Flavonoid aglycones from leaf resins of two species of Heterotheca (compositae)

Twenty-nine flavonoid aglycones have been identified from two populations each of Heterotheca grandiflora and H. psammophila. Considerable qualitative variation was found between populations of the same species. Overall, H. grandiflora is more complex in its flavonoid profile, accumulating a total of 24 compounds based on eight skeletal types, compared with 13 compounds based on four skeletal types in H. psammophila.     

Exudate flavonoid aglycones of Veronica: Ecological and systematic implications

A survey on the distribution of surface flavonoid aglycones in 52 samples of 29 species of Veronica resulted in detection of eight flavone aglycones. Apigenin and luteolin were the most common constituents of the studied exudates, followed by the methylated derivatives apigenin 4′-methyl ether, apigenin 7,4′-dimethyl ether and luteolin 3′-methyl ether. Some intraspecific variations and the main ecological trends of flavonoid aglycone accumulation in Veronica were discussed. The observed exudate profiles appeared to be characteristic for some related groups within the genus, in agreement with the morphological, karyological, molecular and other chemical data.     

Prenylated flavonoids from the aerial parts of Dorstenia mannii

Four new prenylated flavanones, dorsmanins 1, J and epi-dorsmanins F, G, identified, respectively, as 6,7-(2,2-dimethylpyrano)-8-prenyl-5,3',4'-trihydroxyflavanone, 6,7-(2,2-dimethyldihydropyrano)-8-prenyl-5,3',4'-trihydroxflavanone, and 2'-epimers of dorsmanins F and G were isolated from the aerial parts of Dorstenia mannii together with 13 known flavonoids: 4-hydroxylonchocarpin, 4-methoxylonchocarpin, 6-prenylchrysoeriol, 6,8-diprenyleriodictyol, gancaonin P and dorsmanins A-H. The structures of these secondary metabolites were determined by spectroscopic means and by comparison with published data and with authentic specimens for some of the known compounds.     

Delayed autonomous self-pollination in Hibiscus laevis (Malvaceae)

Delayed autonomous self-pollination allows outcrossing to occur while also ensuring that seeds are produced in the absence of pollen vectors. We investigated variation in the efficacy of this pollination mechanism in populations of Hibiscus laevis. Recurvature of stylar branches occurred after 1 d of anthesis, and in plants from Ohio, Illinois, Arkansas, and Oklahoma this behavior resulted in autonomous selfing (surprisingly, stylar movement was facultative in that it did not take place when the stigmas were already pollinated). In contrast to these more northern populations, the distance between anthers and stigmas was too great to allow autonomous selfing in plants from Texas, Mississippi, and Louisiana. Greenhouse studies of plants from Ohio demonstrated that autonomous selfing resulted in an average of 29.5 seeds per flower, as compared to 59.9 seeds per flower from hand-pollination of stigmas with self pollen. In an assessment of the possible significance of this selfing mode, emasculated flowers did not set significantly fewer seeds in a natural stand in Ohio, suggesting that few seeds resulted from autonomous selfing at that site. Modest inbreeding depression was detected at this population. Our results suggest that delayed autonomous selfing is more common in northern populations, where it may facilitate population establishment and persistence at times when pollinators are scarce.     

Lipophilic Phenolics from the Leaves of Empetrum nigrum — Chemical Structures and Exudate Localization

In the course of continuing studies on the occurrence and chemical composition of lipophilic exudates on plant surfaces, the leaves of Empetrum nigrum have been studied. They were found to produce a considerable amount of lipophilic material which mostly consists of phenolic compounds. We here report the identification of two dioxygenated chalcones, three dioxygenated dihydrochalcones, and two dihydrophenanthrene derivatives. Exept for one chalcone, all these compounds were found for the first time as natural products. The upper and lower epidermis of the rolled hypostomatous leaves bear glandular trichomes. By flavonoid specific staining it can be shown that these natural products are accumulated within the capitate glandular cells.     

Flavonoid aglycones in the resin of Hazardia squarrosa var. Grindelioides

Thirty three flavonoid aglycones have been identified from the external stem and leaf resin of Hazardia squarrosa var. grindelioides by TLC co-chromatography with authentic samples. The occurrence of compounds with oxygenation at C-6 and C-5′, which are also found in the genus Haplopappus, supports the previously believed close relationship between these two genera.     

Firmiana (Malvaceae: Sterculioideae) fruits from the Upper Miocene of Yunnan,Southwest China

A new species of Firmiana Marsili is recognized and described based on capsules from the Late Miocene Lincang flora of Yunnan, China. Firmiana yunnanensis nov. sp. is represented by opened, dehiscent, membranous follicles with a weak, sinuous midvein, obtuse secondary veins and thick marginal vein. The follicles conform in shape and venation with those of extant species of Firmiana, a genus now distributed in eastern Africa, Indo-Malaysia, and eastern and southeastern Asia. This fossil species occurred within the native distribution of extant Firmiana species. It provides new information on fossil history, paleoecology, as well as on the plant diversity of the Lincang flora.     

