A role for inhibitors as regulators of seed dormancy in fire-dependent annuals and their nondormant (fire-independent) congeners was examined in the family Hydrophyllaceae. From seeds of the fire-dependent species, Emmenanthe penduliflora, Phacelia minor, P. brachyloba, and P. grandiflora, extracts were obtained that were found to be largely self-inhibitory and potent inhibitors of seed germination in nondormant congeners. Lower activity was detected in the fire-independent species, P. tanacetifolia and P. campanularia. The inhibitory activity was associated with the new sucrose ester, 6-O-linoleyl-alpha-D-glucopyranosyl-beta-D-fructofuranoside.