Comparative reproduction biology of three co-occurring Impatiens species.

Two alien Impatiens species are spreading in Europe and share habitats with the native Impatiens noli-tangere. We studied their reproductive biology to estimate which traits facilitate invasiveness. Flower morphology was examined, insect observations were made, and hand pollination treatments were performed. Floral biology differed among species. Impatiens glandulifera and I. noli-tangere presented large quantities of sucrose-dominant nectar, contrary to Impatiens parviflora. The latter had high autonomous selfing ability (81.4% fruit set) linked to complete self-compatibility. No inbreeding depression was detected for this species. The second alien, I. glandulifera, showed lower autonomous selfing (9.3% fruit set), with high self-compatibility and low inbreeding depression (). No evidence of autonomous selfing was found for the native, which presented the lowest self-compatibility and the highest inbreeding depression (). However, all species can be considered self-compatible. Impatiens glandulifera flowers were visited by insects up to 250 times during their life span, whereas I. noli-tangere and I. parviflora flowers received fewer than seven visits. Both exotics present traits facilitating reproductive success. Impatiens parviflora exhibits autonomous self-pollination, whereas the other species possess attractive traits with respect to insect pollination. On the other hand, the native, unable to self-pollinate, is poorly attractive to pollinators. The high fecundity of the aliens seems to contribute to their invasiveness.