i&6 SYNGENESIA. NEGESSARIA. 



603. AMBROSIA. L, (Bitter-weed.) 

 Monoicous. — Masc. Calix 1 -leaved. Anthers 



approximate,^ but not united. Beceptacle naked. 

 — Fem. Calix 1 -leaved? entire or 5-toothed, 

 1 -flowered. Corolla none. JWt formed from the 

 indurated calix, 1 -seeded. 



Tall herbaceous and mostly annual plants; leaves roug-li, 

 the lower mostly opposite, the upper alternate, bipinna- 

 tifid, trifid, or rarely enth-e; flowers in long terminal and 

 proximately axillar spikes, upper flowers masculine nu- 

 merous, the lower fewer, feminine, glomerated, clusters 

 2 to 5-flowered, tribracteate. 



Species. 1. A. integrifolia. 2. bidentata. 3- tnjida. 4. 

 elatior. 5. artemisifolia. 6. panicxdata. 7. heterophylla. 

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

 under side white and tomentose; spikes solitary. Hab. 

 In Upper Louisiana on the banks of the Missouri; rare. 

 Only 1 or 2 feet high. 



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

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

 the Levant. 



604. XANTHIUM. £. (Clott-burr.) 

 Monoicous.- — Masc. Calix imbricated. Jln- 



thers approximate, but not united. Receptacle 

 l)aIeaceous.~FEM. Ca/io; a 2-leaved involucrum, 

 1 -flowered. Coro/Zo. none. Utricuhis muvicsLietl, 

 bifid. JVw^ 2. relied. 



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

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

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

 illar^and terminal, spike short, above masculine. 



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

 motest parts of Upper Louisiana. 2. orientale. 3. spmo- 

 sum. 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 tc 

 Europe, Siberia; India and America. 