8,14-Secopregnane glycosides from the aerial parts of Asclepias tuberosa

Twenty pregnane glycosides, tuberoside A₁–L₅, were isolated from the diethyl ether-soluble fraction of the MeOH extract from the aerial parts of Asclepias tuberosa (Asclepiadaceae). The pregnane glycosides were composed of 8,12;8,20-diepoxy-8,14-secopregnane as aglycon, and d-cymarose, d-oleandrose, d-digitoxose and/or d-glucose as the component sugars. Their structures were established using NMR spectroscopic analysis and chemical methodologies.     

HPLC analysis of leaf surface flavonoids for the preliminary classification of birch species

Flavonoid aglycones found on the surfaces of birch (Betula spp.) leaves may constitute up to 10% of the dry weight of the leaf. A facile extraction and HPLC procedure has been developed that can be used for the preliminary classification of birch species according to the patterns of their leaf surface flavonoids. The procedure involves no complex sample preparation steps, and is able to provide HPLC chromatograms from fresh leaves in less than 30 min. If necessary, leaves do not even need to be removed from the tree. Since the genus Betula is taxonomically complex and separation of different birch species can be problematic, the developed method was applied to 15 Betula species and four sub-species of Betula pendula Seven of the studied species were classified as B. pubescens and eight as B. pendula-type birches. The remaining four species did not belong to either of these two classes on account of their unique pattern of external flavonoids. The difference between the leaf surface flavonoid composition of B. pubescens and B. pendula type birch species was unambiguously clear, and the developed method could reliably distinguish between the two species. Whilst leaf surface flavonoids can be valuable chemotaxonomic markers, they classify birch species differently from morphological markers. Birch species with diploid chromosome sets did not contain any of the flavanones that were present in the leaves of other species. The close relationship between the occurrence of some flavonoid aglycones and the ploidy level of Betula species suggests that these chemotaxonomic markers may be useful both in taxonomic and phylogenetic analyses.     

Two flavonoids and other compounds from the aerial parts of Centaurea bracteata from Italy

The flowering aerial parts of Centaurea bracteata Scop. (Asteraceae) have been studied for the first time. Nineteen compounds were isolated and identified, namely a sterol glucoside, two phenolic acids, three quinic acid derivatives, and 13 flavonoids, two of which, are new natural products. Structural elucidation was performed mainly by mean of FABMS, 1D and 2D NMR spectroscopy.     

Limited effects of soil nutrient heterogeneity on populations of Abutilon theophrasti (Malvaceae)

An experiment was conducted to determine if spatial nutrient heterogeneity affects mean plant size or size hierarchies in experimental populations of the weedy annual Abutilon theophrasti Medic. (Malvaceae). Heterogeneity was imposed by alternating 8 × 8 × 10 cm blocks of low and high nutrient soil in a checkerboard design, while a homogeneous soil treatment consisted of a spatially uniform mixture of the two soil types (mixed soil). Populations were planted at three densities. The effect of soil type on the growth of individuals was determined through a bioassay experiment using potted plants. The high nutrient, low nutrient, and mixed soil differed in their ability to support plant growth as indicated by differences in growth rates and final aboveground biomass. Concentrations of N, K, P, and Mg, measured at the end of the growing season in the experimental plots, also differed among all three soil types. Nevertheless, nutrient heterogeneity had little effect at the population level. Mean maximum leaf width measured at midseason was greater for populations on heterogeneous soil, but soil treatment did not affect midseason measurements of plant height, total number of leaves per plant, or canopy width. Population density affected all these parameters except plant height. When aboveground biomass was harvested at the end of the growing season, soil treatment was found to have no main effect on mean plant biomass, total population biomass, the coefficient of variation in plant biomass, or the combined biomass of the five largest plants in the population, but mean plant biomass was greater for populations on heterogeneous soils at the intermediate planting density. Mean plant biomass, total population biomass, and the coefficient of variation in plant biomass all varied with planting density. Mortality was low overall but significantly higher on homogeneous soil across all three densities. Soil heterogeneity had its strongest effect on individuals. In heterogeneous treatments plant size depended on the location of the plant stem with respect to high and low nutrient patches. Thus, soil nutrient heterogeneity influenced whether particular individuals were destined to be dominant or subordinate within the population but had little effect on overall population structure.     

Iridoids from the aerial parts of Verbena littoralis (Verbenaceae)

The iridoids, 6S-hydroxy-8S-methyl-4-methylene-hexahydro-cyclopenta[c]pyran-3-one and 6S,9S-dihydroxy-8S-methyl-4-methylene-hexahydro-cyclopenta[c]pyran-3-one, were isolated from the aerial parts of Verbena littoralis. Their structures and stereochemistry were elucidated by means of NMR spectral data analysis. Both compounds showed moderate in vitro activity against gram positive and negative bacteria as well as moderate in vivo intestinal peristaltic action in mouse. The iridoids also showed moderate free radical scavenging activity against l,l-diphenyl-2-picrylhydrazyl (DPPH) as well as antioxidant activity, the latter being evidenced by redox properties measured using E1CD-HPLC.     

Taxonomic characters of the staminal tube and epicalyx in Brazilian Pavonia (Malvaceae)

This study was based on the analysis of staminal tube and epicalyx morphology of species ofPavonia (Malvaceae) from northeastern and southeastern Brazil. The importance of characters in the infrageneric taxonomy is discussed. In general, the variability in staminal tube and epicalyx characters are useful mainly in separating closely related species and a few sections; these characters, however, cannot be used to separate subgenera.