Harsh climates should select for breeding systems that uncouple reproductive success from unpredictable pollinator service, such as autonomous, within-flower pollination and autogamous seed set. I assessed the breeding system and overall pollinator dependence of Tristerix corymbosus (L.) Kuijt, a mistletoe that blooms during the snowy winters of the southern Andes and whose flowers are visited by the hummingbird Sephanoides sephaniodes. The nectar produced by T. corymbosus represents the main food for overwintering populations of S. sephanioides, one of the principal pollinators in the temperate forest of southern South America. Hand-pollination experiments showed that this plant is fully self-compatible, with only a slight advantage of cross- over self-pollen during either germination or early tube growth. Despite self-compatibility, T. corymbosus exhibited a limited capacity for autonomous, within-flower pollination and high dependence on its hummingbird pollinator for full seed set. Thus, dwindling hummingbird populations should compromise reproductive success in this potential keystone plant species.
