174 KEY AND FLORA 



lance-shaped, with the blade extending down the stem. The entire 

 plant has a pleasant aromatic odor. Common on hills near the coast, 

 blooming in summer. 



There are several species besides these that are quite 

 common. 



Tribe 4- AMBRO'SI^E. Anthers distinct or slightly united. 

 Style abortive, truncate. Corolla of female flowers rudi- 

 mentary or none. Staminate heads generally in a cluster 

 above the pistillate ones. Receptacle with chaffy scales. 



XIV. FRANSE'RIA 



Monoecious. Staminate heads in many-flowered racemes. 

 Scales of the involucre united into a cup ; receptacle with 

 thread-like scales among the flowers. Female flowers usu- 

 ally one or few in the leaf axils, each surrounded with a spiny 

 involucre. Akenes enclosed in the persistent involucres, which 

 form burs. 



a. F. bipinnatif'ida Less. Low spreading, perennial herbs, with 

 grayish pubescent stems and leaves. Leaves twice or thrice pinnatel^ 

 divided into roundish divisions. On the coast from Washington to 

 San Diego. 



b. F. Chamisso'nis Less. Similar to the above, with which- it 

 seems to mix. The leaves are ovate or wedge-shaped, with obtuse 

 teeth. These two species grow on the sand dunes of the coast and 

 are frequently associated. 



XV. XANTHIUM, Cocklebur 



Monoecious. Male heads many-flowered, with the scales of 

 the involucre distinct in one series ; receptacle cylindrical. 

 Female heads united and enveloping the akene, armed with 

 hooked spines. These are stout annual herbs, with an abun- 

 dance of large burs in the fall. 



a. X. struma'rium L. Leaves broadly ovate, cordate, green on 

 both sides, on long petioles, rough, irregularly toothed. Burs f in. 

 long, ovate, tipped with two stout beaks. Common, introduced. 



b. X. spino'sum L. Stems much branched, very spiny, with long 

 triple yellow spines by the sides of the leaves. Leaves lanceolate, 

 white beneath, twice or thrice lobed or cut, tapering into short 



