GENUS 103. THISTLE FAMILY. 547 
103. ARCTIUM L. Sp. Pl. 816. 1753. 
Large coarse branching, rough or canescent, mostly biennial herbs, with broad alternate 
petioled leaves, and rather large heads of purple or white perfect tubular flowers, racemose, 
corymbose or paniculate at the ends of the branches. Involucre subglobose, its bracts rigid, 
lanceolate, tipped with spreading or erect hooked bristles, imbricated in many series. Recep- 
tacle flat, densely bristly. Corollas tubular with 5-cleft limbs. Filaments glabrous. Anthers 
sagittate at the base. Achenes oblong, somewhat compressed and 3-angled, ribbed, truncate. 
Pappus of numerous short serrulate scales. [Greek, bear, from the rough involucre.] 
About 6 species, natives of Europe and Asia, readily distributed, their burs adhering to animals. 
Type species: Arctium Lappa L. 
Bracts of the involucre densely cottony ; heads corymbose. 1, A. iomentosum. 
Bracts of the involucre glabrous, or slightly woolly. 
Involucre 1’ broad or more; inner bracts equalling or exceeding the flowers. 2. A. Lappa. 
Involucre 6”—9” broad; inner bracts not exceeding the flowers. , 3. A. minus, 
1. Arctium toment6sum (Lam.) Schk. 
Woolly or Cottony Burdock. Fig. 4633. 
Lappa tomentosa Lam. Encycl. 1: 377. 1783. 
Arctium tomentosum Schk. Bot. Handb. 3: 49. 1803. 
Arctium Lappa var. tomentosum A, Gray, Syn. Fl. 1: 
Part 2, 397. 1884. 
Similar to the following species; heads 8”~10” 
broad, corymbose at the ends of the branches, mostly 
long-peduncled; bracts of the involucre densely cot- 
tony, the inner ones erect and somewhat shorter 
than the flowers. 
In waste places, Massachusetts to southern New York. 
Adventive from Europe. July—Aug. 
2. Arctium Lappa L. Great Bur, Burdock or Clotbur. Fig. 4634. 
Arctium Lappa L. Sp. Pl. 816. 1753. 
Lappa major Gaertn. Fruct. & Sem. 2: 379. pl. 162. 1802. 
Stem much branched, 4°-0° high. Leaves thin, broadly 
ovate, pale and tomentose-canescent beneath, obtuse, 
entire, repand or dentate, mostly cordate, the lower 
often 18’ long; petioles solid, deeply furrowed; heads 
clustered or subcorymbose, sometimes long-peduncled, 
1-13’ broad; bracts of the involucre glabrous or nearly 
so, their spines all spreading, the inner ones equalling 
or exceeding the flowers; corolla-tube longer than the 
limb. 
In waste places, New Brunswick and Ontario to southern 
New York, and locally in the interior. Not nearly as com- 
mon as the next species in the Middle States. Naturalized 
from Europe. Other names are cockle-bur, cockle-button, 
cuckold-dock, hurr-bur, stick-button, hardock, bardane, beg- 
gar’s-buttons. July—Oct. 
