186 SYNGENESIi. NECESSARIA, 



603. AMBROSIA. X. (Bitter-weed.) 

 Monoicous. — Masc. Calix 1 -leaved. Anthers 



approximate, but not united. Receptacle naked. 

 — Fem. Calix 1-leavedj entire or 5-toothed, 

 ] -flowered. Corolla none. J\%t formed from the 

 indurated calix, 1 -seeded. 



Tall herbaceous and mostly annual plants; leaves rough, 

 the lov.er mostly opposite, the upper alternate, bipinna- 

 tifid, ti-ifid, or rarely entire; flowers in long terminal and 

 proximately axillar spikes, upper flowers masculine nu- 

 merous, the lower fewer, feminine, glom crated, clusters 

 2 to 5-flowered, tribracteate. 



Species. \. K.integrifoUa. 2. bi dent at a. 3- trifida. 4. 

 elatior, 5. artemisifoUa. 6, paniculata. 7. heterophylla. 

 8. • tomentosa. Perennial; stem low; leaves bipinnatifid, 

 under side white and tomentose; spikes solitary. Hab. 

 In Upj)er Louisiana on the banks of the Missouri; rare. 

 Only 1 or 2 feet high. 



A North American genus, wuth the exception of 1 spe- 

 cies in Peru and another indigenous to the sea-coasts of 

 the Levant. 



604. XANTHIUM. L. (Clott-burr.) 

 Monoicous Masc. Calix imbricated. An- 

 thers approximate, but not united. Receptacle 

 X)aleaceous.— Fem. Calix a 2-leaved involucrum, 

 1 -flowered. Coro//a none. I7fna*/?is muricatcd, 

 bifid. JSut 2.celled. 



Herbaceous and annual; leaves entire or 3-lobed, alter- 

 nate, smooth or asperate; (in X. spinosum the leaves are. 

 subtended by large and trifid spmes); flowers spiked, ax- 

 illarjand terminal, spike short, above masculine. 



Species. 1. X. Strumarinm. Indigenous to the re- 

 motest parts of Upper Louisiana. 2. orientale. 3. spino-^ 

 ^ufn. At this time naturalized from Savannah in Georgia 

 to Georgetown in the District of Columbia, v. v. 



A genus of 4 species indigenous nearly in common to 

 Kurope, Siberia, India and America. 



