tentative classification of accreting X-ray binary systems by compact object type, distinguishing black hole from neutron star systems. We find hard-state black holes, pulsars, and non-magnetized neutron stars associated with optical point-source counterparts with similar frequency. We also find nine non-magnetized neutron stars coincident with globular clusters and an equal number of pulsars with and without point-source optical counterparts. We perform spectral energy distribution (SED) fitting for the most likely optical counterparts to the HMXB candidates, finding seven likely high-mass stars and one possible red helium-burning star. The remaining seven HMXB optical counterparts have poor SED fits, so their companion stars remain unclassified. Using published star formation histories, we find that the majority of HMXB candidates-X-ray sources with UV-bright point-source optical counterpart candidates-are found in regions with star formation bursts less than 50 Myr ago, and three are associated with young stellar ages (<10Myr). This is consistent with similar studies of HMXB populations in the Magellanic Clouds, M33, NGC 300, and NGC 2403.

Gamma-gamma coincidence performance of LaBr3:Ce scintillation detectors vs HPGe detectors in high count-rate scenarios.

A radiation detection system consisting of two cerium doped lanthanum bromide (LaBr3:Ce) scintillation detectors in a gamma-gamma coincidence configuration has been used to demonstrate the advantages that coincident detection provides relative to a single detector, and the advantages that LaBr3:Ce detectors provide relative to high purity germanium (HPGe) detectors. Signal to noise ratios of select photopeak pairs for these detectors have been compared to high-purity germanium (HPGe) detectors in both single and coincident detector configurations in order to quantify the performance of each detector configuration. The efficiency and energy resolution of LaBr3:Ce detectors have been determined and compared to HPGe detectors. Coincident gamma-ray pairs from the radionuclides 152Eu and 133Ba have been identified in a sample that is dominated by 137Cs. Gamma-gamma coincidence successfully reduced the Compton continuum from the large 137Cs peak, revealed several coincident gamma energies characteristic of these nuclides, and improved the signal-to-noise ratio relative to single detector measurements. LaBr3:Ce detectors performed at count rates multiple times higher than can be achieved with HPGe detectors. The standard background spectrum consisting of peaks associated with transitions within the LaBr3:Ce crystal has also been significantly reduced. It is shown that LaBr3:Ce detectors have the unique capability to perform gamma-gamma coincidence measurements in very high count rate scenarios, which can potentially benefit nuclear safeguards in situ measurements of spent nuclear fuel.

A pilot study of children's exposure to CCA-treated wood from playground equipment.

Arsenic from chromated copper arsenate (CCA)-treated wood, widely used in playgrounds and other outdoor equipment, can persist as surface residues on wood. This raises concerns about possible health risks associated with children playing on CCA-treated playgrounds. In a Pilot Study, 11 children (13-71 months) in homes with and without CCA-treated playgrounds were evaluated with post-exposure hand rinses and urine for total arsenic. Samples of wood, soil, and mulch, as well as synthetic wipes, were sampled for total arsenic. In non-CCA-treated playgrounds vs. CCA-treated playgrounds, respectively, wood arsenic was <2.0 mg/kg vs. mean arsenic 2370 mg/kg (range 1440-3270 mg/kg); soil arsenic was <3.0 mg/kg vs. mean arsenic of 19 mg/kg (range 4.0-42 mg/kg); mulch arsenic at one non-CCA-treated playground was 0.4 mg/kg vs. two CCA-treated playgrounds of 0.6 and 69 mg/kg. The arsenic removed using a synthetic wipe at non-CCA-treated playgrounds was <0.5 microg, while mean arsenic from CCA-treated wood was 117 microg (range 1.0-313). The arsenic mass from hand rinses for children who played at non-CCA-treated playgrounds was <0.2 microg, while mean arsenic mass was 0.6 microg (range <0.2-1.9) at CCA-treated playgrounds. Mean urinary total arsenic levels were 13.6 pg/ml (range 7.2-23.1 pg/ml) for all children evaluated, but there was no association between access to CCA-playgrounds and urinary arsenic levels. Arsenic speciation was not performed. This preliminary Pilot Study of CCA-treated wood playgrounds observed dislodgeable arsenic on 11 children's hands after brief periods of play exposure. Future efforts should increase the number of children and the play exposure periods, and incorporate speciation in order to discriminate between various sources of arsenic.

