308 allan hancock pacific expeditions vol. 13 



Affinities of Island Plants 



The origin of the present plant life of the islands is inevitably 

 bound up with the geological vicissitudes of the past. During the warm, 

 moist conditions of the early Miocene, when the ancient land of Catalinia 

 was presumed to have been connected with the mainland (Reed, 1933), 

 a large element of the flora then existing must have reached the insular 

 area. Following the hypothetical almost complete submergence of Cata- 

 linia during the upper Miocene and its re-emergence during the Pliocene, 

 the region may have been invaded by a Mexican flora which was adapted 

 to the relatively warm and dry climate of that time. While there is no 

 direct evidence of land connections with the mainland during the Plio- 

 cene a large element of Baja California flora on the islands seems to 

 render probable some temporary connection, which may have been 

 established during these millions of years. ^ The Mexican element of 

 the insular flora contains such genera as Crossoso?na, Cereus, Galvesia, 

 and Lycium. Many of the endemics listed in table 7 are probably of 

 Mexican derivation. Thirty-two other plants of probable Mexican 

 aflfinity which are to be found also to the south are included in table 8 

 under the heading ''southern." 



Northern Elements 



Another large element of the insular flora is shown in table 8 by 

 the sixty-five "northern" plants which are otherwise mostly found 

 north of the Cuyama River. Munz (1935) lists thirty-five plants of 

 the nothern group of islands which otherwise occur mostly from 

 Monterey County northward on the mainland. Leconte (1888) has 

 stated that during the glacial periods of the Pleistocene there must 

 have been a southward migration of northern flora, which reached the 

 islands during periods of uplift sufficient to have created mainland 

 connections. At the same time the warmer climate of the islands and 

 the protected coves along the coast must have harbored many of the 

 Mexican and Great Basin plants which are presumed to have reached 

 the islands from mainland California during the milder climates of 

 the Miocene and Pliocene. Thus this glacial invasion may have included 

 many relicts of previous northward Mexican migrations as well as 

 the many plants of northern affinity which have so enriched the flora 

 of the islands, especially those of the northern group. 



SThis was also held tenable by Le Conte (1888) who stated that the islands 

 were probably connected with the mainland during the late Pliocene and early 

 Quaternary. 



