Biflavonoids have been isolated from a wide variety of plant species, but little is known about their native biological functions. Here we report a possible ecological role for biflavonoids by describing the isolation of the biflavonoid 4',4‴,7,7″-tetra-O-methylcupressuflavone (1) from Araucaria columnaris and its inhibitory effect on seed germination. Compound 1 was isolated from needles of a single A. columnaris specimen and inhibited germination of Lactuca sativa seeds in a culture-dish assay; it was also detected in soil samples under the canopy where reduced germination was observed, but not in a location away from the canopy where germination was uninhibited.