"Ultra-light" patient-controlled epidural analgesia during labor: effects of varying regimens on analgesia and physician workload.

BACKGROUND: Patient-controlled epidural analgesia (PCEA) offers many advantages over continuous epidural infusions for maintenance of labor analgesia. Some of these benefits may depend on the PCEA settings. This study evaluated several regimens for "ultra-light" (0.125%) PCEA with basal continuous infusion (CI) in labor with goals of minimizing physician interventions while providing good analgesia. METHODS: Two hundred and twenty ASA I-II women receiving epidural analgesia during active labor (cervical dilation <5 cm) were randomly assigned in a double-blind manner to four treatment groups (n=30 in each). Analgesia was maintained with a PCEA/CI pump using bupivacaine 0.0625% + sufentanil 0.35 microg/mL. PCEA settings were: group A: CI 10 mL/h, PCEA bolus 6 mL, 8-min lockout; group B: CI 10 mL/h, PCEA bolus 12 mL, 16-min lockout; group C: CI 15 mL/h, PCEA bolus 6 mL, 8-min lockout; group D: CI 15 mL/h, PCEA bolus 12 mL, 16-min lockout. RESULTS: In groups A, B, C and D, 76, 77, 75 and 85% of parturients respectively, required no physician rescue boluses. Pain scores were low and maternal satisfaction was high in all groups, with minimal differences among them. Spontaneous vaginal delivery occurred in 78% of patients overall, instrumental (forceps or vacuum) delivery in 10% and cesarean section in 12%. CONCLUSIONS: These ultra-light PCEA regimens provided excellent analgesia with minimal physician workload and a high spontaneous delivery rate. Use of moderate to high-volume, ultra-light PCEA/CI techniques should facilitate provision of labor analgesia in busy obstetric units.

Dynamics of mobile element activity in chalcone synthase loci in the common morning glory (Ipomoea purpurea).

Mobile element dynamics in seven alleles of the chalcone synthase D locus (CHS-D) of the common morning glory (Ipomoea purpurea) are analyzed in the context of synonymous nucleotide sequence distances for CHS-D exons. By using a nucleotide sequence of CHS-D from the sister species Ipomoea nil (Japanese morning glory [Johzuka-Hisatomi, Y., Hoshino, A., Mori, T., Habu, Y. & Iida, S. (1999) Genes Genet. Syst. 74, 141-147], it is also possible to determine the relative frequency of insertion and loss of elements within the CHS-D locus between these two species. At least four different types of transposable elements exist upstream of the coding region, or within the single intron of the CHS-D locus in I. purpurea. There are three distinct families of miniature inverted-repeat transposable elements (MITES), and some recent transpositions of Activator/Dissociation (Ac/Ds)-like elements (Tip100), of some short interspersed repetitive elements (SINEs), and of an insertion sequence (InsIpCHSD) found in the neighborhood of this locus. The data provide no compelling evidence of the transposition of the mites since the separation of I. nil and I. purpurea roughly 8 million years ago. Finally, it is shown that the number and frequency of mobile elements are highly heterogeneous among different duplicate CHS loci, suggesting that the dynamics observed at CHS-D are locus-specific.

Comparative genomics of chalcone synthase and Myb genes in the grass family.

Most plant genes occur as members of multigene families where new copies arise through duplication. Duplicate genes that do not confer an adaptive advantage to the plant are expected to rapidly erode into pseudogenes owing to the accumulation of transpositions, insertion/deletion mutations and nucleotide changes. Nonfunctional copies will drift to fixation within a few million years and ultimately erode beyond recognition. Duplicate genes that are retained over longer periods of evolutionary time must be positively selected based on some adaptive advantage conferred on the plant species. We explore the dynamics of the recruitment of new duplicate genes for chalcone synthase, the enzyme that catalyzes the first committed step of flavonoid biosynthesis, and for the myb family of transcriptional activators. Our analyses show that new chs genes are recruited into the genome of grasses at a rate of one new copy every 15 to 25 million years. In contrast, the myb gene family is much older and many duplicate copies appear to predate the separation of the angiosperm lineage from other seed plants. The general pattern suggests a rapid adaptive proliferation of new chs genes but a more ancient elaboration of regulatory gene functions. Our analyses also reveal accelerated rates of protein evolution following gene duplication and evidence is presented for interlocus exchange among duplicate gene loci.

