COMPOSITAE THISTLE FAMILY RAGWEED 765 



filiform chaff ; corolla f unnelf orm, 5-toothed, anthers but slightly united ; achenes 

 ovoid. 



The twelve species are mostly native of North America. 



Ambrosia trifida L. Great Ragweed, Ironweed 



A stout, scabrous, hispid or nearly glabrous annual, 3-12 feet high; leaves 

 opposite and petioled, 3-nerved, deeply 3-5-lobed, the lobes ovate, lanceolate 

 and serrate, the upper leaf sometimes ovate and undivided; flowers monoecious, 



Fig. 442. Ambrosia showing flowering stalk, pistils, stamens, and longi- 

 tudinal sections of stamens in perianth and ovary. (After Faguet). 



