BLUE AND PURPLE GROUP 



Canada Thistle 



C. arvense. — Color, rose purple. A perennial from a creeping 

 rootstock which spreads the faster from being cut. Leaves, lance- 

 shape or oblong, much cut, prickly along the margins, sessile, 

 but not running down on the stem. 



In fields and cultivated ground, so troublesome a weed it 

 can only be eradicated by frequent, deep plowing. 



Pasture or Bull Thistle 



C. pumUum. — Color, purple. Heads of flowers, very large, 2 to 

 3 inches broad, with leafy bracts below them. Leaves, green 

 both sides, cut into acute, prickly, pointed lobes, the upper sessile, 

 clasping; the lower, petioled. Stem, stout, low, leafy, 1 to 3 

 feet high, from solid, thick, and much-branching roots. Flowers, 

 fragrant, sometimes white. July to September. 



Dry soil, fields and pastures. New England to Delaware 

 and Pennsylvania. 



Tall or Roadside Thistle 



C. altissimum. — Color, light purple. Leaves, whitish under- 

 neath, rough-hairy above, oblong or lance-shape, bristly toothed, 

 margined, not so deeply cut as some of the species. Heads of 

 flowers, 2 inches across, single at the ends of branches. Involucre- 

 bracts tipped with a dark glandular spot. Very tall, reaching a 

 limit of 10 feet. August and September. 



Rough, leafy, much-branched biennials or perennials, in 

 fields and woods from Massachusetts to Minnesota and 

 southward. 



Since thistles are protected from grazing cattle by their 

 spiny nature, and since by their plumed seeds they are easily 

 and widely disseminated, they are among the most formi- 

 dable of weeds, almost impossible to eradicate when well 

 established. Many old fields are a mass of thistles. 



Swamp Thistle 



C, muticam. — Color, dark purple. Leaves, very deeply cut and 

 the divisions very prickly. Flower-heads, large, on leafless pe- 

 duncles, with a few bracts near the base, terminal. Stem, tall, 

 3 to 8 feet high, angled, woolly when young, smoother with age. 

 Involucre, not prickly. July to October. 



Common in swamps and wet woods, New England to 

 Florida and westward. 



24 367 



