Mangrove seedlings establish in highly dynamic intertidal environments characterized by tidal inundation, salinity and unstable substrate, where early anchorage and upright orientation are critical for survival and light perception for growth. In crypto-viviparous mangrove Avicennia marina, the functional role of the hypocotyl during post-dispersal establishment remains poorly understood. This study examines the importance of the hypocotyl and the largest diameter adventitious root R1 in contributing to seedling uprightness.