Flower color variation: a model for the experimental study of evolution.

We review the study of flower color polymorphisms in the morning glory as a model for the analysis of adaptation. The pathway involved in the determination of flower color phenotype is traced from the molecular and genetic levels to the phenotypic level. Many of the genes that determine the enzymatic components of flavonoid biosynthesis are redundant, but, despite this complexity, it is possible to associate discrete floral phenotypes with individual genes. An important finding is that almost all of the mutations that determine phenotypic differences are the result of transposon insertions. Thus, the flower color diversity seized on by early human domesticators of this plant is a consequence of the rich variety of mobile elements that reside in the morning glory genome. We then consider a long history of research aimed at uncovering the ecological fate of these various flower phenotypes in the southeastern U.S. A large body of work has shown that insect pollinators discriminate against white phenotypes when white flowers are rare in populations. Because the plant is self-compatible, pollinator bias causes an increase in self-fertilization in white maternal plants, which should lead to an increase in the frequency of white genes, according to modifier gene theory. Studies of geographical distributions indicate other, as yet undiscovered, disadvantages associated with the white phenotype. The ultimate goal of connecting ecology to molecular genetics through the medium of phenotype is yet to be attained, but this approach may represent a model for analyzing the translation between these two levels of biological organization.

Molecular evolution of the chalcone synthase multigene family in the morning glory genome.

Plant genomes appear to exploit the process of gene duplication as a primary means of acquiring biochemical and developmental flexibility. Thus, for example, most of the enzymatic components of plant secondary metabolism are encoded by small families of genes that originated through duplication over evolutionary time. The dynamics of gene family evolution are well illustrated by the genes that encode chalcone synthase (CHS), the first committed step in flavonoid biosynthesis. We review pertinent facts about CHS evolution in flowering plants with special reference to the morning glory genus, Ipomoea. Our review shows that new CHS genes are recruited recurrently in flowering plant evolution. Rates of nucleotide substitution are frequently accelerated in new duplicate genes, and there is clear evidence for repeated shifts in enzymatic function among duplicate copies of CHS genes. In addition, we present new data on expression patterns of CHS genes as a function of tissue and developmental stage in the common morning glory (I. purpurea). These data show extensive differentiation in gene expression among duplicate copies of CHS genes. We also show that a single mutation which blocks anthocyanin biosynthesis in the floral limb is correlated with a loss of expression of one of the six duplicate CHS genes present in the morning glory genome. This suggests that different duplicate copies of CHS have acquired specialized functional roles over the course of evolution. We conclude that recurrent gene duplication and subsequent differentiation is a major adaptive strategy in plant genome evolution.

Ewing's sarcoma masquerading as osteomyelitis.

Ewing's sarcoma in the infant and young child is rare, highly malignant, and can be difficult to identify. An erroneous diagnosis of osteomyelitis may be considered first because the presentation may be similar to that of Ewing's sarcoma, and routine laboratory evaluation may not distinguish between these entities. Two such cases are presented, one involving the tibia in a 16-month-old child and another a finger phalanx in a 7-month-old child. In both cases the correct diagnosis of Ewing's sarcoma was delayed because of initial misdiagnosis of osteomyelitis. This diagnostic dilemma is summarized, and the literature reviewed. Special attention is given to recent advances in histochemistry and cytogenetics that assist in tumor identification. The conclusion highlights areas of remaining controversies for which additional study may facilitate distinction between osteomyelitis and Ewing's sarcoma.

The evolution of plant nuclear genes.

We analyze the evolutionary dynamics of three of the best-studied plant nuclear multigene families. The data analyzed derive from the genes that encode the small subunit of ribulose-1,5-bisphosphate carboxylase (rbcS), the gene family that encodes the enzyme chalcone synthase (Chs), and the gene family that encodes alcohol dehydrogenases (Adh). In addition, we consider the limited evolutionary data available on plant transposable elements. New Chs and rbcS genes appear to be recruited at about 10 times the rate estimated for Adh genes, and this is correlated with a much smaller average gene family size for Adh genes. In addition, duplication and divergence in function appears to be relatively common for Chs genes in flowering plant evolution. Analyses of synonymous nucleotide substitution rates for Adh genes in monocots reject a linear relationship with clock time. Replacement substitution rates vary with time in a complex fashion, which suggests that adaptive evolution has played an important role in driving divergence following gene duplication events. Molecular population genetic studies of Adh and Chs genes reveal high levels of molecular diversity within species. These studies also reveal that inter- and intralocus recombination are important forces in the generation allelic novelties. Moreover, illegitimate recombination events appear to be an important factor in transposable element loss in plants. When we consider the recruitment and loss of new gene copies, the generation of allelic diversity within plant species, and ectopic exchange among transposable elements, we conclude that recombination is a pervasive force at all levels of plant evolution.

