Delayed selfing in an alpine biennial Gentianopsis paludosa (Gentianaceae) in the Qinghai-Tibetan plateau.

Delayed selfing could provide ovules with an opportunity to be fertilized as a means of "pollination assurance" before the flowers wilt. It could, thus, be regarded as an adaptation to unpredictable pollinator environments. Within the alpine biennial Gentianopsis paludosa, the showy flowers and herkogamy at the early stage of a flower's life cycle may favor outcrossing. As the flower ages, anthers contact the central stigma due to the elongation of all filaments, resulting in autonomous selfing. Flower visitors are extremely rare in a high altitude population; and examination of the mating system indicates that G. paludosa is self-pollinated under natural conditions in this population. While at the lower altitude, the bumblebee visitation rate is relatively high but possibly unreliable. Stigma receptivity is the highest on the third day of anthesis, and decreases thereafter. Pollen viability is the highest when flowers open, and gradually decreases later. Self-pollination of G. paludosa occurs at the late stage of a flower's lifecycle when stigma receptivity and pollen viability have both decreased, suggesting delayed selfing and assurance of seed production. This delayed selfing could assure seed production under the constraints of pollinator scarcity, but ensure outcrossing when pollinators were available. Such a flexible pollination mechanism is highly adaptive in the alpine environment of the Qinghai-Tibetan Plateau.