Structure and mechanical properties of fruits and seeds and their role in the dispersal mechanism of the squirting cucumber Ecballium elaterium (Cucurbitaceae)

The squirting cucumber (Ecballium elaterium) exhibits unique mechanical adaptations for seed dispersal. When ripe, the fruit explodes due to turgor pressure, ejecting seeds and fluid several meters away. Early 1900s studies examined this phenomenon, but modern techniques like 3D imaging, electron microscopy, force measurement, and high-speed video offer new insights. We investigated the plant's morphological changes during ripening using micro-CT and calculated seed ejection speed and distance with high-speed videos. The fruit stem straightens and the angle to the fruit increases to 53° upon ripening. Seeds, arranged in six longitudinal rows, reach speeds of approximately 10 m/s and distances up to 12 m. The fluid ejected with seeds likely reduces friction, and the seed envelope forms a mucilaginous coat that becomes a strong adhesive when dried, with forces up to 27.5 N. These findings enhance our understanding of this plant's seed dispersal mechanisms and adaptations for seed establishment and germination.