Flavonoids of Plummera: Taxonomic implications at the generic level within the gaillardiinae

Four populations each of Plummera floribunda and P. ambigens were examined for flavonoid content. Six compounds were isolated and identified as flavone and flavonol aglycones and flavonol glycosides. In all cases, both taxa were found to be identical in flavonoid content. Plummera was then compared to other genera in the subtribe Gaillardiinae. At the present time, it is the opinion of the author that Plummera is very closely related to, but not congeneric with Hymenoxys.     

The effect of interplant distance on mating success in federally threatened, self-incompatible Hymenoxys herbacea = H. acaulis var. glabra (Asteraceae)

We investigated large- and fine-scale effects of interplant distance on compatibility, seed set, and seed germination in a rare, self-incompatible perennial, Lakeside daisy (Hymenoxys herbacea = H. acaulis var. glabra). Plants were collected at the Marblehead Peninsula. Ohio, and transplanted to a greenhouse where they were hand-pollinated. For the large-scale analysis, 110 crosses were classified in three categories: Near crosses (0.75-6.70 m), Far crosses (17-72 m), and Very Far crosses (>900 ml. There was no significant effect of interplant distance on compatibility, seed set, or seed germination in these crosses. For the fine-scale analysis, we made 44 crosses with interplant distances ranging from 0.75 to 10 m. At this scale, interplant distance explained 10.9% of the variance of the seed/floret ratio, suggesting that local genetic structure may result in a modest amount of biparental inbreeding. We found no fine-scale effects of interplant distance on compatibility or percentage of seed germination, but it is possible that biparental inbreeding could affect later stages of the life cycle not included in this study. For all distance classes, >80% of the crosses were compatible, indicating that lack of compatibility between mates is not likely to limit seed production. Apparently, presumed population bottlenecks have not been severe enough for genetic drift to eliminate substantial numbers of self-incompatibility alleles.     

Antimicrobial activities of sesquiterpene lactones and inositol derivatives from Hymenoxys robusta

Six compounds from the aerial parts of the Argentinean plant Hymenoxys robusta (Rusby) Parker were isolated and their structures elucidated using extensive spectroscopic analyses. These compounds comprise two inositol derivatives and four 3,4-seco-pseudoguaianolides, including vermeerin. Bioactivity assays of these compounds against bacterial and fungal pathogens showed that only vermeerin possessed antimicrobial activity specific against Staphylococcusaureus, and showed no toxicity when exposed to human-derived macrophages.     

Small populations are mate-poor but pollinator-rich in a rare, self-incompatible plant, Hymenoxys herbacea (Asteraceae)

If pollinators or compatible mates are scarce, plants in small populations may be pollen-limited and consequently produce fewer offspring. However, determining the relative importance of the genetic vs ecological mechanisms limiting successful pollination is challenging. We explored the relationships among population size, population connectivity, pollinator visitation, allozyme diversity, mate availability (measured as percent compatible crosses among plants within a population), and pollen limitation in 12 populations (N = 39-885,274) of the self-incompatible plant Hymenoxys herbacea in Ontario, Canada. Unexpectedly, small populations had more insect flower visitors per capitulum than large populations. Consistent with the effects of genetic drift, both allozyme polymorphism and mate availability decreased with decreasing population size. Pollen limitation was low and significant in only one population and could not be predicted based on knowledge of population size, connectivity, compatible mate availability, or pollinator visitation. Population size had detectable effects on both pollinator activity and mate availability. However, because the effect of population size was complementary on these two potentially limiting mechanisms, this threatened plant was rarely pollen-limited.