Floral biology and breeding system of Impatiens balfourii (Balsaminaceae): An exotic species in extension in temperate areas

• Impatiens balfourii offers high quantities of sucrose dominant nectar.
• Impatiens balfourii is self-compatible and does not suffer from inbreeding depression.
• High fecundity and high attractiveness might contribute to its high reproductive output.

Annual alien species are dependent on their sexual reproductive success to establish, maintain and spread their populations. As the annual exotic Impatiens balfourii (Balsaminaceae) is spreading in several temperate countries, we assessed its characteristics linked to sexual reproduction. The reproductive traits and the breeding system which could indicate some trends that might favour population spread and invasion were examined. Hand pollination treatments were performed under controlled conditions to evaluate (1) autonomous selfing ability, (2) self-compatibility and (3) inbreeding depression. Floral biology including morphology as well as nectar and pollen production was also assessed.Impatiens balfourii presented large quantities (6.7 μl/flower) of sucrose dominant nectar. Sucrose dominant nectars are known as highly attractive for bees, potential pollinators of I. balfourii. Total sugar concentration of the nectar (47%) was high and situated within the range of bee-pollinated plants. Following hand pollination treatments, fruit and seed sets were similar after cross- and self- pollination. The species was thus self-compatible and no inbreeding depression was detected. The flowers were not totally protandrous as the stigmas were already receptive at bud stage. Autonomous selfing ability was high at the seed but low at the fruit level. In conclusion, the species presents traits linked to a high attractiveness for pollinators and a high fecundity that might allow high reproductive output. The invasive potential still needs to be estimated.