Flower structure and floral reward in Scopolia carniolica (Solanaceae) – is it a plant that can support the bumblebee food base in early spring?

Scopolia carniolica Jacq. is a perennial plant from the family Solanaceae. The study objective was to examine floral traits that may be important for interactions with floral visitors (i.e., blooming phenology, floral micromorphology, nectary characteristics, nectar quantity, nectar sugar composition, and pollen production). In S. carniolica, papillae, numerous non-glandular trichomes, and a few glandular trichomes were present on the inner corolla epidermal surface. Lipids, acidic lipids, tannins, and alkaloids were present in the non-glandular trichomes and in the corolla cells. The discoid-type nectary was located at the base of the ovary. Floral nectar was released through nectarostomata. The process of nectar release started in the bud stage (ca. 5–8 h before corolla opening) and continued to the 4th day of anthesis. The amount of secreted nectar peaked in 2-day-old flowers. The amount of produced nectar, nectar sugar concentration, and sugar mass varied significantly across years. On average, the total mass of sugars in the nectar was 0.54 mg/flower. S. carniolica produced sucrose-dominant nectar with no glucose. The sugar proportions did not differ during the flowering season. On average, 1.95 mg of pollen per flower was produced. Among floral visitors, bumblebees were most frequently noted, accounting for 79.7% of the total number of floral visitors to S. carniolica flowers. The species can be used in early spring ornamental arrangements to support the food supply for insects, mainly bumblebees.