242 standley: floras of new Mexico and Argentina 



(Anacardiaceae) , Cristaria (Malvaceae), Hippeastrum (Amaryl- 

 lidaceae) , Margyricarpus (Rosaceae) , Boagainvillea (Allioniaceae) , 

 Arjona (Santalaceae) , and Hypochaeris (Cichoriaceae) . Most 

 of these have no obvious analogues in the United States, al- 

 though Oxystelma and Turrigera may correspond to our Phili- 

 bertella, and Adesmia in a manner take the place of Astragalus 

 or perhaps Lotus. The family Mutisiaceae reaches its greatest 

 development in the arid regions of western and southern South 

 America. In North America it is represented in Mexico and the 

 southwestern United States chiefly by the genera Trixis and 

 Perezia. 



Many of our characteristic New Mexican genera, on the other 

 hand, are not found in Argentina. Among them may be men- 

 tioned Tridens, Sitanion, Yucca, Eriogonum, Abronia, Dithyraea, 

 Koeberlinia, Fouquieria, Oreocarya, Hymenopappus, Toivnsendia, 

 and Chrysothamnus. 



From all the analogies of the two floras that have been cited it 

 is evident that the relationship between the vegetation of southern 

 Argentina and that of New Mexico is strongly marked. The 

 limited size of Mr. Fischer's collection affords, of course, an in- 

 sufficient basis for an extensive comparison of the vegetation of 

 these areas, but the data afforded by other collections only accen- 

 tuate the closeness of the relationship. It is evident that stu- 

 dents of the flora of the southwestern United States would do 

 well to devote more- attention to the flora of the corresponding 

 regions of South America. No doubt many of our United States 

 species find their closest allies in those regions, and it may well be 

 that in some cases identical forms common to the two areas have 

 been described independently by botanists who relied too much 

 upon geographic isolation in establishing their species. Prob- 

 ably, however, such instances are few. The botanists of Cali- 

 fornia long have been aware of the relationship of their xerophytic 

 flora to that of Chile, and have profited by this knowledge. Un- 

 fortunately the plants of southern and western South America 

 are too poorly represented in United States herbaria at present 

 to furnish an adequate basis for comparative studies* of the flora. 



