Revision of the Genus Guardiola 



By B. I.. RoiiiNSON- 



The small and natural genus Guardiola extends from the moun- 

 tains of southern Arizona to southern central Mexico. Its Mexi- 

 can distribution is a peculiar one. Well represented in the 

 northwestern states of Sonora, Chihuahua, and Tepic, it passes 

 southeastward to the state of Vera Cruz on the Gulf, but is as yet 

 unknown in northeastern Mexico and, what is more surprising, ap- 

 pears to form no part of the rich and varied vegetation of the 

 southwestern states of Oaxaca and Guerrero, the genus is well 

 marked among the mclampodioid Compositac by its peculiar habit, 

 cylindrical heads, broad thin' scarcely herbaceous much imbricated 

 involucral scales, and characteristic columnar achcnes. Mexican 

 material of the genus has of late been accumulating rapidly at the 

 Gray Herbarium and the impossibility of bringing the diverse 

 forms satisfactorily under the four or five hitherto recognized 

 species has led to the preparation of the present synopsis. 



The material of G. Tidocarpus now at hand shows that Dr. 

 Gray's varieties argiita and angustifolia arc too remote to make 

 intergradation likely, and they are accordingly here treated as in- 

 dependent species. 



Synopsis of llie SpecieH 



•^Involucral scales dorsally convex but not carinale : leaves broadly ovate to rotund, 

 cordate at the base. 

 Heads large (for the genus) and few, in terminal umbelliform cymes, these exceeded 

 in length by the .subtending foliaceous bracts : leaves sul)orbicular, closely sessile. 



I. G. ROTUNniFOLLV Robinsou, Proc. Am. Acad. 29: 317. 

 Hills near Tequila, Jalisco, Prhiglc, no. 4571. Type in herb. 



Gray. 



H- H^ Heads of medium size, often numerous, the cymes exceeding the rather small 

 subtending bracts : leaves ovate, sessile or subsessile, .-.liallowly cordate. 



2. G. PLATVPHVLLA Gray, PI. Wright. 2 : 91. 

 Arizona, by streams, .Sta. Catalina Mountains, Priuglc ; Wash 

 of El Rialta, Lcmmon ; Sonora, Wright, no. 1236 (type, in herb. 

 Gray); Thnrhcr, no. 999; Schott ; Palmer, no. 280 (coll. of 1890); 



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