Histologic correlation with magnetic resonance imaging for benign and malignant lipomatous masses.

Purpose/results. We evaluated the diagnostic accuracy of magnetic resonance imaging (MRI) for 46 consecutive patients with lipomatous soft tissue tumors prior to biopsy and resection. Twenty-eight patients had benign lipomas and 18 had liposarcomas. Clinical differences between thdse patients with benign disease and those with malignant lesions were average age at the time of presentation (49 years for benign vs 62 years for malignant, p < 0.001) and average length of symptoms prior to resection (64 months for benign versus 38 months for malignant, p = 0.01). MRI characteristics associated with benign disease included: smaller tumor size (9.4 cm average greatest dimension for benign lesions vs 13.4 cm for malignant masses, p = 0.022); a mass with a uniformly homogeneous signal (p = 0.0003); a mass with homogeneous high T1 and T2 signals and a low short-time-inversion-recovery (STIR) signal comparable to normal fat (p < 0.0001). This last signal pattern was not seen in malignant lesions (0/18) and was present in almost all benign lipomas (25/28). The usual MRI descriptions of soft tissue masses such as infiltrating vs encapsulating, deep vs subcutaneous and septated vs non-septated were not helpful predictors of malignancy in this series. Needle biopsies of lipomatous masses with heterogeneous signals on MRI resulted in inaccurate diagnoses due to sampling error in 5/9 patients.Discussion. A carefully planned and performed MRI study of lipomatous masses can accurately predict a benign lipoma whenever a homogeneous high T1 and T2, as well as a low STIR, signal is present. However, a mass with any other signal characteristics must be biopsied carefully in order to make an accurate diagnosis.

Change in junior high school students' AIDS-related knowledge, misconceptions, attitudes, and HIV-preventive behaviors: effects of a school-based intervention.

A school-based AIDS-prevention program for junior high school students was developed and implemented in an inner-city area in northern California that serves predominantly African-American and Asian students. The curriculum, taught by science teachers, consisted of twelve classroom sessions using both didactic and interactive exercises covering sex education, HIV biology, drug use, decision-making and refusal skills, and public response to AIDS and community resources. Changes from baseline of self-reported responses to questions on pre- and posttests concerning AIDS knowledge and misconceptions, tolerance toward persons with AIDS, and high-risk behaviors were compared between intervention and control schools. Students in the intervention schools had a significant increase in AIDS knowledge (p < .0001) and became more tolerant of people with AIDS (p < .001) compared with students in the control school. Changes in high risk behavior could not be detected, perhaps due to the small number of sexually active students (24% of the sample). Students who increased their AIDS knowledge (p < .0001) as a result of the intervention became more tolerant of people with AIDS. A school-based HIV-prevention curriculum, taught by trained classroom teachers, can modify middle adolescents' HIV-related knowledge about the casual transmission of HIV, and their attitudes toward persons with AIDS.

Evolution of the chalcone synthase gene family in the genus Ipomoea.

The evolution of the chalcone synthase [CHS; malonyl-CoA:4-coumaroyl-CoA malonyltransferase (cyclizing), EC 2.3.1.74] multigene family in the genus Ipomoea is explored. Thirteen CHS genes from seven Ipomoea species (family Convolvulaceae) were sequenced--three from genomic clones and the remainder from PCR amplification with primers designed from the 5' flanking region and the end of the 3' coding region of Ipomoea purpurea Roth. Analysis of the data indicates a duplication of CHS that predates the divergence of the Ipomoea species in this study. The Ipomoea CHS genes are among the most rapidly evolving of the CHS genes sequenced to date. The CHS genes in this study are most closely related to the Petunia CHS-B gene, which is also rapidly evolving and highly divergent from the rest of the Petunia CHS sequences.

Neighborhood wellness centers: collaboration between home care & nursing education.

