260 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 13 



in the arid maritime; while the southern one-third of San Clemente 

 would be provisionally in the desert maritime. Of the three factors 

 which m.ight account for this desert aspect of the vegetation at the 

 southern end of San Clemente Island: climate, soil, and topography; 

 the climate is apparently the limiting factor. The soil of the entire 

 island is of volcanic origin, while the southern exposures of the other 

 islands have no similar vegetation. 



Certain plants may well be used as indicators for the sub-divisions 

 of the maritime climate. Thus the following species are suggested for 

 the semi-humid region: 



Pinus jnuricata Malvastrum Nutiallii 



Abronia umhellata Oenothera cheiranthifolia 



Myrica calif ornica Mimulus longiflorus 



Lupinus Chamissonis Erigeron glaucus^ 



Illustrative of plants found in the area designated as arid maritime 

 are: 



Abronia umbellata platyphylla Lyciuju calif ornicum 



Opuntia prolifera Mimulus puniceus 



Oenothera bistorta Coreopsis ?naritima 



The vegetation of the southern one-third of San Clemente has a 

 true desert aspect and resembles that of the Baja California coast south 

 of Cabo San Quintin. The following plants appear to be limited to this 

 area, or appear only sporadically on southern exposures of the arid 

 maritime : 



Euphorbia misera Senecio Lyonii 



Notholaena Newberryi Phacelia floribunda 



Cereus Emoryi Lupinus argophyllus adsurgens 



Cereus Emoryi and Opuntia prolifera are dominant here, showing 

 an abundance and luxuriance which can only be equalled south of Cabo 

 San Quintin. Furthermore, the aspect of the vegetation of the northern 

 two-thirds of San Clemente Island is distinctly different from the 

 succulent-suffrutescent shrub type of the southern one-third. The north- 

 ern uplands bear a typical grassland association with very little cactus. 

 Thus the marked differences in vegetation and the accompanying 

 variation In the precipitation, appear to justify the division of the mari- 

 time climate Into the three sub-types. 



2The nomenclature followed in this paper is that of Munz (1935) in his 

 Manual of Southern California, with certain changes by Dunkle (1940, a, b, c, 

 1941, and 1942, a, b.) Author's citations for each species are provided in the 

 tables of sections IV, V, and in section VIII. 



