no. 3 dunkle : plant ecology, channel islands 299 



Geographic Variation 



The plant life of the Channel Islands is remarkably rich and varied 

 for such a limited area. Combining Eastwood's list (1941) and Dunkle's 

 supplementary list (1942a) there are 957 species and varieties for the 

 islands. A critical examination would reveal considerable synonymity 

 and a consequent reduction of this number to about 830. In addition 

 the 150 introduced plants would reduce the number of indigenous plants 

 to about 680. The plant life is particularly remarkable on account of 

 the wide differences between the insular flora and that of the adjacent 

 mainland. This difference consists of approximately 18 per cent of en- 

 demism, considerable variation in frequency between species on the 

 islands compared with the same species on the mainland, and many 

 noticeable differences in size and growth-form. 



Several plants which are, at least locally, common and vigorous 

 on the islands but relatively rare on the mainland are : 



Fityro gramma triangularis Eriodictyon Traskiae 



var. viscosa Arctostaphylos diversifolia 



Pinus Torreyana Baeria hirsutula 



Erysimuin insulare Coreopsis gigantea 



Ribes viburnifolium 

 There are a number of species which are usually shrubby on the 

 mainland but are much more frequently arborescent on the islands, or 

 have related insular species or varities which are commonly arborescent. 

 These include: 



Quercus dumosa Ceanothus arbor eus 



Photinia arbutifolia C. crassifolius 



var. macro car pa C. megacarpus 



Cercocarpus betuloides var. insularis 



var. alnifolius Rhamnus crocea 



Prunus ilicifolia var. insularis 



Prunus Lyonii Arctostaphylos diversifolia 



There are also several genera, usually herbaceous on the mainland, 

 which have suffrutescent or woody species or varieties on the islands. 

 Among these insular forms are : 



Spergularia macrotheca S. Clokeyi 



var. Talinum Castilleja hololeuca 



Erysimum insulare C. grisea 



Lotus argophyllus C, anacapensis 



var. niveus Hemizonia clementina 



var. adsurgens Malacothrix Blairii 



Solanum Wallacei 



