18 



VEGETATION OF A DESERT MOUNTAIN RANGE. 



Bajadas in seasons of well-distributed and copious rainfall. With less 

 favorable conditions they may form a very light cover or may be almost 

 absent. The total flora of root-perennials and ephemerals is large, and 

 the relative abundance of the various species fluctuates tremendously 

 from spot to spot, and in the same spot it is by no means the same from 

 year to year. This flora is nearly identical with that of the basaltic hills 

 in the vicinity of Tucson, and has been fully listed by Thornber,* with 

 a subdivision of vegetation types. 



In the following list have been brought together the names of the 

 most characteristic plants of the Upper Bajadas, grouped vegetistically 

 and briefly described. Asterisks indicate the relative abundance of 

 the species — three indicating that a plant is extremely common, two 

 that it is very common, and one that it is fairly common. Figures 

 follow the descriptions, indicating the average height of each species. 

 A comparison of all the maximum heights given will convey an impres- 

 sion of the low stature of the commonest components of the vegetation. 



Vegelistic Grouping of the Characteristic Species of the Upper Bajadas. 



Perennial Non-succulent Trees and Shrubs: 

 *** Acacia greggii, microphyllous, winter- 

 deciduous. 2 to 3 m. 

 ** Covillea tridentata, microphyllous, 

 evergreen. 1 to 2.5 m. 



* Crossosoma bigelovii, sclerophyllous, 



evergreen. 1 to 1.5 m. 



* Ephedra trifurca, aphyllous, green- 



stemmed. 0.5 to 1 m. 

 *** Fouquieria splendens, macrophyllous, 



drought-deciduous. 2 to 4 m. 



** Jatropha cardiophylla, macrophyllous, 



winter-deciduous. 0.5 to 1 m. 



* Kceherlinia spinosa, aphyllous, green- 



stemmed. 0.5 to 1 m. 

 ** Krameria glandulosa, microphyllous, 



evergreen. 1 to 2 m. 

 ** Lycium berlandieri, microphyllous, 



evergreen. 1 to 2 m. 



* Lycium fremontii, microphyllous, 



evergreen. 1 to 2 m. 

 ** Momisia pallida, sclerophyllous, ever- 

 green. 1.5 to 2.5 m. 



* Olneya tesota, microphyllous, ever- 



green (foliage occasionally winter- 

 killed). 3 to 6 m. 



*** Parkinsonia microphylla, microphyl- 

 lous, drought-deciduous, green- 

 stemmed. 2 to 5 m. 



*** Prosopis velutina, microphyllous, 

 winter-deciduous. 3 to 6 m. 

 ** Zizyphus lycioides var. canescens, 

 microphyllous, evergreen 1 to 2 m. 



Perennial Succulent Plants: 



*** Carnegiea gigantea, columnar 



branched. 5 to 14 m. 

 ** Echinocactus wislizeni, cylindrical 



0.5 to 1.5 m. 

 ** Echinocereus fendleri, cylindrical, cse 



spitose. 0.1 to 0.4 m. 

 ** Mamillaria grahami, cylindrical, soli 



tary or csespitose. 0.1 to 0.2 m. 

 ** Opuntia blakeana, flat-jointed, prO' 



cumbent. 

 *** Opuntia discata, flat-jointed, pro 



cumbent or semi-erect. 

 ** Opuntia fulgida, cylindrical-jointed 



arborescent, 1 to 2 m. 

 *** Opuntia mamillata, cyUndrical 



jointed, arborescent. 1 to 2 m. 

 ** Opuntia toumeyi, flat-jointed, pro 



cumbent. 

 *** Opuntia versicolor, cylindrical-jointed 

 arborescent. 1 to 4 m. 

 Perennial Shrublets (all less than 0.7 m. high) 



* Coldenia canescens, sclerophyllous. 

 ** Crassina pumila, dissected leaves. 



*** Encelia farinosa, macrophyllous, 



slightly drought-deciduous. 

 *** Franseria deltoidea, sclerophyllous. 

 *** Isocoma hartwegi, dissected leaves. 

 *** Kalliandra eriophylla, dissected leaves 

 ** Psilostrophe cooperi, sclerophyllous. 



* Trixis angustifolia var. laiiuscula 



sclerophyllous, shghtly drought- 

 deciduous. 



* Thornber, J. J. Vegetation Groups of the Desert Laboratory Domain. 

 Wash. Pub. 113, Chapter IV, 1909. 



Carnegie Inst. 



