Ecology and Management of Tarweed Ecology and Management of Tarweed Yellow tarweed, Holocarpha virgata , is a native plant that is well adapted to the hot dry summers in the Central Valley of California and the surrounding foothills.
Tarweed is in the Composite family.
It was first classified as Hemizonia virgata . In the summer tarweed's aromatic summer growth is sometimes tall and sticky. It is not palatable to livestock, hides forage needed by livestock, and coats the faces and legs of livestock with a tarry resin. With the arrival of Europeans, California's grasslands changed dramatically. Annual grasses and forbs from the Mediterranean area were introduced both accidentally and intentionally.