Polyketide synthase 1 (PKS1) from Huperzia serrata is a plant-specific type III polyketide synthase that shows an unusually versatile catalytic potential, producing various aromatic tetraketides, including chalcones, benzophenones, phlorogulucinols and acridones. Recombinant H. serrata PKS1 expressed in Escherichia coli was crystallized using the hanging-drop vapour-diffusion method. The crystals belonged to space group I222 or I2(1)2(1)2(1), with unit-cell parameters a = 73.3, b = 85.0, c = 137.7 A, alpha = beta = gamma = 90.0 degrees. Diffraction data were collected to 2.0 A resolution using synchrotron radiation at BL24XU of SPring-8.