Reproductive Strategy, Performance, and Population Dynamics of the Introduced Weed Black Henbane (Hyoscyamus niger)

Determining whether and how to manage an introduced species requires basic ecological and biological knowledge. If a decision is made to actively manage an invader, doing so efficiently and effectively is critical. Basic biological or ecological information can be key in designing effective and cost-efficient management approaches. We used a greenhouse experiment and observational field studies of naturalized populations to study the modes of pollination, fecundity in the field, seed ecology, population dynamics, and demography of the introduced and toxic weed, black henbane. We showed that henbane was able to self-pollinate. Furthermore, outcrossing did not increase number or size of seeds. Plants in the sampled populations produced an estimated average of 25,300±4,004 seeds by the middle of the growing season. We found no difference in the viability of field-collected seeds that were 1 to 4 yr old. The number of flowering plants in a population was best predicted by the number of rosettes at that location in July of the previous year. The probability of rosettes surviving over the winter to reach reproductive maturity increased with precipitation and growing degree days. Total population sizes fluctuated dramatically between years. Henbane populations are ephemeral, but with large seed banks, outbreaks are possible if conditions are right. Given that this weed is toxic to livestock and humans, it is important to identify infestations and manage populations.

Introduced North American Black Henbane (Hyoscyamus niger) Populations are Biennial

Black henbane can be either annual or biennial. We investigated which life cycle is found in four introduced western North American populations. Plants were grown in a greenhouse common garden until half were vernalized by exposure to natural winter temperatures, while the other half remained in the greenhouse above 20 C, with 16 h of light and 8 h of dark. In total the plants were monitored 313 d after germination. We measured whether plants bolted, the time it took for bolting to commence, and the size at bolting. All vernalized plants bolted after 117 d of active growth (within 26 d of the end of the vernalization treatment), whereas only 26% of the nonvernalized plants bolted after an average of 278 d of active growth. Vernalized plants bolted at a smaller size than the nonvernalized plants that bolted (28 vs. 41 leaves on average). In the nonvernalized plants, the relationship between time to bolting and size was strong, but not so with the vernalized plants. Our results indicate that introduced black henbane plants are biennial, and that vernalization is more critical to bolting and flowering than reaching a certain size. Nonetheless, the fact that nonvernalized plants were capable of bolting if grown long enough suggests that vernalization is not the only cue that can trigger reproduction in introduced populations.

Influence of gibberellins on flower formation in Hyoscyamus niger L.

Gibberellins (GA₄₊₇) and gibberellin-like substances isolated from generatively induced black henbane (<em>Hyoscyamus niger</> L.) bring about the growth of shoots and a partial differentiation of axillary meristem in black henbane plants grown under non-inductive light conditions. Long-lasting application of gibberellins, however, did not result in full development of flowers in the majority of the plants investigated. Thus, it seems, that gibberellins are not specific flowering hormones in black henbane - a long-day plant.

Competitive Ability of Black Henbane (Hyoscyamus niger) When Grown with Three Native Grasses

Black henbane is a poisonous, invasive plant in the family Solanaceae, and is typically associated with highly disturbed environments, such as pipelines, roadsides, and mammalian burrows. Often, such disturbances require reseeding for successful restoration; thus, the potential exists for competition between henbane and perennial grasses commonly used in restoration projects. These competitive interactions have not, to our knowledge, been evaluated. We conducted a greenhouse study to compare the response of henbane when grown alone and in combination with three common, cool season, perennial, northern mixed prairie grass species. We examined both seedling and mature grass response to the presence or absence of henbane and the response of henbane to the grasses. Using the relative neighbor-effect index, black henbane was found to be a very poor competitor with mature grasses and two out of three seedling grasses tested. All measures of henbane growth were significantly lower among plants grown with a mature grass pot companion. Total biomass of henbane was up to 99% lower when grown with mature grasses. Mature grasses were not negatively affected when grown in combination with henbane. Western wheatgrass (Pascopyrum smithii) was the only seedling grass that was competitive with henbane but was also the only seedling grass negatively affected by henbane in both biomass and tiller production. These experiments suggest that henbane is not well suited for invasion of mature grass stands but may negatively influence some perennial grass seedlings in restoration situations.