Flowering, pollen production and insect visitation in two Aconitum species (Ranunculaceae)

Abstract

Flowering phenology, diurnal dynamics of blooming, insect visitation and pollen production in <em>Aconitum lycoctonum </em>L. and <em>Aconitum carmichaelii </em>Debeaux were investigated in 2012–2013 in the Lublin area, SE Poland. Flowering of <em>A. lycoctonum </em>occurred in June/July, whereas <em>A. carmichaelii </em>bloomed in September/October. Both <em>Aconitum </em>species differed in terms of the diurnal pattern of flowering. The flowers of <em>A. lycoctonum </em>started opening at 5.00, whereas those of <em>A. carmichaelii </em>started blooming at 8.00 (GMT+2h). The species differed in the number of anthers per flower, the size of anthers, and the mass of pollen produced in anthers. As a result, the flowers of <em>A. lycoctonum </em>produced less pollen (mean = 1.0 mg per 10 flowers) than the flowers of <em>A. carmichaelii </em>(mean = 8.2 mg per 10 flowers). The estimated pollen yield was 0.2 g per m² for <em>A. lycoctonum </em>and 1.6 g per m² for <em>A. carmichaelii</em>. The flowers of both <em>Aconitum </em>species were foraged exclusively by bumblebees with the predominance of the long-tongued <em>Bombus hortorum</em>. Nectar was a more attractive floral reward than pollen. The propagation of <em>Aconitum lycoctonum </em>and <em>A. carmichaelii</em> in ornamental gardens may support the conservation of bumblebees whose populations are steadily declining.