Taeniatherum caput-medusae (Medusahead, Medusahead wildrye; syn. Elymus caput-medusae L., Taeniatherum asperum Nevski) is an invasive species in the Poaceae family. This plant is cited as a noxious weed in several countries; for example Brazil and the United States. It is native to the Iberian Peninsula and northeast Africa.
Medusahead is a thin, straight, upright grass when it is green. As it dries and browns, the awns expand and fan out, sending a mass of bristles in all directions. The wild arrangement brings the grass its common name, after Medusa of Greek myth with her head of snakes. Medusahead is otherwise similar in appearance to foxtails. Medusahead can be easily identified in a field, as it matures a few weeks after most other grasses, and so can be seen as green patches in fields of brown or gold.
The grass spreads by seeds, each of which has a very long awn. They easily tangle in the coats of livestock and bales of hay. The plant is rich in silica when mature, and so makes unpalatable fodder.