Ectocarpene, (+)-(6S)-(1Z-butenyl)-2,5-cycloheptadiene, is the mating pherom one of the three distantly related seaweeds Ectocarpus siliculosus, Sphacelaria rigidula and Adenocystis utricularis. Analogu es of this pheromone, differing in position and π-electron density of the double bond in the C4-side chain, were synthesized and assayed for biological activity. The results suggest, that the fundamental molecular recognition process is conservative in all species, while receptor dynamics and -topologies have been modified by individual developments and expressions during plant phylogeny.