The foxtail plant, a common annual or perennial grass weed, is a name applied to several species in the Setaria and Hordeum genera. Identifying this grass is important because of the mechanical danger it poses to pets and livestock once it matures and produces seeds. While the immature plant may appear harmless, the specialized structure of its dried seed heads can cause severe health complications for animals.
Identifying the Plant in its Vegetative Stage
Before the distinctive seed heads form, foxtail grasses look like many other common weeds, making early detection a challenge. Most foxtail varieties are summer annuals, germinating in the spring and growing rapidly through the summer months. The plant typically grows in loose, upright clumps or occasionally with a more sprawling habit.
The mature stems, which can reach heights of one to three feet, are often smooth and green, though they may display a reddish or purplish tint near the base. Leaves are generally pale green to bluish-green, with a prominent midvein running lengthwise down the center. A key feature for identification at this stage is the ligule, the small structure where the leaf blade meets the stem, which is a fringe of fine hairs rather than a continuous membrane.
The leaves themselves can vary in texture; for example, Giant Foxtail (Setaria faberi) has short, fine hairs on the upper surface of its wide leaf blades. In contrast, Green Foxtail (Setaria viridis) typically has hairless leaves.
The Defining and Dangerous Seed Head
The defining characteristic of the foxtail plant is its cylindrical, brush-like seed head, which gives the plant its common name by resembling a fox’s bushy tail. This structure is a dense cluster of seeds, or spikelets, that can range from a few inches to over half a foot in length depending on the species. As they mature in the summer and dry out, the seed heads transition from green to a straw-like tan or yellowish-brown color, becoming most hazardous.
The danger lies in the individual seeds, which are equipped with stiff, sharp projections called awns or bristles. In species like Foxtail Barley (Hordeum murinum), these awns possess microscopic, backward-pointing barbs that function like a one-way anchor. This barbed structure allows the seed to easily catch onto fur, clothing, or skin and then migrate deeper into the host with every movement, preventing the seed from backing out.
These sharp, barbed seeds can penetrate an animal’s skin, lodge between toes, or even be inhaled into the nose, ears, or lungs. They cause abscesses and severe internal damage because they do not break down inside the body. The seed heads of some species, like Giant Foxtail, tend to droop or nod, while others, such as Green and Yellow Foxtail, typically remain more erect.
Common Habitats and Geographic Distribution
Foxtail grasses are highly adaptable weeds that thrive in disturbed environments. They are commonly found along roadsides, in ditches, and throughout dry, open fields and pastures. The plant is well-suited to areas with full sunlight and is a frequent invader of neglected lawns and hiking trails, often forming dense stands.
Foxtail species are distributed throughout much of the United States, but they are particularly prevalent and problematic in the Western US, including California and other arid or semi-arid regions. These summer annuals are often the first plants to colonize bare ground. They can tolerate a range of soil conditions, including those that are dry or even slightly saline, further contributing to their widespread distribution.
Differentiation from Harmless Grasses
Distinguishing foxtail from other, less hazardous grasses is important to prevent unnecessary concern. A common look-alike is Timothy grass, which also produces a cylindrical seed head. However, a key difference is that Timothy grass is a perennial, and its seed head lacks the sharp, barbed awns found on foxtail species.
To differentiate, examine the area where the leaf meets the stem, known as the collar region. Foxtail grasses possess a ligule that is a fringe of hairs, while Timothy grass has a tall, membranous ligule. Furthermore, the stiffness of the seed head is a good indicator; the dangerous foxtail varieties have a notably bristly texture due to their many awns.