Ethylene is a gaseous phytohormone involved in various physiological processes including fruit ripening, senescence, root hair development, and stress responses. Recent genomics have suggested that most homologous genes of ethylene biosynthesis and signaling are conserved from algae to angiosperms, whereas function and biosynthesis of ethylene remain unknown in basal plants. Here, we examined physiological effects of ethylene, an ethylene precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), and an inhibitor of ethylene perception, silver thiosulfate (STS), in a basal land plant Marchantia polymorpha. M. polymorpha plants biosynthesized ethylene and treatment with high concentrations of ACC slightly promoted ethylene production. ACC remarkably suppressed growth of thalli (vegetative organs) and rhizoids (root-hair-like cells), whereas exogenous ethylene slightly promoted thallus growth. STS suppressed thallus growth and induced ectopic rhizoid formation on the dorsal surface of thalli. Thus, ACC and ethylene have different effects on vegetative growth of M. polymorpha. We generated single and double mutants of ACC synthase-like (ACSL) genes, MpACSL1 and MpACSL2. They did not show obvious defects in thallus growth, ACC content, and ethylene production, indicating that MpACSL genes are not essential for the vegetative growth and the biosynthesis of ACC and ethylene. The gene expression analysis suggested involvement of MpACSL1 and MpACSL2 in stress responses. Collectively, our results imply ethylene-independent function of ACC and the absence of ACC-mediated ethylene biosynthesis in M. polymorpha.