412 Ambrosiae 



corolla none ; pappus none. Involucre of the staminate 

 heads hemispheric, 5-12-lobed, open, many-flowered ; 

 corolla funnelform, 5-toothed ; anthers scarcely coherent, 

 mucronate-tipped. 



1. A. psilostachya DC. Stems erect from horizontal root- 

 stocks, 5-8 dm. high, with strigose pubescence and somewhat 

 scabrous ; leaves once or twice pinnatifid ; fruit mostly solitary 

 in the axils, turgid-ovoid, about 3 mm. long, obtusely short- 

 pointed, rugose-reticulate, either unarmed or with 4 short or sharp 

 tubercles. 



A common weed in low ground, especially in our coast valleys. June- 

 September. 



27. GAEBTNEBIA Med. 



Hispid or tomentose branching herbs, sometimes woody 

 at the base, with mostly alternate lobed or divided 

 leaves, and small monoecious greenish heads of discoid 

 flowers, the staminate in terminal spikes or racemes, the 

 pistillate solitary or clustered in the upper axils. Invo- 

 lucre of the pistillate heads ovoid or globose, closed, 1-4- 

 celled, 1-4-beaked, armed with several rows of spines 

 and forming a bur in fruit ; corolla none ; style-branches 

 exserted ; achenes obovoid, thick, solitary in the cells ; 

 pappus none. Staminate heads sessile or short-ped- 

 uncled, their involucres broadly hemispheric, open 5-12- 

 lobed ; receptacle chaffy ; corolla regular, with short 

 tube and 5-lobed limb ; anthers scarcely coherent, 

 mucronate-tipped. 



1. G. tenuifolia (Gray) Kuntze. Perennial, erect, 4-15 dm. 

 high, leafy throughout, hispid or varying to glabrate; leaves 

 mostly 2-3-pinnately parted or dissected into narrow oblong or 

 linear lobes, the narrow rachis often with a few interposed small 

 lobes, the terminal elongated; staminate racemes elongated and 

 paniculate; pistillate heads in numerous glomerules below, in 

 fruit minutely glandular, about 2 mm. long, armed with 6-18 

 short and stout incurving spines, their tips usually hooked and 



