V. GRANT 63 



habitats than the extremes, since they are highly variable from 

 colony to colony whereas the extreme forms are quite uniform, 

 and since the variability of the intergrades shows the character 

 correlations which are expected when a hybrid segregates for 

 two or more multifactorial characters, it is judged that the inter- 

 mediates are historically more recent than the extremes and are 

 of hybrid origin between them. If Gilia capitata can be regarded 

 as a single species, therefore, it must be one of secondary origin 

 from the union of previously isolated populations. 



The most serious difficulties of classification are encountered 

 in the Gilia tenuiflora-latiflora group (Grant and Grant, 1956). 

 From the standpoint of intergradation and gene exchange the 

 whole group, comprising Gilia tenuifora, G. latijiora, G. diegen- 

 sis, G. leptantha, and G. cana, could be regarded as a single 

 species. That it is in reality more than this, however, is indicated 

 by various facts. 



The major constituents of the complex are more different from 

 one another than any conspecific elements known in the genus. 

 Each major constituent is comparable to other large species in 

 Gilia and is in fact polytypic with varying numbers of well- 

 marked subspecies. The reasoning involved in this argument does 

 not presuppose a morphological species definition but rather a 

 certain general correlation within a genus, or in this case even 

 within a section, between morphological differentiation and bio- 

 logical species formation (Mayr, 1942; Rollins, 1952). 



The treatment of Gilia teniiifloia, G. latiflora, and G. cana as a 

 single species would obscure rather than accurately portray their 

 relationships. Each species named has other genetically close rel- 

 atives which are without question specifically distinct, whereas 

 a pronounced reduction in fertility associated with a lowered 

 degree of chromosome pairing is found in the hybrids between 

 the major elements. Finally, a number of sympatric occurrences 

 are known between the major elements. All these facts are diffi- 

 cult to reconcile with the idea that the major entities in the Gilia 

 tenuiflora complex are the members of a single species in any 

 normal sense of the word. 



The existing evolutionary pattern in the Gilia tenuijlora group 



