NO. 2 



GENTRY : LAND PLANTS 



87 



Shreve, Gentry, and perhaps a few others have made some fleeting col- 

 lections on the north end. No collections are known from Sierra Seri; 

 except a few Mammillaria, there are none from Sierra Bacatete and 

 Sierra Bojihuaqueme; none from Sierra de Navachiste except Edward 

 Palmer's collections at the harbor of Topolobampo ; from Cerro Teco- 

 mate, Gentry 100 numbers; from Sierra Tacuichamona, Gentry 192 

 numbers. 



These postinsular floras should show differences from that of the 

 mainland, more or less correlated with the ages of the respective cerros 

 or with the duration of their islandic isolations. Some of them may show 

 considerable endemism, if not of species rank, then of lesser degree. The 

 rare plants that are known from only one or two restricted areas along 

 the Mexican west coast may be postinsular endemics that have persisted 

 or migrated locally since their original habitats joined the mainland. 

 Some of the cases that attract the attention at this point are the fol- 

 lowing : 



Adelia obovata Wiggins & Rollins 



Jatropha purpurea Rose 



Desmodium Wigginsii Schubert 



Lippia P aimer i Wats. 



Phrygilanthus sonorae (Wats.) Standi. 



Caesalpinia gracilis Benth. 



Karwinskia latifolia Rose 



Indigofera laevis Rydb. 



Ruellia leucantha postinsularis Gentry 



Physalis purpurea Wiggins 



Sesbania sonorae Rydb. 



Physalis sonorensis Standi. 



Prosopis reticulata Wats. 



Aloysia nahuire Gentry & Mold. 



Holographis pallida Leonard & Gentry 



Porophylluf?! pausodynum Rob. & Greenm. 



Each of these postinsular localities possesses its own floristic problems 

 in relation to the land flora. A detailed knowledge of their floras would 

 provide considerable evidence regarding their geologic histories and the 

 rate of evolution, in so far as species divergence can be chronologized 

 with physiographic developments. While it may be possible to determine 

 which plants have insular origin, it will be harder in many cases to 

 ascertain what species are of mainland origin and whose distributions 

 now represent migrations upon postinsular mountains. All such problems 



