Hydration history and attachment morphology regulate seed release in Chorizanthe rigida (Polygonaceae), a serotinous desert annual.

• Premise of the study: Most seed dispersal studies focus on the spatial aspects of propagule dissemination, i.e., the movement of seeds away from the mother plant. However, the timing of seed release can also be a critical variable influencing the probability of seedling survival. We used a biomechanical approach to analyze seed release in Chorizanthe rigida, a serotinous desert annual, to understand the adaptive significance of seed retention in this species.• Methods: We performed pull-to-break tests on individual propagules (i.e., involucres and achene) from newly developed and older plants, under dry and wet conditions, and recorded the breaking force. We measured the involucral base area using digital images and image processing software.• Key results: There is a positive correlation between the force required to detach an involucre and the size of its base area. The force required to detach involucres from soaked and older plants was lower than that for dry and new plants. This pattern provides a mechanism for the plant to regulate the number of involucres released in different rain events.• Conclusions: Seed release in C. rigida is mediated by propagule morphology, rainfall conditions, and age of the dry plant. These factors allow this species to cope with desert environmental variability by influencing the timing and number of seeds released.