Thymelaea passerina, the spurge flax, sparrow weed, mezereon, or annual thymelaea, is a species of flowering plant in the family Thymelaeaceae. It is native to central and southern Europe, the Middle East, Central Asia, the western Himalayas, and Xinjiang in China, and it has been introduced to central North America, and to South Australia. An erect annual from tall, it is typically found in steppes, disturbed areas, and old fields.