802 



MANUAL OF POISONOUS PLANTS 



yellow; receptacle flat and bristly; corolla-tube slender and S-cleft or S-lobed; 

 anthers sagittate at the base; achenes oblong or obovoid; pappus of several 

 series of bristles and scales. 



About 350 species mostly of the old world where they are troublesome 

 weeds. The common bluebottle or corn flower is frequently cultivated in 

 gardens and is a frequent escape from cultivation. 



Fig. 458. Flowers of centaurea. 1, Flower; a, anther; 2, style. At the left, Achene 

 and Pappus. 



Centaurea solstitialis Linn. Knapweed 



Erect, branched, cottony, stems winged, lower leaves lyrate, upper linear 

 entire, decurrent, spines of upper bracts long spreading with a few smaller ones 

 at the base, pappus soft. 



Distribution. Fields in California, also in Europe and England, rare; in- 

 troduced with alfalfa. Introduced into Iowa with alfalfa seed. 



Injurious properties. Because of the spiny character of the plant it is often 

 troublesome to man and animals. 



29. Silybum (Vaill.) Adans. Milk Thistle 



Annual or biennial, much branched herbs ; leaves large, alternate, clasping, 

 white-blotched ; heads discoid, solitary at the end of the branches ; involucre 

 large ; bracts rigid, some armed with large spreading or recurved spines ; flowers 

 all tubular ; corolla-tube slender, top 5-cleft ; anthers sagittate ; achenes obovate- 

 oblong; pappus-bristles in several rows. 



A single species, native to the Mediterranean region. 



Silybum Marianum (L.) Gaertn. Lady's Thistle 



A tall branched glabrous annual with striate stem ; leaves oblong lanceolate, 

 prickly clasping. 



Distribution. Occasionally found eastward especially in ballast and common 

 on the Pacific coast, from British Columbia to Southern California. 



Injurious properties. The spiny leaves and involucre have been trouble- 

 some; produces mechanical injuries. 



