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Field invaded by medusa head: Credit: Stephen Novak
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Patch of medusa head: Credit: Rene Sforza
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Single medusa head plant: Credit: Rene Sforza

Medusahead (Taeniatherum caput-medusae) is an invasive common throughout the Pacific Northwest. It is a problem in rangelands where it outcompetes native species important to livestock. This plant is known for its characteristic seedhead that resembles the head of the mythical figure Medusa, where it gets its name. 


Identification guide: Taeniatherum caput-medusae


Medusahead is extremely easy to identify because of its distinctive seedhead, which resembles that of the mythical figure Medusa who had snakes for hair (hence its name). The seedhead, called a “spike”, is ball shaped with long twisted awns that emerge from it. The spike contains glumes which are short and at a 45 degree angle (labelled here as “short awns”) and long awns directed (pointed) upward (Fig 1). The plant germinates in the fall, and spends the winter as a seedling. As it grows in the spring it has a dark green color and after it has produced seeds it dries to a light yellow (straw) color.  Mature plants can reach a height of 6-24 inches (Fig 2). In the western United States (US) two plant species that can be mistaken for medusahead: bottlebrush squirrel tail (Elymus elymoides) and foxtail barley (Hordeum jubatum) (Fig 3). While the spike of medusahead remains intact as it matures (difficult to shake apart), the spikes of these other two species tends to fall apart more easily (especially as bottlebrush squirrel tail matures). 

Fig 1. How to identify medusahead. Photo credit: Dorothy Maguire


Background: Medusahead (Taeniatherum caput-medusae) also known as  medusahead rye or rough medusahead is native to southern Europe (Portugal and Spain in the west, and eastward to Ukraine and Russia), north Africa (Morocco, Algeria) and central Asia. It was first collected near Roseburg, Oregon in 1884; and it was probably brought to the US accidentally as a contaminant in agricultural products. Currently its distribution in the western US spans California, Idaho, Nevada, Oregon, Utah and Washington, and it was recently reported for the first time (2013) in Montana. In general, this species prefers regions characterized by clay soils, which have dry summers, and moist cool winters. It often invades areas that are already disturbed such as roadsides and areas which have been overgrazed. 

Fig 2. The development of medusa head over the course of a growing season. Photo credit: Dorothy Maguire


Prevention of spread: In order to prevent spread of this species, it is advised to avoid traveling through areas that have dense populations because the seeds are easily transferred to clothing and animal fur. Care should be taken to limit disturbances (e.g. over grazing) that facilitate invasion. Planting native perennial grasses has been shown to prevent reestablishment of medusahead by 15-20 percent. Generally, once an invasion has established, an integrated approach seems to be the best course of action with combinations of burning, tillage and herbicide application. Currently, researchers are searching for biological control agents in medusa head’s native range, results of these studies however are still pending.

Fig 3. How to tell medusahead apart from its look alike. Photo credit: Dorothy Maguire.


Impact: Medusahead now dominates over 2.5 million acres of land across the USA. The species has particularly harmful in rangelands because of its high silica content which makes it unpalatable to livestock and wildlife).  Dense medusahead stands can reduce grazing productivity by 80 percent. In addition, due to its high silica content, medusahead tissues degrade slowly and layers of plant biomass build up over several years.  This build-up of biomass can smoother native plant species.  Thus, medusahead infested sites have lower native plant biodiversity, and altered community structure. 

Because medusahead is a winter annual, it resumes growth early in the spring and acquires resources (soil moisture and nutrients) before native perennial plant species. The build-up of medusahead biomass, in combination with other invasive plant species such as cheatgrass, creates fuel that has altered the fire regime of sagebrush steppe ecosystems.  Range fires now occur more frequently and more intensely.  This altered fire regime has major negative impacts on people by increasing the risk of fires occurring, and by fundamentally altering ecosystem dynamics. Finally, the shallow root system of this grass makes the soils it invades prone to erosion, and less resistant to any form of disturbance. Medusahead severely reduces the conservation value of areas it invades.