Purple starthistle (Centaurea calcitrapa):
        Purple starthistle is a biennial that sometimes acts as an annual or a short-lived perennial. Mature plants are 1 to 4 feet tall, have a stout taproot, and are densely and rigidly branched. Purple starthistle is native to Asia Minor from a region between the Black and Caspian seas. It was first detected in California near Vacaville in 1886 (1). Similar in some respects to yellow starthistle, this is an aggressive Centaurea, that is a problem on annual rangelands in the San Francisco Bay area. it tends to occur on sites more mesic (moist) than those occupied by yellow starthistle. When the two species occur together, purple starthistle grows on heavier bottomland soils. Grazing animals generally avoid purple starthistle, but may eat the young rosettes if other feed is not available.
        Nutrients: We sampled purple starthistle with and without spines and its roots and found that in all cases, it is comparable to alfalfa in nutritional value. As the root was being dried it gave off an aroma similar to a sweet baked potato. A 2002 study showed that ethnic Albanians living in Italy gather and eat the plant's young whorls. Researchers have also found that extracts from the plant do a better job of degrading milk caseins and suggest that these extracts should be used as an alternative to commercial animal rennets in the manufacture of cheese.
        Toxins: There are no known cases of poisoning of animals eating purple starthistle. We are gathering additional information.