s 



MISC. PUBLICATION 42 3, U. S. DEPT. OF AGRICULTURE 



gives the percentages of the total number of species in the State that 

 are represented in the several categories or in various combinations 

 of 2 categories. The species are classified on the basis of their distri- 

 bution as a whole, regardless of the fact that some of them are repre- 

 sented in Arizona only by a variety of more limited geographical range. 



Table 1. — Flowering plants and ferns of Arizona, classified according to their 

 geographical ranges outside the State, the number of species referred to each category 

 being expressed as a percentage of the total number of species known to occur in the 

 State 



Geographical category- 



Repre- 

 sentation 



Geographical category 



Repre- 

 sentation 





Percent 

 5.1 

 2.5 

 8.4 

 10.5 

 .6 

 14.6 

 1.0 

 3.1 



Tropical or subtropical 



Percent 

 6.6 



Pacific 



13 



Coloradan ___ .. . 



Rockv Mountain and Pacific 



V).0 





Great Plains 



Atlantic . ... .... . 



2.5 



Sonoran and Coloradan. _ 



.3 



Chihuahuan 



North American . 



12.0 



Chihuahuan and Coloradan-. - 



Transoceanic . . .. . 



4.8 





Adventi ve 



6.0 







The geographical categories of the flora are defined as follows: 



Endemic. — There are 163 species not known to occur elsewhere than 

 in Arizona. Of these, 45 are limited to the northern part of the State, 

 33 to the central portion, and 69 to the region south of the Gila River, 

 the remaining 16 endemic species being more widely distributed. 

 Many of the southern endemics occur so close to the Mexican border 

 that they will almost certainly be found, eventually, in Sonora or 

 Chihuahua. Some of the northern species probably occur also in 

 southern Utah, Nevada, or Colorado. 



Pacific. — Species ranging throughout all or a part of the region 

 from British Columbia to Baja (Lower) California. The number of 

 Pacific coast species extending into Arizona, excluding plants of the 

 deserts of southeastern California, is not large, but the group is of 

 interest as comprising several species found only from southern Oregon 

 to northern Baja California, and in south-central Arizona, principally 

 in the Pinal and Mazatzal Mountains. Notable examples of this 

 interrupted distribution are: Dryopteris arguta, Ribes quercetorum, 

 Cercocarpus betuloides, Lupinus succulentus, Rhus ovata, Rhamnus 

 crocea, Fremontodendron calif ornicum, Lonicera interrupta. 



Coloradan. — Occupying all or a part of the Colorado River drain- 

 age basin, from southwestern Colorado to southeastern California. 

 Most of the species of this category that reach California do not occur 

 west of the Mohave Desert and the Death Valley region. In Arizona 

 they are found mostly in the northern part of the State, commonly in 

 treeless areas or with the juniper-piny on association, at elevations 

 below 8,000 feet. The large genera Eriogonum and Astragalus are 

 well represented in this category. 



Sonoran. — Species confined mainly to the deserts at low elevations 

 in southeastern California, Baja California, northwestern Sonora, and 

 southwestern Arizona. The perennial plants of this category are 

 mostly pronounced xerophytes. This highly specialized flora reaches 

 its northeastern limit in Maricopa and Pinal Counties with such con- 

 spicuous representatives as Colubrina calif ornica, Horsfordia new- 

 berryi, Abutilon palmeri, and Beloperone calvfornica. 



