Pollination ecology of Ranzania japonica (Berberidaceae), a perennial plant of a monotypic genus endemic to deep‐snow regions in Japan

Plants that bloom in early spring often face constraints on reproduction, which are influenced by low temperatures and unpredictable weather conditions that affect pollinator activity. We aimed to elucidate the pollination ecology and the mating system of Ranzania japonica (Berberidaceae), a perennial plant of a monotypic genus endemic to deep‐snow regions in Japan. We documented the flowering phenology and visiting insects in the field, and conducted pollination experiments by using artificial treatments. R. japonica was suggested to be self‐incompatible but not pollen‐limited. Fruit set varied between years, and florivory seemed to have a negative influence on fruit set. Insects from various taxa were observed to visit the flowers of R. japonica, with Eusphalerum sp. (rove beetle) being the most abundant, followed by Bombylius major and hymenopteran species. The stamen movement in response to insect visits was observed. The results of the observation and the pollination treatments suggested that small‐ and medium‐sized Hymenoptera were the main pollinators and rove beetles may also contribute to pollination in R. japonica. Because early spring weather can be unsuitable for activity of bees, rove beetles may act as supplementary pollinators of R. japonica. The role of the supplementary pollinators may be an overlooked but important aspect for understanding the pollination biology of early‐spring blooming plants.