That it is a plant is based on the LJLA passage associating our word with mountains. That it is reedy, on the geonic interpretation cited DJBA and at the fem. equivalent zrdh 420b. Compare bamboo, though our term is unlikely to be bamboo, which is not native to western Asia. Perhaps turmeric from Iranian; see MD p. 100a, in which case the connection with "reed" would be the shape of the root vegetable.