Physical properties of Triadica sebifera seeds collected from introduced (USA, black) and native (China, white) ranges. (a) Volume, (b) mass, (c) coat thickness, (d) coat hardness. Seed coat hardness was measured using seed break force. Seed sources, collection times and number of replicates are given in Supplementary Tables S1 and S2. Means + 1 SE are shown. Differences between origins were determined by nested ANOVAs with origin as fixed effect and populations as random effect nested within each origin.