There is growing evidence of the cost benefit of health promotion and disease prevention services for the older adult population. A nursing education program and a home care agency have come together to provide this valuable service to older adults in the community while educating the next generation of nursing professionals to do the same.

Factors associated with multiple sex partners among junior high school students.

Twenty-one percent of a sample of inner-city junior high school students were found to be sexually active (n = 403). Only 31% of them reported a single lifetime sexual partner, 25% reported two partners, and 43% reported three or more partners. Logistic regression analysis evaluated the influence of demographic, psychosocial, and behavioral factors on the adolescents' lifetime number of sex partners. Respondents whose sexual debut occurred before age 13 years were nine times more likely to report three or more sex partners compared with those whose first sexual intercourse was at age 15 or 16 years, blacks were four times more likely than non-Hispanic whites to report three or more sex partners; and males were four times as likely as females to report this number of sexual partners. Factors not independently associated with the number of sex partners included: age, Asian or Hispanic ethnicity, human immunodeficiency virus (HIV) knowledge, self-efficacy (belief that one can protect oneself from the virus), condom use, and alcohol and drug use. We conclude that a significant proportion of school-based middle adolescents are sexually active and that most of these are at risk for contracting HIV because of behaviors such as having multiple sexual partners. Topics often stressed in school-based HIV education, such as factual knowledge about HIV, avoiding drugs and alcohol, and condom use are not associated with adolescents' choice about their number of sex partners. Intervention programs will have to identify and then target each specific HIV risk behavior and its motivations in order to reduce adolescents' risks of contracting and transmitting the disease.

Evolution of a noncoding region of the chloroplast genome.

The relative rate of occurrence of nucleotide substitutions versus indel (insertion/deletion) events is investigated by comparing complete DNA sequence data from the noncoding portion of the chloroplast genome that maps between the genes rbcL and atp beta. The sequence data are obtained from nine species that represent three tribes of the grass family. Indels could be categorized by those that are deletions or duplications of adjacent or proximal sequences and those that do not appear to be permutations of adjacent sequences. The first category represents 82% of the recorded indels. These indels may also be characterized by being direct duplications of one to several bases usually within runs of As or Ts or by being duplications or deletions of more complex sequences. When viewed from within groups of closely related taxa, indel events appear to occur at an equal or slightly faster rate than do nucleotide substitution events. However, the apparent rate of accumulation of indels in more distantly related species is significantly slower than that of nucleotide substitutions. This difference in apparent accumulation rates between indel events and nucleotide substitutions suggests that the proportion of superimposed changes has been higher among all indel events than among all nucleotide substitution events. Indeed the indels involving more complex sequences were found to be confined across taxa to a number of highly labile sites. Independent, though similar, indel events occur at identical sites in unrelated taxa, yet may not be shared among related taxa, resulting in a type of molecular parallelism. As a result, the phylogenetic tree based on indel events represents an evolutionary hypothesis which is inconsistent with the accepted phylogeny of these grasses. The phylogenetic tree based on nucleotide substitutions is consistent with accepted phylogeny.

Determinants of condom use among junior high school students in a minority, inner-city school district.

Condoms reduce the risk of human immunodeficiency virus (HIV) transmission; however, their use among adolescents has been inconsistent. Little is known about factors which motivate consistent condom use, particularly among younger adolescents. In a study designed to identify such factors, 1899 inner-city junior high school students were surveyed. In June 1988, students completed an anonymous self-report questionnaire assessing HIV-related knowledge, attitudes, and behaviors. Among sexually active students (N = 403), logistic regression analysis evaluated the influence of demographic, psychosocial, and behavioral factors on frequency of condom use. Respondents who believe condoms are effective in preventing HIV transmission were 2.2 times more likely to report using condoms consistently during sexual intercourse; those with low perceived costs associated with condom use were 1.9 times more likely to be consistent users. Number of lifetime sexual partners was inversely related to frequency of condom use. Respondents with a history of three or more sex partners were half as likely to use condoms consistently. Factors not associated with consistent condom use include age, age at sexual debut, ethnicity, HIV knowledge, perceived efficacy to avoid HIV infection, and alcohol and drug use. School- and community-based HIV prevention programs will have to go beyond the didactic transfer of factual information and include more interactive teaching strategies to improve adolescents' attitudes toward condoms are self-efficacy to increase condom use and to counter negative peer influences and adolescents' perceptions of invulnerability. Physicians are an underutilized source of HIV prevention information. They have an important role in counseling adolescents about effective HIV-prevention methods and dispelling misperceptions which hinder consistent condom use.

AIDS knowledge, attitudes, and behavior among inner city, junior high school students.

To gain information about AIDS knowledge, attitudes, and behavior of junior high school students, 1,967 students in three junior high schools in an inner city school district were surveyed. Ages of the participants ranged from 11-16 years, and 48% were male. Ethnically, 33% were Asian, 31% African-American, 24% Latino, and 5% white. African-American students had greater AIDS general knowledge than Asians and similar general knowledge to Latinos and whites. Most students wanted to be taught about AIDS in school. Misconceptions about casual contagion of AIDS were common. Students with these misconceptions were more likely to believe that students with AIDS should not be allowed to attend school. A high proportion of students had engaged in high-risk behavior including sexual intercourse, drinking alcoholic beverages, and using street drugs. More boys than girls reported each of these activities. Of individuals having had sexual intercourse, a positive association was found between the belief that condoms are effective in preventing HIV infection and use of condoms. These findings support the possibility that improving knowledge about HIV transmission would result in more tolerance toward students with HIV infection and would result in less high-risk behavior.

PIP: In June 1988, researchers analyzed data from 1235-1882 questionnaires concerning AIDS knowledge, attitudes, and behavior among inner city, junior high school students [90% ethnic minorities, especially Blacks (61%)] in San Francisco, California to get baseline data so educators could design relevant AIDS prevention programs geared toward minorities. Asians knew less about AIDS than Blacks (p.001), Latinos (p.001), and Whites (p.001). Most students knew what activities were high risk for acquiring HIV, but up to 50% often thought HIV could also be transmitted via casual contact. The students who had such beliefs were more likely to believe that students with AIDS should not be allowed to come to school (p.001-.05). Boys (42%) were more likely to have had sexual intercourse than girls (18%; p.001). Further they tended to use street drugs more (11% vs. 5%; p.001). More Blacks claimed to have sexual intercourse than Latinos (p.001), Asians (p.001), or Whites (p.01). On the other hand, whites reported significantly higher drug use than Blacks (p.001), Asians (p.001), and Latinos (p.01). More boys believed condoms hindered pleasure than girls regardless of level of sexual activity. 25% of the boys found it difficult to find places that sells condoms compared to 18% of girls (p.01). 59% of all students, especially girls (p.001), said that their often was disagreement about using condoms or not with their sex partners. Sexually active students who believed condoms prevent transition of HIV (80%) used them more often than those who believed they work a little (47%; p.01). 89% wanted AIDS education in school, especially those who believed it unlikely or not possible to contract AIDS from casual contact (p.001). In conclusion, AIDS education course designers should consider anxiety about peer pressure and sexual matters since anxiety could hinder acquiring and retaining information about AIDS prevention thereby preventing adolescents from planning for the consequences of sexual contact and drug use.

rbcL sequence divergence and phylogenetic relationships in Saxifragaceae sensu lato.

Phylogenetic relationships are often poorly understood at higher taxonomic levels (family and above) despite intensive morphological analysis. An excellent example is Saxifragaceae sensu lato, which represents one of the major phylogenetic problems in angiosperms at higher taxonomic levels. As originally defined, the family is a heterogeneous assemblage of herbaceous and woody taxa comprising 15 subfamilies. Although more recent classifications fundamentally modified this scheme, little agreement exists regarding the circumscription, taxonomic rank, or relationships of these subfamilies. The recurrent discrepancies in taxonomic treatments of the Saxifragaceae prompted an investigation of the power of chloroplast gene sequences to resolve phylogenetic relationships within this family and between the Saxifragaceae and other major plant lineages. Sequence data from the gene rbcL (ribulose-1,5-bisphosphate carboxylase, large subunit) reveal that (i) Saxifragaceae sensu lato is at least paraphyletic, and probably polyphyletic, (ii) the genera Parnassia and Brexia are only distantly related to other members of Saxifragaceae, and (iii) representatives of the Solanaceae (subclass Asteridae) appear more closely related to Saxifragaceae (subclass Rosidase) than traditionally maintained. These data illustrate the value of chloroplast gene sequence data in resolving genetic, and hence phylogenetic, relationships among members of the most taxonomically complex groups.